For the 3.8 code version, the datalogged variables are:

Datalog Label	INI Variable	Code Variable (outpc.)	Description
Time	time	none	This is a time variable generated by TunerStudioMS that counts up with the tuning PC's clock. It is helpful for spotting gaps in the datalog (which can be caused by changing dialog pages (datalogs are not recorded if the user is on some pages) or communications issues.)
SecL	seconds	seconds	This is the internal CPU clock from the controller's processor.
RPM	rpm		This is the engine rpm (revolutions per minute).
MAP	map	map	The engine intake manifold kPa from the Manifold Absolute Pressure (MAP) sensor.
Tbl Indx	kpaix	kpaix	The current MAP value (above) divided by the current baro value to be used as an alternative load index. Baro pressure is not in the default datalog (the baro correction amount, Gbaro is, but not the baro value the correction is based on). Baro can be added by including the line: entry = baro, "baro", float, "%.1f" in the [Datalog] section of the INI.
MAF	maf	maf	This is the Mass Air Flow value determined from the MAF sensor feedback and the MAF table.
TP	throttle	tps	Throttle opening position in %, 0% is closed, 100% is WOT, if the TPS has been calibrated properly.
vBatt	batteryVoltage	batt	This is the battery voltage as measured at MegaSquirt-II.
if NARROW_BAND_EGO O2 elif LAMBDA Lambda else AFR	egoVoltage lambda1 afr1	ego1, ego2	This is the ego sensor output voltage (if a narrow band sensor is selected).
IAT	mat	mat	The intake air temperature in °F or C, depending on your settings.
CLT	coolant	clt	The coolant temperature in °F or C, depending on your settings.
Engine	engine	engine	Engine Operating/Status variables - bit fields for "engine" variable. This value will tell you if the engine was accelerating, warming-up, etc., and can be used to troubleshoot by telling you if accel enrichment, warm-up, etc. was active at any given time. Field Bit (decimal value) Values ready: 0 (1) 0 = engine not ready; 1 = ready to run (fuel pump on or ignition pulse) crank: 1 (2) 0 = engine not cranking; 1 = engine cranking startw: 2 (4) 0 = not in startup enrichment; 1 = in startup enrichment warmup: 3 (8) 0 = not in warmup; 1 = in warmup aen: 4 (16) 0 = not in acceleration mode; 1 = acceleration mode den: 5 (32) 0 = not in deceleration mode; 1 = in deceleration mode Here are examples of what some of the various values mean: Note that running and cranking are allowed at the same time, so you will normally see 3, not 2, while cranking.
Gego	egoCorrection	egocor1	This is the percentage correction to the fuelling pulse width used to adjust the pulse width calculated from the fuelling equation based on EGO sensor feedback.
Gair	airCorrection	aircor	This is the percentage correction to the fuelling pulse width used to adjust the pulse width calculated from the fuelling equation based on intake air temperature (IAT) density correction and the ideal gas law.
Gwarm	warmupEnrich	warmcor	This is the warm-up percentage correction to the fuelling pulse width used to adjust the pulse width calculated from the fuelling equation based on coolant temperature (CLT) and the warm-up enrichment table (WUE).
Gbaro	baroCorrection	barocor	This is the barometric pressure percentage correction to the fuelling pulse width used to adjust the pulse width based on the user's setting for baro correction (2-point, table; start-up, real-time, etc.).
Gammae	gammaEnrich	gammae	This is the 'net' percentage correction to the fuel pulse width from the other gammas - air density, warmup and barometric corrections (but not including accel enrichments).
AccelEnrich	accDecEnrich	tpsaccel	This is the 'net' correction (in milliseconds) to the fuel pulse width of accel enrichments, including TPSdot, MAPdot, and X-Tau, where used.
Gve	veCurr1	vecurr1	This is the current interpolated VE value used for the fuelling equation for injector driver #1 (and #2 if not using dual tables), based on the current rpm and MAP value (or alpha-N conversion table, where appropriate).
PW	pulseWidth1	pw1	This is the injector pulse width time in milliseconds (including the opening time) for injector driver #1 (and injector driver #2 unless you are using the dual table option).
DutyCycle1	dutyCycle1	computed by TunerStudioMS	This is the duty cycle of injector driver #1 (and injector driver #2 if dual tables option is not selected). The duty cycle is the percentage of the time available that the injector is opening or squirting. Values over 100% are not physically possible, and indicate that the settings in TunerStudioMS exceed the capabilities of the injectors (which may be too small).
Gve2	veCurr2	vecurr2	This is the current interpolated VE value used for the fuelling equation for injector driver #2 if using dual tables, based on the current rpm and MAP value (or alpha-N conversion table, where appropriate).
PW2	pulseWidth2	pw2	This is the injector pulse width time in milliseconds (including the opening time) for injector driver #2 if you are using the dual table option. Otherwise it has no meaning.
DutyCycle2	dutyCycle2	computed by TunerStudioMS	This is the current interpolated VE value used for the fuelling equation for injector driver #2 if using dual tables, based on the current rpm and MAP value (or alpha-N conversion table, where appropriate).
SparkAdv	advance	adv_deg	The spark advance as seen at the crank shaft, including the all the factors such as trigger offset, spark table value, temperature corrections, etc. It is what you should see on a timing light, if you have set everything up correctly.
knockRet	knockRetard	knk_rtd	This is the current amount of ignition retard being subtracted from the spark advance table 'look-up' value when knock is detected. It is determined from the user inputs.
ColdAdv	coldAdvDeg	cold_adv_deg	This is the current amount of ignition advance being added to the spark advance table 'look-up' value advance when the coolant temperature is low. It is determined from the user inputs.
Dwell	dwell	coil_dur	This is the actual computed dwell output, including all corrections. Does not apply to Ford EDIS.
tpsDOT	tpsDOT	tpsdot	This is the current rate of change of the throttle position sensor - TPS - output (%/sec).
mapDOT	mapDOT	mapdot	This is the current rate of change of the manifold absolute pressure (MAP) sensor output (kPa/sec)
IAC	iacstep	iacstep	This is the current position (number of steps) of the stepper motor from the fully retracted position.
deltaT	deltaT	dt3	The time delta (interval, aka. ΔT) between rpm pulses in microseconds. It is the time between skip teeth - the processor is interrupted every time a tooth arrives, when it counts 12 teeth, as in your case, it calculates deltaT as the difference between present CPU clock time and the saved clock time 12 teeth ago. It is accurate to within better than a microsecond, because all the times are stored at the time the tooth arrives, even if the interrupt isn't entered until a bit later because there was another interrupt at that instant.
Trigger±	trig_fix	trig_fix	The code for toothed wheels checks for missing or extra teeth and handles them if they occur, but only allows one or 2 corrections in a row. More than two corrections and it re-synchs. The code works like this: when a tooth input arrives, the code checks the new time between teeth against the previous time between teeth. The processor compares the time between teeth = present time - last tooth time, with the previous time between teeth. If the new tooth time is within PulseTol % of the old, it is accepted. If it is out of tolerance too long, the trigger± counter counts down (missing tooth), if too short it counts up (extra tooth). Account is taken of whether it is time for the missing tooth, so the counter is not changed in this case. Also, if 1 tooth is missed, it adds in a virtual tooth, and if there is an extra tooth it ignores it. But it only does this one time in a row, then the next time between teeth must be in tolerance or the ignition input resynchs. However this cycle can repeat indefinitely as long as there is a good tooth after the bad tooth. This will tell users when they have noise or weak signal issues. When trigger± counts down it means that it is losing tooth pulses, that is,a pulse is coming in much slower than the previous two, as if there were a missing tooth, but the missing tooth is not where its supposed to be. If this only happened once in a great while, the ECU would insert a tooth and keep going, but if it happens twice in a row it declares resynch (and forces rpm to 0), then it waits to get two regular teeth, then looks for the missing tooth, etc. It works like this precisely because the timing can get very screwed up if the controller were to keep putting in teeth, so there is a lot of error checking and if things don't look right, the safest course is to resynch. When it resynchs the timing goes back to normal, so at worst you might miss a tooth, go back to sync, miss a tooth, etc, but you won't end up 180° out of time. If trigger± counts up, it means the controller is seeing noise, that is extra teeth that don't really exist. It discards these extra teeth signals.
Sync Stat	synch	synch	This is the sync status.
tachCount	tachCount	tachCount	Counts tach pulses for use in correlating datalog values with tach pulses (at low rpm).
XTau1	xTauFuelCorr1	XTfcor0	This is the current X-tau fuel correction for injector driver #1 (and injector driver #2 if not using the dual table option).
XTau2	xTauFuelCorr2	XTfcor1	This is the current X-tau fuel correction for injector driver #2 if using the dual table option.
E85fuelCorr	fuelCorrection	fuelcor	This is the current fuelling correction based on the fuel composition sensor feedback and the flex fuel settings.
Ethanol%	fuelComposition	computed in TunerStudioMS from default values	This is the current calculating ethanol percentage in the fuel based on the flex fuel sensor feedback.
AFRtrgt1	afrtgt1	afrtgt1	This is the current target value from the AFR table for the current operating conditions (rpm and MAP kPa).
knck-V	knock	knock	This is the current knock signal voltage.

Note that there are a number of other items that could be included in a datalog, these are shown in the [OutputChannels] section of the INI.

• Start Logging (Alt-L) - starts a datalog. The runtime values will be saved to a file once you give the file a name. A default name is 'suggested' by TunerStudioMS, and has the format 'datalogyyyymmddhhiii.msl' (or .xls), where: 
  • yyyy is the year,
  • mm is the month (0-12),
  • dd is the day (0-31),
  • hh is the hour (0-24), and
  • ii is the minute (0-59),
  all based on the time of creation of the datalog. The frequency of the datalog is set in the 'Timer Interval (ms)' of the Communications dialog.
• Stop - stops the datalog from recording additional runtime variables.
• Burst Logging Mode datalog at the maximum speed the comm port will support, regardless of the timer interval set in the communications settings. This will result in very large datalog files in very short periods.
• Import/Conversion-
• View With MegaLogViewer-

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This will close TunerStudioMS.

• General

  On the main TunerStudioMS menu is an item called 'Settings/General'. You can set these as follows:

  • ECU Type: This should be set to match the ECU you have, either 1 for MS-II, or 2 for MicroSquirt. Note that for 2.88 Code, the first thing you must do is set the ECU Type (under 'Fuel Set-Up/General') to match your hardware (MS-II™ controller, MicroSquirt® controller, or Sequencer™ controller), TunerStudioMS will not let you change anything else until you do this. ECU Type setting was inserted to head off the potential MicroSquirt^® problems due to the coils being turned on with the old default configuration. As of the 2.88 code, if ECU Type is not set, the code will put the ignition outputs in a safe state (cycling the rpm from 0 to 8000 rpm, and also flashing the fuel pump LED) and wait until a known ECU type is put in by the user.
  • Engine Displacement: The engine's displacement in cubic inches, it was put in to be able to convert MAF values to MAP values, so as to keep consistent units everywhere.
  • Manifold displacement: This is the manifold's interior volume (in cubic centimeters = milliliters) for use in the air modeling algorithms. It is only used if model based calculations (with a MAF+MAP sensor) are chosen as a fuelling algorithm under 'MAF vrs. MAP Usage → Enable MAF Use'.

    It includes the runner volume plus any plenum volume. You can measure this by removing the manifold and measuring the amount of water it takes to fill it.

    If you don't want to measure the manifold, and it is a fairly standard configuration, the default is 2400 cc's; and this is for a typical V8 single plane 'spider-style' manifold. For a 4 cylinder engine, you might use ½ this value (1200 cc), and for a 6 cylinder you might use 1800 cc).

  • Compression Ratio: This is the engine's mechanical compression ratio, computed by dividing a cylinder's (swept volume + clearance volume)/clearance volume. This is used in the model based algorithm.
  • Injector Flow Rate: This is the steady state fuel flow rate of injectors in grams per second (grams/second). Injectors are usually rated in pounds per hour of gasoline, or cubic centimeters per minute.

    There are 453.6 grams in a pound, and 3600 seconds in a hour, so if you are using gasoline:

    grams/second = (pounds/hour) × 453.6 ÷ 3600 = (pounds/hour)/7.936

    For cc/min, one milliliter of gasoline is roughly 0.737 grams. 1 cubic centimeter (1 cc) equals 1 milliliter (for example: 5000 cc = 5000 milliliters = 5.0 liters). The density of gasoline is 0.737 g/mL and there are 60 seconds in a minute, so:

    grams/second = (cc/min) × 0.737 ÷ 60 = (cc/min)/81.41

    Here is a calculator to help with the conversion of the usual injector flow rates to grams per second as used by MegaSquirt^® controllers:

    Inputs:     Injector Flow (for gasoline):   lb/hr cc/min Fuel: Gasoline (0.737g/mL) E85 (0.780 g/mL) Ethanol (0.789 g/mL) Methanol (0.791 g/mL) Nitromethane (1.137 g/mL) Toulene (0.867 g/mL) Xylene (0.864 g/mL) Result:     Injector Flow Rate (fRate) setting for ECU: grams/sec (g/s)

  • Injection Timing Delay (InjStart): This is a user input in percentage after tach pulse that tells the controller when to start an injection event (i.e. a 'squirt'), and users can tune this to optimize the injection timing. Injection Timing Delay is a value that is a percentage of the number of degrees between injection events. Valid numbers are between 0 and 100 percent.

    ANY NUMBER LARGER THAN 100 WILL PREVENT THE INJECTORS FROM FIRING. You must use a number LESS than the values below.

    To convert the injector timing delay from the percentage used to crank degrees, multiply the injector timing delay percentage by these numbers:

    • 90° for a 4 stroke V8,
    • 120° for a 6 cylinder/4-stroke (even fire),
    • 180° for a 4 cylinder/4-stroke.

    So a value of 40% on a 6 cylinder gives an injection delay of 40%×120° = 48°. The injection will then occur at 48° after the tach event, or 48° - trigger offset (btdc).

    Note this is a variable for injection start angle relative to the tach pulse (not necessarily TDC). The start of the fuel injection pulse width will begin at:

    Tach time + InjStart % × predicted delta_t (between present and next tach pulse)

    which is in crank degrees. When that time is exceeded in the main loop, MAP is grabbed, the pulse width is calculated, and fuel is injected in that sequence.

    Now because MegaSquirt^® does not do sequential injection (though the MS-II will), it won't squirt at the same point in the engine cycle for all the cylinders connected to the same injector driver, but by moving the injection timing delay around you may be able to improve your idle. There is no simple calculation to come up with the best number for you to use. The general idea is to avoid injecting into an open exhaust valve. Since MegaSquirt^® controllers use a banked injection system, then it would be better to move the timing on all the cylinders to a place where it avoids this on all cylinders (or as many as can be accommodated).

    What you have to do is adjust the injection timing delay from 0% to about 80% and see which value gives you the best idle - as determined by the highest vacuum, or leanest AFR, or smoothest idle, or whatever else you are tuning for.

    Of course there is a limit - you can't inject at say 98% of the next predicted tach pulse interval because there may not be time to calculate it all. Plus there is bit more fluctuation in fuel timing - NOT in the overall fuel pulse width, which will still be interrupt driven and exact, but in when the injection starts. This could vary by as much as a few milliseconds at low rpm, but the idea is that it is way better to inject within ± a few ms of optimum than to consistently inject at a non-optimal value.

    However, to ensure there is plenty of time to calculate the PW and start the injection, the fuel start time is limited to force it to occur at least 2 ms before the predicted next tach pulse. So if you look at a scope you will see the fuel pulse move right relative to the tach input as you increase InjStart %, but it will stop when it gets within 2 ms of the next tach in pulse, regardless of your increasing InjStart %.

  • Dual Table Use choose whether you want to control each bank of injector independently, or to run both injector banks off one set of VE/AFR tables.
  • Barometric Correction choose whether you want:
    • 'None' - no barometric correction,
    • baro correction based on the initial start-up MAP reading ('Initial MAP Reading'), or
    • 'Two Independent Sensors' for continuous baro correction (ONLY if you have installed a second MAP sensor.)
  • X-Tau UsageX-Tau usage can be set to off, or accel/decel using this parameter. The X-Tau tuning values are set in the X-Tau Time Table menu item under Tables. See the X-Tau page for more information.
  • Prime, ASE, WUE Tables. Chose whether you want two point (a high temperature and a low temperature settings) or 10 entry tables for the prime pulse, afterstart enrichment, and warm-up enrichment. The tuning values for tables are listed in under the menu item Tables. Note that switching from 2-point to tables (or vice-versa) does NOT transfer your settings! For example, if you started out with values optimized for your application of 6.0 and 1.8 in the cranking pulse widths, if you then switch to 'tables', the cranking pulse width values will be the much larger defaults, and not a function of the 6.0 and 1.8 you originally entered. So be sure to check ALL the tables (or 2-point values, if going to 2-point) for appropriate values if you change this setting.
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• Idle Control

  The basic idea of IAC is that the motor or PWM solenoid starts out with a large opening of the air valve at cold startup, then gradually closes as the coolant temperature rises. The basic motor position at any given time is determined from the input table of step position versus coolant temperature. To this basic control algorithm, several features have been added as described below. You need to set MegaSquirt-II to tell it if you have a fast idle "solenoid type" valve, a PWM type valve, or a stepper motor IAC, or none of these. These are selected under Settings/Idle Control in TunerStudioMS:

  • Algorithm (IdleCtl): If you have a:
    • On/Off Fast Idle Valve (FIdle): Set the algorithm to 'Solenoid'. You can also set your Fast Idle Threshold if you have installed a fast idle solenoid. Enter a coolant temperature to turn on the fast idle solenoid. A typical value is 145° Fahrenheit. The Fast Idle valve will be activated below this temperature (145°F) and turned off above 145°F. The Fast idle Threshold is independent of any warm-up enrichment. Fast idle valves generally have one or two wires.
    • Idle Air Controller (IAC): If you have a stepper motor IAC, you can set the IAC Start position, as well as ten intermediate positions based on the coolant temperature to allow a decreasing amount of "extra air" as the engine warms up. These are set under 'Tables/Idle Steps' in TunerStudioMS. Stepper motor IACs usually have four wires.
      • IAC Stepper Moving Only: Powers the stepper only when changes in pintle position are requested. This is the most common type, it holds its position if not powered, and is difficult to turn by hand.
      • IAC Stepper Always On: Powers the stepper at all times. Required if your stepper 'free wheels' when you spin its pintle un-powered with your hand.
      • PWM Warm-Up: This is pulse width modulated warm-up, such as with the Ford PWM idle valves. You need to make modifications to use this with MS-II, see: www.megamanual.com/ms2/IAC.htm#pwm
      • 15-minute IAC: Operates the stepper IAC as 'always on' for 15 minutes, then switches to 'moving only'. This is sometimes helpful if your IAC operation is erratic.
  • Fast Idle Temperature: The temperature at which to switch off the solenoid type idle valve.
  • Time Step Size (ms) (IACtstep): IAC stepper motor nominal time between steps.
  • Acceleration Step Size (ms) (IACaccstep): not currently used.
  • Minimum Steps to Move: This command is used to move the stepper IAC a minimum number of steps so that it isn't 'jiggling' between steps and potentially loosing count.
  • PWM Frequency (Hz) (PWM_step): This is the PWM frequency in Hertz (cycles per second) used for the PWM Idle valve, when it is enabled. The PWM frequency can only be adjusted in steps of 80 Hertz, from 80 Hz to 800 Hz.
  • Start Value (IACStart) - changes requires an MS-II reboot : This is the number of IAC steps the pintle is retracted to the 'wide-open' position when MegaSquirt^® is powered up. It is used at all temperatures.
  • Cranking Position (IACcrankpos): During cranking, extra air may be useful in the same way as extra fuel in cranking pulses. The table value for the starting temperature may be fine after the engine has started up, but during cranking more power may be needed, especially if the starting temperature is cold. To provide this, you can input a step position that provides a larger than normal air opening during cranking. So, if in cranking and 'Cranking Position' < table value, then the IAC motor position (or PWM%) is set to 'Cranking Position', and when cranking is done, the motor position starts tapering (over the 'crank to run taper time') up to the table value over a user input period, typically a few seconds. (See the diagram below) If this feature is not desired, Just set 'Cranking Position' to a value higher than any table value. Then the table value will always be used since it provides more opening.

  • Crank-to-Run Taper Time (IACcrankpos): This is the time over which the cranking position of the idle (either the stepper steps or the PWM%) is moved to match the table value (see diagram below). Higher values give a higher idle for longer periods, which can improve starting performance.

  • Hysteresis (°) (IdleHyst): Hysteresis is a general term used in control applications. It refers to the amount something must change before something else will change (usually the amount an input must change before an output is adjusted). In MegaSquirt-II IAC control, the hysteresis refers to the amount the temperature has to change before the stepper motor is moved to the new calculated position.

    So, for example, if the motor last moved at 140°F, and the hysteresis is set to 5°F, then it won't move again until the temperature reaches 145°F. The setting prevent from moving the motor back and forth constantly, heating it unnecessarily.

    A value from 5°F to 10°F is good for most installations. This input can be used to avoid continuous motor motion (and wear) for small coolant temperature changes and random 'jitter' in the coolant temperature signal . Changes to the motor are only made when new coolant temperature > coolant temperature on the last move, or, new coolant temperature < (coolant temperature on the last move - Hysteresis temperature). What this does is allow constant motor motion while the coolant temperature is rising, but when it peaks, there will be no further motion unless things cool back down - which is unlikely.

  • Time Based Afterstart: No one should use the Time Based After Start (extended warmup) option unless they need it, and very few will. Disable it by setting the 'cold temperature to -40°F. Time based option is meant to operate as follows: it only is used if the starting temp (at power on) is < Cold Temperature, and Cold Temperature should be fairly cold. (Set to -40 or less to get rid of the option, which 90% of people don't need.) Then, the car and idle valve operating normally during the warm-up until you get to the Cold Position PWM value, say 80% of fully closed. That is where you would typically switch to the time-based, and the reason is that if it continues to taper the coolant normal operating temp, SOME cars (very few) continue to need a fast idle (possibly due to heavy oil which is nowhere near at operating temp when the coolant gets there, plus a hot cam with not enough idle torque to overcome the oil drag). So starting from the 80% closed position you taper to fully closed over a span of maybe a minute or even 5 minutes. The car should never start with a idle PWM table value > Cold Position unless the start temperature is > Cold Temperature, in which case time based won't be used.
    • Cold Temperature (°) (IACcoldtmp): This defines the initial coolant temperature below which the afterstart taper will be extended, based on the Cold Position and Cold Taper Time. It should be set fairly cold, generally not more than 20° F.
      
    • Cold Position (steps) (IACcoldpos): The Idle PWM values at which time based afterstart tapering is initiated. Note that this value must be higher than the lowest value in your IAC PWM table, or you can get strange operating results.
      
    • Cold Taper Time (sec) (IACcoldxt): This is the number of seconds that MegaSquirt^® takes to move from the 'cold position' to the position indicated in the IAC step table for the current coolant temperature.
      
  

• Port Settings The general purpose I/O logic in MegaSquirt-II code version 2.3 (and above) allows for using the following seven pins as 'spare' outputs:
  • FIdle - PM2 (DB37 pin #30),
  • LEDs (x3),
    • Injection LED - PM3,
    • Accel LED - PM4,
    • Warm-Up LED - PM5.
  • IAC1,2 these are capable of driving over 0.5 Amp, sufficient for most automotive relays,
    • IAC1 - PT6,
    • IAC2 - PT7.
  • Knock Enable - PA0.

  The two spare port "T" pins (PT6 and PT7) are normally used to drive the stepper motor chip (IAC1,2). When you set pin PT6 high, it will make 1 of the 4 stepper output pins high and the other low, and no effect on the last two - which are controlled in the same way by pin PT7. So, by picking 2 of the 4 IAC outputs, you have two 12V spare pins that will directly drive about 0.5 Amps with no transistor needed. This is more than enough to drive a relay directly. If you are going to use port PT6 or PT7 as spares (IAC1,2), IdleCtl should be set to 0. This will keep the the stepper chip 'always enabled' and not turn it on and off, which would prevent the port from working as intended.

  The pin on/off commands are set by pointers. When a user wants to use say an LED as a spare output, then the pointer is set to point to a dummy register in RAM (random access memory), and that's it. It's just like setting a jumper on the PCB to route a signal one way or another.

  The spare pins have generic logic based on the values of up to two of the real time display variables. The user can specify these in TunerStudioMS and they will be passed to MegaSquirt-II as offsets. The user can also specify:

  • Variables:
    • rpm,
    • MAP (manifold absolute pressure),
    • tps (throttle position),
    • clt (coolant temperature),
    • etc..
  • Threshold values,
  • Conditions:
    • 'less than' (<),
    • 'equal to', or (=),
    • 'greater than' (>).
  • Pin set value (whether the pin should go high (5 Volts) or low (ground) when the conditions are met), and
  • Hysteresis deltas (the amount the variable must change before the pin set value can be reset). The inclusion of a hysteresis factor is important to prevent the device from switching on and off rapidly at the set point due to slight fluctuations (or noise) in the sensor signal. Rapid fluctuations can rapidly wear out relays and other electro-mechanical devices,
  • And combine two conditions with:
    • AND ( & ) - meaning both conditions need to be satisfied,
    • OR ( | ) - meaning the pin is activated if either condition can be satisfied, and
    • blank ( ' ' ) - meaning the first condition only is used.
  Note that you may have to use the tab key after entering values to get them to 'stick'.

  (See this link for more information and examples.)

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• Injector Characteristics
   
  • Injector Opening Time (ms) (InjOpen) is the amount of time required for the injector to go from a fully closed state to a fully opened state when a 13.2 volt signal is applied. Since fuel injectors are electro-mechanical devices with mass, they have latency between the time a signal is applied and the time they are in steady-state spraying mode. Typically, this value is close to 1.0 milliseconds. Note that the closing time should theoretically be subtracted from the opening time, but the closing time is generally very small compared to the opening time.
  • Battery Voltage Correction (ms/V) (BatFac) is the number of milliseconds that MegaSquirt-II adds to each fuel injection pulse to compensate for the slower opening of the injectors with lower supply voltages. Generally 0.10 ms/V or 0.2 ms/V is about right. So, with a 0.20 Battery voltage correction factor and supply voltage of 14.5 Volts, a 1.0 millisecond 'opening time' is adjusted to 1.0 - (14.5-13.2)*0.20 = 1.0 - 0.26 = 0.7 milliseconds.

    Conversely, If you had injector specs that stated the opening time was 0.7 milliseconds at 14.5 Volts, and your battery correction was 0.20, then you should enter 1.0 as the 'Injector Opening Time'.

  • PWM Time Threshold (ms) (InjPWMTim) is the amount of time the Pulse width has to be on before PWM starts. This allows full voltage to reach the injectors while opening. Generally you should set this to the same value as your injector opening time (~1.0 millisecond)
  • Injector PWM Period (µsec) (InjPWMPd) - changes requires an MS-II reboot - This is the time between cycles of on/off and the Injector Duty Cycle is the % of time it stays on relative to the total time for one cycle. You use high frequency to make things smooth. Since the injectors stay open for milliseconds, you need a period that is much shorter than that. Such a frequency never lets the injector start to close - the turn off turn on cycle is so fast that the injector stays where it is. Keep this value between 10 and 25 kHz (100-40 µsec). Generally, use the default, unless you have determined another frequency is optimal.

    The optimal PWM current limit frequency is correlated with the inductance of the injector, resistance of the loop, and elapsed time/duty. The goal is to switch the injector current on and off without an appreciable change in *average* injector current - the current which holds the injector open. Faster PWM frequencies mean less current deviation. But since the injector is already held wide open (or should be) a faster PWM frequency will not hold it open any more than it already is.

    A overall PWM setting above several kiloHertz (kHz) works based on most automotive injectors, and there is no advantage of running the frequency higher. In fact the higher switching will require a little more heat dissipation. Electromagnetic interference (EMI) with other circuits on MegaSquirt^® is also an increasing possibility as frequency rises.

    If you want to calculated the optimal period, then measure the injector inductance, and run it through the relation for inductor current:

    I = (E/R)×(1-e^-tR/L)

    When the inductor is charging, use the battery voltage for E, and when it is discharging use the voltage drop across the PNP Darlington, about 1.5 volts. You can then see the amount of current deviation based on PWM frequency.

    If you want to measure this directly, install a low value resistor (like 0.05 ohms) in series with the injector and monitor the voltage drop across the resistor with a scope. You will then see the hold current and the deviations cased by frequency.

  To tune the PWM [pulse width modulation] percentage and time threshold values for your engine, you need to know what kind of injectors you have: low-impedance or high-impedance. If you are running high-impedance injectors (greater than 10 Ohms), then set the PWM time to a number like 25.4, in essence you are disabling the PWM mode. This allows full voltage to the injectors throughout the pulse width. For low-impedance injectors (less than 3 Ohms), you need to limit the current to avoid overheating the injectors. To do this, there is a period of time that you apply full battery voltage [peak] current, then switch over to a lower current-averaged [hold] current, i.e. peak and hold.

  Alternatively, you can add resistors in series with the injectors. See the Injectors and Fuel Supply section of the MegaSquirt^® manual for more details. To run low-impedance injectors with the PWM current limit mode, you need to set two parameters - the "PWM Current Limit %" and the "Time Threshold for PWM Mode" - both are on the "Constants" page. The current limit % is the percent duty cycle when the current limit is invoked. The time threshold is the amount of time from when the injector is first opened until the current limit is activated.

  High impedance injectors can run on 12 Volts without problems. Low-impedance injectors require some form of current limiting. MegaSquirt^® has pulse width modulation to limit the current. You need to set the PWM parameters to match your injectors:

  • If you are running high-impedance injectors (greater than 10 Ohms), then set the:
    • PWM Time Threshold to 25.4 msec, and the
    • PWM Current Limit (%) to 100%.
    (The presence or absence of the active flyback circuit (v3) or flyback board (v2.2) doesn't matter for high impedance injectors.)

  • If you have low impedance injectors (less than 4 Ohms), set the:
    • PWM Time Threshold to 1.0 msec, and
    • PWM Current Limit to 30% in most cases (all V3 main board with active flyback installed, and all V2.2 main board with flyback daughter board installed).

      Set the initial PWM% to 75% if and only if you have you impedance injectors and have NOT installed:

      • the active flyback circuit on a V3 main board (assembly manual step #69), or
      • the 'Flyback Board' daughter card on a V2.2 main board).

  You will tune these after getting the engine running.

  See 'Setting the PWM Criteria' in the tuning section of the MegaSquirt^® manual.

  Failure to perform the tuning steps can result in damage to your injectors. If you have high-impedance injectors, set these values to 25.4 ms and 100%, and you do not need to tune them further.

  Return to help index

• Injector Control
  • Required Fuel Engine Displacement
    The total swept displacement of your engine (more precisely, the air that your engine would pump in a single cycle at 100% VE). Nothing tricky here, just tell TunerStudioMS how big your engine is.
    • Injector Flow
      The nominal flow rate of your injectors at the fuel pressure that you will run. If you have a flow rating in cc/min divide it by 10.5 to get lbs/hr (this assumes a specific gravity of 0.70 for the fuel). If your flow rating is at a different pressure (say they are rated at 43.5 psi and you will be running 50 psi), use the following equation to compute the flow rate at the new pressure:
      newRate = oldRate * sqrt(newPressure/oldPressure)
      So for our example, assume we have 550 cc/min @ 43.5 psi injectors we wish to run at 50 psi: 550 * sqrt(50/43.5) = 589 cc/min
    • Air Fuel Ratio
      The stoichiometric mass ratio for the fuel you plan to use with the MegaSquirt^® controller. For gasoline, this should be 14.7:1. Stoichiometric mass ratios for other fuels are given in the table below, but be aware that they all have very different density than gasoline, so the injector flow rate will be different, too.

      Fuel	AFR
      Methanol	6.4
      Ethanol	9.0
      Gasohol (10% ethanol)	14.2
      Gasoline	14.7
      Propane	15.7

    For more info, see: What is stoichiometric?
  • Control Algorithm can be 'Speed density (using a MAP sensor, rpm, and intake air temp. to calculate fuel), Alpha-N (ignoring MAP, and using the rpm, throttle position sensor, and intake air temp. to calculate fuel), or Hybrid Alpha-N.

    With Alpha-N, you fill in a 6x6 table ('Other Tables/Alpha_N MAP table') that defines how the TPS is translated into a 'faked' MAP kPa that is then used with the 12x12 VE table.

    So the ECU uses the TPS to look up the MAP in the 6x6 table (which should have TPS% ranging from 0% to 100%), then uses that to determine the fuelling based on the VE table. The advantage is that you can use different fuelling at different rpms (it also makes the blended MAP/alpha-N options possible).

  • Injection Per Engine Cycle This is the number of times per engine cycle (2 revolutions for a 4-stroke cycle engine, one revolution for a 2-stroke cycle engine) that MegaSquirt^® will fire the injectors. (It is often referred to as the 'number of squirts'.) If you choose alternating for port injection, make sure your number of squirts is an even number (2,4,...) and evenly divisible into the number of cylinders. For example, with an eight cylinder engine, you could use alternating and 2, 4, or 8 squirts/cycle. With a six cylinder, if you choose alternating, you MUST use 2 or 6 squirts/cycle.
  • Injector Staging can be either simultaneous (both injector drivers fire at once), or alternating (one injector driver fires on one injection event, the other fires on the next, and so on; 'ping-ponging' back and forth). If you choose alternating for port injection, make sure your number of squirts is an even number (2,4,...) and evenly divisible into the number of cylinders. For example, with an eight cylinder engine, you could use alternating and 2, 4, or 8 squirts/cycle. With a six cylinder, if you choose alternating, you MUST use 2 or 6 squirts/cycle. Also, the only possible combinations for an odd-cylinder count engine are either 1 squirt/simultaneous or N squirt/simultaneous combination, where N is the number of cylinders."

    Permissable Combinations: Number of Cylinders
    		1	2	3	4	5	6	8	10	12
    	1	OK	simultaneous only	simultaneous only	simultaneous only	simultaneous only	simultaneous only	simultaneous only	simultaneous only	simultaneous only
    	2	no	OK	no	OK	no	OK	OK	OK	OK
    	3	no	no	simultaneous only	no	no	simultaneous only	no	no	simultaneous only
    	4	no	no	no	OK	no	no	OK	no	OK
    	5	no	no	no	no	simultaneous only	no	no	simultaneous only	no
    Number	6	no	no	no	no	no	OK	no	no	OK
    of	7	no	no	no	no	no	no	no	no	no
    squirts	8	no	no	no	no	no	no	OK	no	no
    	9	no	no	no	no	no	no	no	no	no
    	10	no	no	no	no	no	no	no	OK	no
    	11	no	no	no	no	no	no	no	no	no
    	12	no	no	no	no	no	no	no	no	OK

    "OK" means the combination will work with either simultaneous or alternating. "no" means it will not work with either, i.e., not at all.

    There are a number of considerations in choosing the number of squirts:

    • Throttle body injection (TBI) and port injection are completely different in regard to the required number of squirts - so this must always be taken into account. TBI often requires at least half the number of squirts as cylinders fed by the common plenum (ex.)
    • Increasing the number of squirts alone increases the accel enrichment (since the accel enrichment is per squirt),
    • The timing of the injection (the 'injection timing delay' under 'Fuel Set-Up/General') can make a big difference to how sensitive the engine is to the number of squirts (since with fewer squirts you might be squirting into the disrupted airflow of the overlap period at low speeds).

    More squirts are more likely to help if the engine:

    • has a low idle rpm,
    • is tuned to relatively lean (ex. stoichiometric or leaner) idle mixtures,
    • has high idle advance (say more than 15° to 20° BTDC),
    • wants larger accel enrichments.

    However, if the engine is tuned so that the idle MAP is minimized (likely 13.5:1 AFR or so), and has a higher idle speed (say 800 rpm compared to 600 rpm), then more squirts is less likely to help.

    There are definitely some down sides to more squirts:

    • More squirts makes the tuning more sensitive to the correct opening time, and this is one of the harder things to determine accurately.
    • More squirts reduces the effective resolution of the req_fuel, accel enrichments, etc. (since they are adjusted in 0.1 msec steps, but on increasingly short pulse widths)
    • As well, more squirts eats up more of the available time with open/close cycles, reducing the dynamic range of the injectors. So users who have chosen their injectors based on the net horsepower may find they are too small at high rpms and loads. This can damage an engine, and must be avoided at all costs, of course.

    So more squirts may help. They may not, however. And this can be a bandage for poor idle or accel tuning. So users should start with 2 squirt/alternating for port injection, and tune it as well as they can.

    Then, if they can't solve some issues, they should try more squirts. But jumping straight to more squirts is probably not a good idea - most often it just masks the need for a richer idle mixture or more accel enrichment.

    Example: Suppose you have a 4 cylinder 4-stroke engine. Then in 720° (two revolutions) you have 4 spark events (at 0°, 180°, 360° and 540°, then starting over at 720°=0°). MegaSquirt can only inject on an ignition event, so 1, 2, or 4 squirts/cycle for this engine. If you have 2 squirts/simultaneous, you have: crankshaft degrees  0°  90° 180° 270° 360° 450° 540° 630° 720° =0° ...→ cylinder 1 3 4 2 1 ...→ bank 1 inject inject inject ...→ bank 2 inject inject inject ...→ but with 2 squirts /alternating, you have: crankshaft degrees  0°  90° 180° 270° 360° 450° 540° 630° 720° =0° ...→ cylinder 1 3 4 2 1 ...→ bank 1 inject inject ...→ bank 2 inject ...→ Both are two squirts per cycle, but alternating only has 1/2 as many total squirts per injector (i.e., since only one channel is active per squirt), so the pulse width must be doubled. 4 squirts/simultaneous would look like this: crankshaft degrees  0°  90° 180° 270° 360° 450° 540° 630° 720° =0° ...→ cylinder 1 3 4 2 1 ...→ bank 1 inject inject inject inject inject ...→ bank 2 inject inject inject inject inject ...→ There are 4x as many injection events with 4 squirts/simultaneous compared to 2 squirts/alternating, so the pulse width is just 1/4 as long (neglecting the opening times). The req_fuel calculator will show this - watch the top and bottom numbers as you make changes to the alt/sim and number of squirts. The top number stays the same (it is the 'unadjusted number' for 1 squirt simultaneous), while the bottom 'adjusted' number used for the pulse width calculations changes with the number of squirts and simultaneous/alternating.

  • Engine Stroke is determined by whether your engine is a two-stroke cycle engine (mostly small motorcycle and marine engines for gasoline) or four stoke-cycle (most automotive engines).
  • Number of Cylinders
    This is the number of cylinders in your engine, used to divide the engine displacement above to compute mass of air per cylinder at 100% VE. If you have set the number of cylinders in the Constants window, then this value will be copied into the Required Fuel dialog. If you have not set it in the Constants, then the value you set here will be copied from Required Fuel dialog to the Constants dialog.
  • Injector Port Type is either 'Port Injection (one injector for each cylinder, cylinders don't share fuel), or throttle body (each cylinder can get fuel from more than one injector, typically the injectors are mounted above the throttle).
  • Injectors is the total number of injectors.
  • Engine Type can be 'Even Fire' in which the sparks occur at the same interval through a cycle, or 'Odd Fire' in which the sparks occur at varying intervals (odd fire is typically only found on V6s with 90° bank angles). This option is not enabled in MS-II/3.8xx code, which is for even fire engine only (unless using dual spark).

• Rev Limiter Settings
  • Algorithm - you can select:
    • None - no rev limiter
    • Spark Retard - This option reduces the engine's power by retarding the ignition advance, singaling the driver to shift.
    • Fuel Cut - reduces revs by eliminating fuel. Fuel is initially cut at 'Upper Rev Limit', and fuelling is not restored until the rpm drops to the 'Lower Rev Limit'.
    • Soft Fuel Cut - This starts randomly cutting fuel to the cylinders starting at 'Lower Rev Limit', with complete fuel cut by the 'Upper Rev Limit'. It is less harsh in practice than a plain fuel cut.
  • Maximum Retard is the MOST the spark can be retarded in spark Retard mode,
  • Lower Rev Limit is the level at which the the fuel is re-enabled in Fuel Cut mode, and the level at which timing is fully restored in Spark retard mode.
  • Upper Rev Limit is the level at which the rev limiter is initially applied.

• AfterStart Enrichment: The afterstart enrichment (ASE) is additional fuel for starting that decays from its max value (interpolated from the ASE Hot and Cold Percents and the initial coolant temperature to zero in a linear fashion over a period interpolated from the ASE Hot and Cold Counts when the engine is first started. If the interpolated value for the current temperature is 20% enrichment over 250 ignition cycles, then the first pulse is enriched by 20%, the 125th pulse is enriched by 10% and the 250th (and later) by zero percent (this assumes 1 event per cycle, or a 1 cylinder engine; divide by the number of ignition events per cycle to get the specific behavior for your motor).
  • ASE Hot Start Enable: A hot start is any start where warm up enrichment = 100%. This in turn is set in the warm-up wizard. So if you disable the ASE on hot starts, you get no additional enrichments on starting (and won't flood the engine).
  Two-Point AfterStart Enrich:
  • ASE Cold Percent:
  • ASE Hot Percent:
  • ASE Cold Count:
  • ASE Hot Count:
• Accel Enrich Config
  • AE RPM Scaling
    • Low RPM Threshold: The engine RPM below which the full (non-X-Tau) acceleration enrichment is applied.
    • High RPM Threshold: The engine RPM above which the non-X-Tau accel enrichment is zero.
    • Between the two RPM values, the accel enrichment is linearly scaled from full to zero. For example, if you have values of 2000 and 6000, then ½ the accel pulse width would be added at 4000 RPM (½ way between 2000 and 6000).

  Return to help index

  The after start enrichments (ASE), the warm-up enrichments (WUE), and the prime pulse can be either two-point or tables. You select between them in 'Settings/General'. If you have chosen two point, this is where you set:

  • ASE Hot Percent (%), the percentage of the cold ASE you want applied at the highest temperature in your temperature table, values for the ASE will be linearly interpolated between this and the cold prime value depending on the coolant temp at cranking.

  • ASE Hot Count (cycles), the number of cycles you want the afterstart enrichment (ASE) to last at the highest temperature in your temperature table.

• Additional Fuel, this is a dual function setting, one for adding fuel with nitrous oxide injection systems, the other for use in determining fuel response time.

  Fuel Response Time (cyclic): This is a tool for experimental determination of how a change in fuelling propagates through the system. Additional fuel added (in milliseconds) to normal fuel pulse width for the 'number of injections', which is repeated every 'time between added fuel' in seconds. The idea is that there is a step function in the fuelling (with no other changes). This will help in determining the X-Tau settings, as well as the EGO sensor response time. The amount of time for the EGO sensor to respond to the fuel impulse is dependent on both the transport time (a function of rpm) and the sensor response time.

  Nitrous Control (switched by E0 low): The N2O enrichment input is a percentage which multiplies the Δtime between tach pulses. This provides a fixed fuel flow rate for the constant N2O flow rather than a fixed pulse width. Since the same variable is also used for the fuel response test impulse, which is in milliseconds, a change in the settings.ini file is required if you want to use N2O enrichment.

  You expose the nitrous menu (under 'Other fuel settings/Additional Fuel') by going into the settings.ini file in your project's /mtCfg/ sub-folder and changing the default setting from fuel response determination (#unset n2o) to the nitrous setting (#set n2o):

  find:

  #unset n2o ; choose between n20 enrichment (=set) and PW impulse (=unset) triggered by PE0 (affects menus) 

  and change it to:

  #set n2o ; choose between n20 enrichment (=set) and PW impulse (=unset) triggered by PE0 (affects menus)

  Then whenever PE0 (the JP4 jumper on MS-II™ itself) is pulled low (grounded by the nitrous switch) the specified percentage of fuel will be added (this will work best with a one-stage system, of course!). The specified amount of ignition retard (up to 25.5°) will also be applied.

  Make sure you test this by seeing what it does to the pulse width before you use this with nitrous.

• At Total Vacuum (%): 'At total vacuum' contains the total correction at a barometer reading of 0 kPa.
• Rate (%): 'Rate' contains the percentage per 100 kPa to scale the barometer value.

• Flex Fuel Sensor: Disabled or Enabled.
• Frequency (low) (Hz): The sensor output frequency for 100% gasoline (50 Hz for the GM sensor).
• Fuel Correction (low) (%): The fuelling correction at the low frequency, with GM sensors this is for pure gasoline (normally 100%).
• Timing Correction (low) (deg): The timing to add for pure gasoline (normally 0.0).
• Frequency (high) (Hz): The sensor output frequency for 100% ethanol (150 Hz for the GM sensor).
• Fuel Correction (high) (%): The fuelling correction for the high frequency, with GM sensors this is for pure ethanol (typically 163%).
• Timing Correction (high) (deg): The timing to add for pure ethanol (typically -13°, i.e., subtract 13° of advance when using pure ethanol).

These parameters define the closed loop behavior of MegaSquirt. You must have a either a narrow band or wide band EGO sensor/controller that will work with v3.8 of controller code. To disable closed loop operation altogether, set the EGO Step value to zero.

• EGO Sensor Type
  Specify either a narrow band sensor or wide band sensor. Functionally this merely sets the direction sense of the sensor voltage. For narrow band sensors, the voltage rises as the mixture is richening and drops as the mixture becomes lean. The wide band setting corresponds to the opposite sense, i.e., voltage drops to indicate enrichment (this is how the DIY-WB operates, not necessarily all wide band sensors!). (Available in v 2.0 controller code.)

  Dual Sensors: The dual lambda sensor feature has been in the MS-II code since V1.0. You connect the second sensor to the ADC6 input with appropriate circuitry and it adjusts the PW2 output independently of PW1. You connect the second sensor to the JS5 hole (on a V3 main board) - X7 on a V2.2 main board, duplicating the R10, R11, C10 circuit from the v3.0 PCB in the proto grid area. There is only one calibration because it is assumed you are going to use the same type of sensor on each side. If there is a small difference, you can compensate for it in the separate AFR target tables.

• NB AFR Target (v) (narrow band sensor only)
  This is the switching point voltage that indicates stoichiometric combustion (approximately 14.7:1 with gasoline). For narrow band sensors this is 0.5 v*; for the DIY-WB wideband sensor it is 2.5 v (for other wideband sensors this voltage may be quite different). (This value is only active in v 2.0 controller code.) *This is true for zirconia NB sensors, which are used almost exclusively in modern vehicles. The titania NB sensor has a different voltage range (1-5 v), but is rarely used.
• Ignition Events Per Step (narrow band sensor only)
  This value determines the rate at which the closed loop algorithm applies correction. The default value of 32, when used on a four cylinder engine with four ignition events per cycle, tells MS to wait for 8 cycles before changing the current correction factor.
• Controller Step Size (Percent) (narrow band sensor only)
  Once the closed loop algorithm has decided to change the correction factor, it adds or subtracts this percentage from the current value. This should move slowly to avoid unstable response, so make sure it is small, 1% being the default.
• Controller Authority (%)
  This value limits the correction that can be made by the closed loop algorithm, the default of 10% indicates the correction factor cannot go outside the range 90-110%.
• Active Above Coolant Temp (°F)
  This is the temperature below which closed loop operation is disabled. If this value is too low, then closed loop will try to lean out the warmup enrichments and you may experience rough running. Typical value is 160 F and should somewhat above the point at which warmup enrichment stops (see the Warmup Enrichment Bins settings and find the lowest on which contains 100). The MegaSquirt^® value "EGOTEMP" stores this quantity.
• EGO Active Above RPM
  This value specifies the lower rpm limit above which closed loop operation occurs. Typically, your engine will idle best when it is richer than stoich, so turning off closed loop for low RPM's allows this to happen. The default value for the RPM limit is 1200.
• EGO Active Below TPS (V)
  This value specifies the upper throttle position sensor voltage limit below which closed loop operation occurs. This prevent closed loop operation from leaning the engine out under full throttle. This value is hard coded into MegaSquirt^® (3.5 Volts), user adjustable in MegaSquirt-II.
• EGO Active Below MAP (kPa)
  This value specifies the upper manifold absolute pressure limit below which closed loop operation occurs. This prevent closed loop operation from leaning the engine out under load.

Wide Band Controller Settings

• Algorithm (EgoAlg):
  • Simple: uses a calculated step based on the % difference between measured and target ego.

  • Transport Delay: this waits transport delay seconds before acting on any deviation between the AFR target voltage and the input ego voltage, the exception being when closed loop is first entered, when an immediate correction is made. This is the slow but sure method - unless there is ego jitter that is faster than the transport delay time. The transport delay will be calculated in the program as a function of rpm and map adjusting the constants for this based on the delay.

    From the time the processor commands the injector to open to the time you get a valid feedback from the O2 sensor, the following has to happen:

    1. The fuel has to be combusted and start to exit the exhaust valve. This is not well defined because it depends on the timing of the injection relative to start of exhaust opening.
    2. The exhaust has to travel through the pipes to the sensor. This is a function of map and rpm. The larger map the stronger the explosion, and the faster the rpm the faster the piston pushes out the exhaust.
    3. The sensor has to detect the exhaust mixture. This includes time to measure + averaging time and it should be more or less a constant, probably some function of temperature.
    In addition, you have:
    4. Time from completion of #3 to the start of the next injection. This is because the delay time we are really measuring is the total time between corrections, and corrections can only be made when you inject.

    The control algorithm used in the processor takes into account that there will be a delay between injecting more fuel and getting back a reading and then injecting more or less fuel based on that reading. It can calculate the time between injections, so you don't have to be concerned with that. But it does need the sensor + transportation delay because it has no way of calculating that. If that delay is even the least bit longer than 1 injection cycle, you have to wait for the next cycle to correct.

    The equation used looks like this:

    delay (ms) = Kdly1 + Kdly2*120000 / (map(kPax10)*rpm)

    It assumes you have a measured transport delay at a fixed rpm and map value, e.g, at idle, and you can put the specific rpm, map and measured delay into the equation and you get out a program input (KDly2) needed by the MS II code to approximate the transport delay at any arbitrary rpm and map. Kdly1 is the sensor response delay and include the averaging done by whatever wide band sensor interface system you are using. You could get some idea of the K2 delay by estimating exhaust flow velocity and measuring pipe/ port lengths or by maybe using a spare port to energize a solenoid to squirt a small single shot of extra gas into the intake at a fixed time. You then datalog everything and measure how long it took from the time the solenoid was energized to when the extra gas showed up on the AFR reading. These factors are shown in TunerStudioMS as:

    • Transport Delay 1 (egoKdly1): is primarily the response time of the sensor plus the fastest time between injector and exhaust valve.

    • Transport delay 2 (egoKdly2): is the effect of rpm and map and as well as the exhaust geometry. Note that:
  • PID/Smith Predictor: is a true PID loop with a Smith Predictor correction to mitigate the effects of the transport lag. See: PID_controller for more information.
    • PID Proportional Gain (%) (egoKP): The constant that defines the proportional relationship between the EGO set-point and the range of values seen from the sensor. 100% is a typical value. It defines the response to the immediate difference between the set-point AFR and that measured from the sensor.
    • PID Integral (%) (egoKI): This corrects for a portion of the on-going average correction over time (the integral), allowing the loop to set into a stable value, rather than oscillating. A typical value is 20%.
    • PID Derivative (%) (egoKD): This predicts the future difference between the AFR target and the set-point, based on the rate of change of the error at present. The larger the derivative term, the more rapidly the controller responds to changes in the process's output. However, for relatively slow processes, lower numbers mean more stable output, and a value of 0 is typical for MegaSquirt^® (i.e., don't use the derivative term at all).

• Automatic Mixture Control (AMCOption): (Not for use with MAF-Only Option) Automatic Mixture Control (AMC) allows MegaSquirt^® to adjust the VE table based on the exhaust gas sensor without a laptop computer attached, much like OEM ECUs.
  • Automatic Mixture Control:
    • Disabled: No automatic mixture update of fuelling table(s).
    • RAM Update: automatic updates to RAM VE table(s), changes will be lost on power-down if not saved.
    • FLASH Update: also automatically updates FLASH VE tables.
  • Step Size (%) (AMCStep): % of AMC correction to be applied when RAM VE is updated. A typical value is 10%, this means apply 10% of the change between the old VE value and the adjusted VE value to the VE table(s).
  • Minimum VE Change (%) (AMCdve): smallest AMC VE change that will be applied to the table in RAM, if the change is less than this, it will be ignored (until it reaches the threshold).
  • Vertex Tolerance (RPM) (AMCve_drpm): the furthest that the nearest rpm bin can be away and still have the AMC change applied to that entry.
  • Vertex Tolerance (kPa) (AMCve_dmap): the furthest that the nearest kPa bin can be away and still have the AMC change applied to that entry.
  • Table Change Interval (sec) (AMCramve_dt): is the minimum time (in seconds) between updates of RAM VE table.
  • Flash Update Interval (sec) (AMCT_thresh): is the minimum time (in seconds) between FLASH burns of the RAM VE table (only used when FLASH Update is selected).
  • Update After (events) (AMCupdate_thresh): is the minimum number of AMC RAM VE updates that have to be made before the program will burn the table to FLASH (only used when FLASH Update is selected).
  See the Automatic Mixture Control page for more information.

• Alpha-N Blending: Older MS-II code only allows alpha-N below lo_rpm, a blend between lo_ and hi_rpm, and speed density above hi_rpm. However, the 3.8 code allows you to reverse this so you have speed density at low rpm but alpha-N above hi_rpm. The first setup is for big, "lopey" cams at idle, the second for when MAP peaks to 100 as soon as the throttle is cracked and there is no more load control unless you use alpha-N. There is also added a factor to allow spark advance with baro (when less than 100 kPa) for alpha-N mode. This isn't allowed in speed density since map in the spark table accounts for it. The rate of advance versus baro under 100 kPa is a user input.

• MAP vrs. MAF Usage: The code has MAF (mass air flow) sensor capability and also a combined MAF/ MAP mode. Rather than calculating the air flow from the VE table and manifold pressure (MAP), the mass air flow sensor measure the amount of air directly. In some cases this can make the engine easier to tune, and better at adapting to changing engine parameters. On the other hand, the MAF sensor itself can present an significant airflow restriction to the engine (limiting power), and sometimes can have range limitations if the engine flow a lot more (or less) than the application it was designed for.
  • Enable MAF Use:
  Use this setting to enable exclusive MAF use, or MAP/MAF blending.
  • MAF Hardware Configuration: For MAF only, you hook the MAF to the MAP pin. For MAF/MAP blend, you leave the MAP on the MAP pin, and use either the baro or knock pin for the MAF.
  • MAP Only Above RPM: Use MAP exclusively above the specified RPM.
  • MAF Only Below RPM: Use MAF exclusively below the specified RPM.
  • Invert above MAP/MAF Settings: If yes, then use MAF above the first RPM, and MAP below the second RPM. Normally this should be set to 'use above'.
  With MAF you adjust the MAF Flow vs MAF Correction table to get a decent AFR. So if you have a MAF flow readback of say 15000 mg/sec and the AFR is say 15% lean, then for this flow number you can make MAFCorr = 115% and richen it up to your target. If you need very large corrections, but everything is working, you can put these numbers (original MAF table flow * MAFCorr) in the maffactor table and reset the MAFCorr number to 100% (no correction).

  So if you are connecting a MAF (and not using MAP), disconnect (remove) the MAP sensor, and connect the MAF signal wire to pin#1 of the MAP sensor pad (it is the square one). Ignore the knock and baro pins (or use them for knock or baro, etc.)

  The VE tables are not used when MAF only is selected, because MAF measures the actual mass air flow. The rpm and map arrays for AFR are the same as those for VE because both are fuel related. Also see: www.MicroSquirt.info/mafmap.htm#ms2

• Sampling and Smoothing: The smoothing (aka. "lag") factors force the variables to change more slowly than the actual input value. Note that in all cases, 100 is no lag effect at all, and smaller numbers slow the input response speed. The lag factors are used as follows:
  NewValue = PreviousValue + (NewValue - PreviousValue) * (LagFactor/100%)
  • MAP Averaging Lag Factor
  • RPM Averaging Lag factor
  • TPS Averaging Lag Factor
  • Lambda Averaging Lag Factor
  • CLT/IAT/Battery Averaging Lag Factor
  • Knock Averaging Lag Factor
  • TPSDOT Sample Rate
  • MAP/MAFDOT Min Sample Rate
  • MAP Sample Point Rel. TDCC1
  • MAF Sample Point Rel. TDCC1

  Sampling Rates: Reasonable values for tpsdotSample and mapdotSample are 25 ms for both. If you set mapdotSample and tpsdotSample both to 0, the program will try to sample the TPS input and calculate tpsdot as fast as it can. This will make tpsdot vary all over the place from the tiniest variation in the TPS input. And the same for mapdot. So keep the values reasonable, between ~10 and ~50.

  • MAP Sample Rate: Map and Mapdot are sampled/ calculated every tach pulse. But if you get to too high an rpm, such that the time between tach pulses is < mapdotSample, then it leaves the old mapdot until the next tach pulse. This is done so that the total time is > mapdotSample. This prevents noise fluctuation. It doesn't have any downside because acceleration enrichment becomes less and less important as rpm goes up.
  • TPS Sample Rate: tpsdot is sampled independently with its own tpsdotSample. It is similar to the mapdot however. It is independent of tach pulse arrival and will, if tpsdot exceeds your threshold, add an accel increment to the pulse width when it is time to inject.
  • MAP/MAFDOT Min Sample Rate: This is the minimum rate (in milliseconds) at which to calculate the MAFdot or MAPdot values.
  • MAP Sample Point Rel. TDCC1: This is the point in the engine cycle at which to sample the manifold air pressure (relative to top dead center on the compression stroke for cylinder #1).
  • MAF Sample Point Rel. TDCC1: This is the point in the engine cycle at which to sample the mass air flow (relative to top dead center on the compression stroke for cylinder #1).

• Max. Cranking Speed: This is the engine RPM below which the cranking pulse widths will be used (at one injection per ignition event), and the MAP and IAT, VE table, EGO feedback, etc. will be ignored. The cranking speed setting should be above your actual cranking speed by at least 50 to 100 rpm. Otherwise you are never in cranking mode. So the cranking speed should be set somewhere between your actual cranking speed and the idle speed (most engines crank between 160 and 250 rpm, so typically the cranking speed will be set to 300 to 350 rpm).
• TPS for Flood Clear Mode: This is the minimum throttle position sensor value that will trigger flood clear mode, in which no fuel is injected while cranking (to clear excess fuel from the intake manifold and cylinders).
• VE/SPK/AFR table index: The normal option is to make the VE table a function of MAP and RPM, the other is to make VE a function of MAP/baro and RPM. To keep everything compatible, the code uses (MAP/ BARO) * 100 kPa, so if you are at standard barometric pressure, there is no difference. This is meant to be used with an independent baro sensor and with no other barometric correction, although you have to set the baro correction parameters so that the correction comes out that way. The idea is that volumetric efficiency is not only a function of the pressure on the intake, but also of the exhaust back pressure. The thermodynamic engine efficiency equations come out as a function of MAP/baro, so this is offered as an option. When you are not at standard pressure, it will shift your VE table so it may appear that it is screwing everything up, but if you are willing to re-tune your VEs with this option, doing it at sea level, then you should be able to climb a mountain with no baro correction. It won't result in a big improvement over what we used before, which is a 10 point correction table that you can tune to give you a very precise correction, but it is the thermodynamically correct way to do it. This is an advanced option for people who want to experiment and have some understanding of engine thermodynamics. Someone just starting to use MegaSquirt^® doesn't need to use this. Note that when changing this setting, in addition to changing this setting in TunerStudioMS, you must change the project properties settings to enable MAPbaro:

  otherwise the tables will not show on the menu (they will be grayed out).

• Res Gas Model VE Calc: There are four Residual Gas Model options here:
  1. Use VE table only, do not use the residual gas model at all.
  2. Use the residual gas model to calculate VE. This only applies to MAP-only or MAP/MAF blend and is for display only, it is not used to influence the pulse width;
  3. same as 1, but use VERGM calculation for the VE term in the airflow/fueling calculation;
  4. same as 2, but also multiply the RGM VE by the table VE to fine tune the fueling.
• Valve Overlap Factor: This is from Fox and Heywood's Residual Gas Model. It is used to calculate VE from MAP sensor readings. Typical values for the valve overlap factor are 0.5 to 1.5 deg/m.
• RGM Coeff 1 (Backflow): Coefficient for the backflow term of the Residual Gas Model. This, and the trapped exhaust gas recirculation coefficient below, can be used for tuning the RGM model.
• RGM Coeff 1 (Trapped egr): Coefficient for the trapped exhaust gas recirculation term of the Residual Gas Model. This, and the backflow coefficient above, can be used for tuning the RGM model.
• AFR Table Fuel Calc Usage: The default (Use Combined AFR/VE table) calculates the fueling based on the VE table (and MAP, IAT, etc.). The AFR table in that case is used ONLY for EGO feedback control. However, by selecting the 'Separate AFR/VE table', you can have the fuel equation multiplied by the AFR table entry divided by the stoichiometric AFR, meaning the AFR is always in the calculations. In the default case, AFR and VE are really combined into the VE table, while in the other cases they are separate. Either will allow you to control a wideband EGO sensor, but the difference is that while the first relies on EGO feedback to reach the target AFR in the AFR table, the 'Separate' options do not relay on the wideband feedback, instead the target AFR are fed directly into the fuelling equation. With the separate tables, IF the VE table is correct, then changing the AFR table to another target should result in that AFR, even without EGO feedback control.

  MegaSquirt historically always includes the AFR in the calculation as part of the VE table, unless you have 2.8+ MS-II code, and have set the 'Use separate VE & AFR table' option under 'Fuel Set-Up/Other Fuel Settings'

  The reason the AFR and VE tables were combined in the early codes is that they are tuned together. That is, you tune the VE table to get the AFR you want. So in practical terms, there was nothing to be gained by separating them, they would do the same thing (and eat up more memory). This was before wide band sensor were widely available.

  When wide band sensors became popular and relatively cheap, the AFR table was invented to set targets for the wide band sensor, and nothing else. So it affected fuelling 'after the fact' in the ego correction, but was NOT used in the initial fuel pulse width calculation. In this case, setting the VE to the 'true VE' would result in ego correction trying to reach the AFR target. But if you wanted EGO correction to be minimal, you would still put VE*AFR in the VE table.

  However, it was realized that there was some educational value in separating out the AFR and VE tables, since these are both real physical quantities, and it helps to understand how the engine is working if both quantities appear in the fuelling equation. So using 'separate VE & AFR table' takes the AFR table from an EGO correction to act as both ego correction AND a part of the initial fuel calculation. In this case, the 'true VE' would go in the VE table, the desired AFR goes in the AFR table, and the EGO correction should be minimal (assuming everything else is correct, of course).

• AFR Stoich. Ratio (Volts/AFR): This is the stoichiometric ratio (or voltage) used with your fuel and a wideband EGO controller (or narrow band if volts). For a wideband installation, it is used for calculating the fuelling with separate table. For a narrow band, it is used to set the 'EGO switch point' to the only value at which a narrow band has meaning: stoichiometric (chemically correct).
• AFR Stoich. Ratio: This is the stoichiometric ratio (or voltage) used with your fuel and a wideband EGO controller (or narrow band if volts). For a wideband installation, it is used for calculating the fuelling with separate table. For a narrow band, it is used to set the 'EGO switch point' to the only value at which a narrow band has meaning: stoichiometric (chemically correct). Two-Point Prime:
• Prime Pulse Cold PW: If you are using 2-point prime (rather than a table), this is the prime pulse at the highest temperature in your temperature table, values for the prime pulse will be linearly interpolated between this and the cold prime value depending on the coolant temp at cranking.

• Prime Pulse Hot PW: If you are using 2-point prime (rather than a table), this is the prime pulse at the highest temperature in your temperature table, values for the prime pulse will be linearly interpolated between this and the cold prime value depending on the coolant temp at cranking.

The prime pulse is NOT meant to provide starting fuel (it is meant to clear any air that might have leaked into the fuel system while the engine was shut down), that's what the cranking pulses (see below) are for (as they are both rpm and temperature dependent, and thus much more likely to give the correct amount of fuel for starting under all conditions).

The actual pulse width is determined by performing linear interpolation on the line described by the end points you enter for the 'hot' and 'cold' values. For instance, if you enter 10.0 milliseconds as the pulse width at -40°F and 2.0 ms at 170°F, the pulse width will be 6.0 ms when you start your engine at 65°F.

• Prime Delay: This is the time, in seconds, after controller start-up when the fuel prime pulse (if any) begins. This allows for the fuel pump to reach full pressure for the priming process.

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• Base Ignition Settings:
  • Trigger Offset (deg) (adv_offset in the code) is the advance before (or after) top dead center (BTDC) that the engine gets in it's signal from the engine's variable reluctor (VR) or Hall sensor. In many cases, this will be used as the 'base timing' for cranking as well as if the module loses its connection the ECU.

  • Skip Pulses (no_skip_pulses) is the number of ignition pulses at start-up that MegaSquirt-II uses to calculate the rpm before sending calculated advance signals.

  • Predictor Algorithm is the scheme used to anticipate the amount of time before the next TDC event (to properly schedule the fuel and spark events). It can be either last interval or alpha-beta-gamma filtering:
    • Last Interval: This simply uses the last interval between tach pulse as the 'best estimate' for the next interval ,
    • Alpha-Beta-Gamma Filtering: The alpha value (aka. "alpha gain") is like the proportional value in the ego loop, the beta is equivalent to 1st derivative weighting and gamma to 2nd derivative. The defaults are the best place to start.
      • alpha (α) should be > 50% and < 150%; (default is 90%). The value of alpha will be typically be 90 to 100% or a bit higher.
      • beta (β) should be < 100%, (default is 80%) The value of beta will be moderately small so that speed estimates are not unduly affected by variations from input data. A typical value is around 5% to 80%, and
      • gamma (γ) should be < 50% (default is 10%). The gamma gain term helps to track changes with less sensitivity to input data and helps to maintain consistency between the velocity and acceleration variables. A typical value is around 10%.
      Setting alpha = 100 and beta, gamma both to 0 gives the 'Last interval' prediction. The alpha-beta-gamma filter doesn't show that a great improvement over the previous schemes but they are always much better than 'Last Interval'. They are much more efficient to compute as well (about 20 µsec CPU) and save many lines of code. For more on alpha-beta-gamma filtering, see: www.megamanual.com/ms2/alphabeta.htm

  • Tach Signal Masking: In the code are two input variables to control the interrupt masking to prevent false triggers. They are primarily there to mask the false triggering from coil ringing when triggering off the coil negative terminal. These are changed in the 'Ignition Set-Up/Base Ignition Settings' dialog of TunerStudioMS:
    1. Time Mask time (milliseconds) after tach input capture during which further interrupts are inhibited to mask coil ring or VR noise, and
    2. Percentage Mask is the percentage of the predicted interval before the next tooth (dtpred) after the last tach input capture during which further interrupts are inhibited to mask coil ring or VR sensor noise.

    Because the coil ringing is mostly a function of time (not the interval between firings), the time mask is usually most effective in preventing false triggering (and the resultant tach spikes) when firing off the coil's negative terminal if the dwell is constant. However, the dwell is always constant (because of cranking, or because the engine is running fast enough that there isn't enough time for full dwell), so the percentage mask can be helpful as well.

    Note that unlike the next pulse tolerances below, the masking is designed to prevent false triggering that would create additional tach events that were false. The next pulse tolerances are designed to 'catch' errors and adjust the tach/tooth count (or reset the ignition) when an error occurs.

    For wheel decoding an M-N crank wheel you must use values close to 0.2 ms and 10%. However, to not break any existing setups, the default values are 0 and 50%, the same values that are 'hardwired' into pre-v2.5 code. Be sure to adjust these values when you set up for a trigger wheel (note that they are in a separate dialog from the trigger wheel settings).

  • Next Pulse Tolerance (%) (PulseTol) is the tolerance during which the next pulse is not allowed to count as a 'true' pulse, and is counted as a false trigger. These allow the code to have some way of knowing that the tach pulses are not arriving in a manner consistent with the configuration. The tolerance is a check on the percentage change in times between tach pulses, or between teeth if using an M-N missing-tooth wheel.

    The next pulse tolerances are designed to 'catch' errors and adjust the tach/tooth count (or reset the ignition) when an error occurs. Note that unlike the next pulse tolerances, the time and percentage masking above is designed to prevent false triggering that would create additional tach events that were false.

    So if the time between the last two events is X, then if then next pulse occurs within X-PulseTol, it is rejected as a false trigger. If a pulse is NOT received after X+PulseTol, a tooth is assumed to have been missed. This only occurs after the first few pulses (as specified in the Skip Pulses). In later versions of the MS-II code, the next pulse tolerance can be set under three different conditions:

    • Cranking: This is the next pulse tolerance while cranking (enginebit=3) - it should be set fairly high. This is because the starter motor speed can vary quite a bit, depending on the compression and which cylinders happen to reach firing conditions first, etc.
    • After-start: This is the next pulse tolerance while afterstart enrichment is active, and in general it should be lower than the value while cranking if you find you have to tune this to get a clean tach signal (even though the default after-start value may be higher than the default cranking value).
    • Normal Running: This is the next pulse tolerance once afterstart enrichment ends, and it should be the lowest of the three (since the engine speed is more stable in normal running conditions - there's more rotational inertia, and fewer variations in things like air/fuel mixtures. As well, if you have a VR sensor, the signal is stronger, etc.)
    In all cases, adjust the above numbers to get the cleanest signal while cranking, during after-start or during normal running. You might have to ignore the advice to adjust them so that normal running is lower than after-start, which in turn should be lower than cranking. Instead, do what works best for your installation.

  • Check Tach Sync Options:

  • Ignition Input Capture (ICIgnOption Bits 0-3) - changes requires an MS-II reboot - This is the ignition input signal event that should signal the base timing (Advance Offset) has been achieved. For example, the GM 7-pin HEI module takes the variable reluctor signal, and generates a positive going pulse when the base advance point is reached. In this case, the 'Rising Edge' is chosen, as the positive going transition is used as a trigger.
  • Cranking Trigger - changes requires an MS-II reboot This can be 'calculated', in the normal manner, or you can have the spark occur when the 'trigger return's, i.e. goes low. Trigger return essentially uses the module's base setting for cranking timing.
  • Coil Charging Scheme (ICIgnOption Bits 4-7) - changes requires an MS-II reboot - This is used to specify whether the spark occurs on the falling edge of the output signal ('Standard Coil Charge' such as HEI) or the spark timing is generated by the ignition module (EDIS, etc.) In a standard system, the coil 'sparks' when the current to the coil is interrupted. This is the 'Standard Coil Charging' option and is used with the GM 7-pin HEI module, for example. With the EDIS system, and others, though, it is the length of the pulse that determines the timing, not the actual timing of the pulse, so you would select the EDIS option.
  • Spark Output (spkout_hi_lo) - changes requires an MS-II reboot You can choose between spark when going low (ground) or spark when going high. However, note that the terminology was developed for the original MS-II (non-CAN) units, which had an additional transistor in the ignition output path. This transistor inverted the signal. The result is that with later, CAN-enabled MS-II's, in which the extra ignition transistor was removed to make room for the CAN chip, you need to select the opposite of the described output. I.e. select going low (normal) if you want to spark when the processor output goes high, and vice versa. For example, if you are using the VB921 (or BIP373) to control a coil directly, you would select 'going high(inverted)'. The terminology will be corrected in the V3.0 code.
  In general, use the default options and values unless you have a reason to do otherwise.

• Dwell Settings:
  • Maximum Dwell Duration (ms) (max_coil_dur) is the longest period the coil is allowed to charge - too long and it can burn out your coil, too short and the spark may be weak. Normally this value is between 2.0 and 4.0 milliseconds.
  • Maximum Spark Duration (ms) (max_spk_dur) is the amount of time MegaSquirt-II tries to wait before starting another charging cycle.
  • Acceleration Compensation (ms) is the amount of time added to the duration when the accel enrichment is activated.
  • Battery Voltage Compensation (deltV_table & deltDur_table) is the time added to the dwell to compensate for low battery voltage. You can select both the trigger bin levels (V) as well as the duration added to the dwell (ms). You set the Voltages as 'offsets' from twelve volts. For example, a Voltage 3 (V) setting of 0.0 means the durations compensation applied at 12 volts. As another example:

    Bin	Voltage (V)	Duration (ms)	Comment
    1	-4.0	2.0	Increases dwell by 2.0 milliseconds at 8.0 Volts
    2	-2.0	0.9	Increases dwell by 0.9 milliseconds at 10.0 Volts
    3	0.0	0.0	No compensation is applied at 12.0 volts
    4	2.0	-0.5	Decreases dwell by 0.5 milliseconds at 14.0 Volts
    5	4.0	-0.9	Decreases dwell by 0.9 milliseconds at 16.0 Volts

    In general, you should have small positive numbers in the negative bins, and small negative numbers in the positive bins. DO NOT rearrange the order of the voltage bins.

    The -4.0 and -2.0 bins are useful for generating a good 'hot' spark for cranking. Note that normal running voltage is often about 14 volts, which in this case would remove 0.5 milliseconds. Be very careful not to put overly large numbers in these bins. You engine may now run at all or may run poorly with large negative numbers, and may burn out the coil with large positive numbers.

• Advanced Ignition Options: MegaSquirt-II code (V2.6+) can be configured to use a missing tooth crank wheel for the tach input. The wheel must be of the form M-N, where M>N, and there is only one set of continuous missing teeth. Common OEM wheels are 36-1 (used with Ford's EDIS and others) and 60-2 (common on many makes).

  Note that you should change these parameters only with the engine OFF (or the stim rpm at no more than 300 rpm).

  The missing tooth code uses the teeth of the missing tooth crank wheel to create 'tach teeth'. That is, it creates a tach signal from a particular tooth, then skips a number of teeth before declaring another tooth a tach signal. This means that all the tach teeth must correspond to real teeth. For a four stroke cycle engine, this means that the total number of teeth, including missing ones, must be evenly divisible by ½ the number of cylinders (or by the number of cylinders for a 2-stroke).

  There is more information on the trigger wheel usage in the missing tooth trigger wheel decoder page.

  The trigger wheel settings are:

  • Trigger Wheel Teeth (No_Teeth): is the nominal (include missing) teeth for wheel decoding. (0=no wheel decoding).

  • Missing Teeth (No_Miss_Teeth): Number of consecutive missing teeth.

  • Skip Teeth (No_Skip_Teeth): Number of teeth (between tach pulses) to be skipped. You must create the same number of 'tach' signals as you want ignition events. On a four cylinder four stroke engine, this is two per revolution. Suppose it has a 60-2 wheel. What you need to have happen is for MegaSquirt-II to 'skip' a certain number of teeth so the only the right number of teeth are counted as 'tach signals' per revolution. Since we have determined the number of tach signals we want is 2, we need to skip 60/2 = 30 teeth. For a eight cylinder 60-2, we need 4 ignition events per revolution, so we set skip teeth to 60/4 = 15. And for an eight cylinder 36-1 wheel, we would set skip teeth = 36/4 = 9.
  • Delay Teeth (Delay_Teeth): Number of teeth to delay after 1st tooth after the missing teeth before 1st tach synch declared. You get synch as soon as you detect "first real tooth after the missing tooth". If that tooth is at TDC when it is detected, then there is 0 delay. If TDC doesn't occur until the next tooth is detected, then there is a delay of one tooth, and so forth.
  • Dual Spark Options:
    • No Dual Spark

    • Dual Tach Inputs for 2 ignition inputs and 2 outputs. Specifying this option uses the 2 pwm1,2 pins (TC2,TC4) for the extra ignition in, out; therefore there is NO injector PWM with this option. Also, NO trigger return, NO wheel decode, and NO EDIS. Also set ISR_tmask=0,_pmask < 20. The inputs are from 2 or 4 cyl crank or 4 cyl cam. They are independent, allowing 2 cyl, possibly 4 cyl odd fire.

    • Falling Cam Sync with Tach or Wheel,or Rising Cam Sync with Tach or Wheel for 2 cyl COP/ 4 cyl wasted spark with normal tach pulse or M-N or M-0 wheel on input 1, cam synch on input 2; option 2= falling, 3= rising edge for cam synch. When cam synch occurs, fire Output 1, then fire O/P 2 on next tach, etc. No injector PWM, NO trigger return, and No EDIS. On MicroSquirt^® EFI controller, cam_sync must fall inside missing tooth gap; with the MS-II Sequencer™ controller board cam_sync can come anywhere after Cam_Tooth and before 1st tooth after missing gap.

    • Single Crank Wheel Input is same as 2 and 3, but with 1 toothed wheel on input 1 (input 2 is unused). On tooth after missing tooth(teeth) fire output 1, then fire output 2 after skip teeth (= next tach), etc.

    • Single Cam Wheel Input same as 4 except wheel on cam, so use 1/2 crank skip teeth.

    • Dual Inputs, Timing from 1 cam tooth same as 1 except timing signal from 1 cam tooth, 2 cyl only.

    • N-0 Wheel w/ Falling Crank Sync or N-0 Wheel w/ Rising Crank Sync same as 2,3 but crank synch on 2nd input, no missing teeth. These options can support odd-fire through the OddAng input. These are meant for crank wheels, generally flywheels, with no missing teeth and a nub or bolt or hole in the flywheel that is sensed by a separate VR sensor. It is a wasted spark mode, not a sequential. Also, even if a mode says M - 0, you still have to put the missing tooth in as 0.

  • Offset (advance) for Output #2: With the Dual Spark function enabled, the trigger offset should be set 'negative'. That is, there are always two choices for trigger offset. The timing looks as follows:

     
          ...----|<------ degrees between firings -------------->|----...             
          ...----|--------------|--------------------------------|----...                      
          ...- tach1-----------TDC-----------------------------tach2 -... 
          ...----|<--(+)x deg-->|<------(-)y deg---------------->|----... 
    

    So in theory you can normally pick either +x° (BTDC) or -y° ATDC (where x° + y° = degrees between firings = 90° for a 8 cylinder, 180° for a 4 cylinder, etc.).

    For non-Dual Spark function, it doesn't matter which offset you choose because the dwell + spark sequence for a cylinder can be anywhere in the cycle, and we have generally used positive (+) degrees in the documents. But for Dual Spark, because it is too complicated and there is not enough RAM or CPU time, you must start and finish both dwell and spark within the time between 2 consecutive tach pulses. In this case we always want to use the negative y degrees, or else the math ends up coming out incorrect in the code.

    For example, if tach1 occurs at a trigger offset of +40° BTDC, tach2 occurs -320° ATDC (and there is 360 degrees between firing, so a 2 cylinder engine). For dual spark mode we always want a negative trigger offset, so you would use -320° instead of +40°.

    The -320° offset seems unusual, but there is a reason for it. The original code started with a very robust triggering system where people could put their sensors anywhere and use any kind of advance with any kind of offset. This was a nightmare to code and impossible to maintain with the dual spark system, which was based on a strictly next cylinder firing setup. In fact it sets up to fire 2 cylinders before the actual spark occurs. This allows plenty of time for dwell at high rpm. To maintain the previous terminology for users as well as keeping the code consistent, the advance offset was left as it was, but whereas for the original (non-dual spark) system it was best to use a positive trig offset (but negative offsets would also work), while dual spark requires a 0° to negative (ATDC) advance offset.

    If you try to put in -320° offset in some older TunerStudioMS ini files, it won't allow it, so use the latest 3.8 ini file which opens up the limits to +/359°.

    For more info on the Dual Spark options, see this page: www.MicroSquirt.info/dualspark.htm

  • IAT-based Spark Retard Limiting Options:
    • Start IAT Retard: RPM at which to begin applying the intake air temperature based spark retard amount. It will be zero below this, and rise linearly to the full amount at the Full IAT Retard rpm (below).
    • Full IAT Retard: RPM at which to fully apply the intake air temperature based spark retard amount. It will be the full amount of retard above this, and fall linearly zero at the Start IAT Retard rpm (above).
  • Signal Delay Parameters:
    • FET Output Delay: This setting is intended to adjust for the slight delay between when the processor sends the output signal to the FET (output transistor) and when the transistor actually turns on. The delay is very small, but measurable, and useful mostly in laboratory conditions where highly accurate measurements can be obtained. For users in the real world, there is no need to change this from the default value.
    • VR Input Delay: For those lucky enough to know the latency (delay time) between the physical event the VR sensor is capturing and the time the signal is generated. This has an effect on timing because it does not change with rpm, so it is a constant added to the variable time difference between teeth. It is useful for doing very precise timing of specific events. In the real world, very few can measure this latency, and even fewer would see any improvements by adjusting it (you would have to calibrate everything else in the system). It is primarily useful for those working in a laboratory.

  Return to help index

• Knock Threshold:
  • File
    • Fetch from ECU: Get the current knock settings from MegaSquirt.
    • Burn to ECU: Send the currently displayed knock settings to MegaSquirt.
    • Exit: Leave the knock sensor setting dialog.
  • Settings -> Knock Sensor Settings
    • Knock Control knk_option:
      • Disabled: do not use knock feedback for ignition advance control.
      • Safe Mode: use knock retard, but keep the advance below that which caused knock.
      • Aggressive Mode: use knock retard, but keep advance at threshold of knock occurring.
    • Threshold Direction: This sets whether MegaSquirt^® recognizes a voltage above the threshold (see next item) or below the threshold is considered knock.
    • knock value at 0V (V) knk-thresh: The is the voltage from the knock sensor module which defines whether there is knock occurring or not. Note that you can define a 6-element table of rpm versus voltage instead of a single value. You define this table under 'Settings/Knock Threshold'.
    • knock value at 5V knockmax: the maximum expected voltage value on the knock signal, used in some configurations where the difference between the signal level and the maximum levels indicates the degree of knocking.
    • Knock Count (knocks) knk_nde: number knock detects required for valid detection
    • No Knock Above MAP (kPa) knk_maxmap: no knock retard is implemented above this MAP
    • No Knock Below RPM (rpm) knk_lorpm: no knock retard is implemented below this rpm
    • No Knock Above RPM (rpm) knk_hirpm: no knock retard is implemented above this rpm
    • Maximum Retard (deg) knk_maxrtd: maximum total retard when knock occurs
    • Retard Check Time (sec) knk_trtd: this is the time between knock retard corrections, allows short time step to quickly retard
    • Retard Step Size (deg) knk_step1: ignition retard step size when 1st knock or after stopped, make it large to quickly retard the timing and stop knock
    • Advance Check Time (sec) knk_tadv: this is the time between knock advance correction (I.e., timing return to 'normal')
    • Advance Step Size (deg) knk_step2: ignition advance steps after knock has stopped
    • Recovery Advance (deg) knk_dtble_adv: this is the change in table advance required to restart advance until knock or reach table value (0 knock retard) process. This only applies in 'Safe Mode'
  • Tools
    • Curve Generate:
  See the knock sensing system page for more information.

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• VE Table X (MAP or MAP/baro)

  All interpolation in MegaSquirt^® uses table end points (NOT extrapolation) when the indexing value exceeds the limits of the table, but that fact is especially important when considering the computations of volumetric efficiency from the VE table. This means that if your biggest MAP bin contains 100%, then any MAP value over this will produce 100% (for a given RPM). This does NOT mean that the pulse width will be the same for MAP readings of 100 kPa and 200 kPa, the MAP value is used to scale the pulse width accordingly, so for this example you will get twice as much fuel.

  To clarify how all these factors are used, the basic pulse width calculation (containing no enrichments, etc.) is.

  PW = nominalPW * airDensity * VE
  In TunerStudioMS, the nominal pulse width is called Required Fuel. This number gives a value (in milliseconds) that provides exactly the correct amount of fuel for stoichiometric combustion when the temperature is 70 F, the atmospheric pressure is 100 kPa and the engine is operating at 100% volumetric efficiency. Air density is calculated from MAP and air temperature.

  Volumetric efficiency is a function of many factors (intake and exhaust tract design, camshaft lobe shape, and so on) but can be characterized very well for a given engine by MAP and RPM. I could go on about resonance and laminar flow, but it is sufficient to say that at low MAP (30 kPa), the VE is typically very poor due to turbulence effects, so VE is low (maybe 10-30%). At the MAP values 100 kPa and higher, the torque curve is a close reflection of the VE curve, so expect the VE values to peak at about the same point.

  Very Important Note The VE values in MS do not reflect the true VE in your engine, since you usually do not want to run stoichiometric combustion in all operating regimes! They are a combined value giving the VE multiplied by any enrichments or enleanments that you desire. When your turbo motor is running at 250 kPa and has a true VE of 100% at 14.7:1 AFR, you would enter 111% to get 13.2:1 AFR.

• VE Table Entries

  The Required Fuel value determines the ideal pulse width at 100% VE. The entries in this table scale that value to determine the actual pulse width (neglecting all correction factors and enrichments). As such, both the required fuel and the VE table entries are more or less arbitrary, but it is useful to make them as close to correct as possible. In other words, if your required fuel value is 15.0 ms and the VE table entry being used is 100%, you could achieve the same pulse width with 10.0 ms and 150%, respectively. It is also important to understand that these VE values do not indicate the amount of fuel delivered over time. For example, if you have a row in the table that is 100% across the board, then fuel delivered is proportional to RPM. Say that the engine is running at 2500 RPM and the pulse width is 12.0 ms. If you speed the engine up to 5000 RPM the pulse width will remain at 12.0 ms, but this delivers twice as much fuel because there will be twice as many injection events in a given time interval.

• MAP Bins

  The MAP bins define the range over which you can vary the VE values used for pulse width calculations. These values are in kPa (absolute) and can vary from 0 to 255 kPa; usually 0 to 100 for a naturally aspirated motor and 0 to max boost on a turbo- or supercharged one. The biggest value might be 100%, even for a turbo motor, IF you want the fuel at boost to be linearly proportional to MAP. Typically, though, you want some values above the 100 kPa value to add fuel as coolant when boosting. This might result in a table that looks like this: MAP VE (%) ... 100 80 150 100 200 100 250 120 4000 RPM to ensure that extra fuel is delivered when boost is applied. The low MAP bin value should be around 20 kPa for a stock type engine and the top value should be around the maximum pressure that you expect your engine to see (100 kPa for naturally aspirated engines, somewhat over max boost on a turbo- or supercharged motor to give yourself some headroom). The MAP bin values are stored in MegaSquirt^® as "KPARANGEVE."

• RPM Bins

  The RPM bins define the range over which you can adjust VE based on engine speed. If you have a representative torque curve for a motor like yours (ideally from a dyno run, but probably nearly as good from one of the many engine simulation packages available), you can set the spacing of these values from that. Find the places on the graph where the curve is "bending" the fastest (i.e., has big second derivatives; usually from idle to up near the torque peak) and use smaller RPM intervals over these. For long stretches where the curve is straight, but not necessarily horizontal, you can use bigger gaps in the bins. The reason for this is that the algorithm is going to do linear interpolation between these points (that is, it is going to play connect-the-dots), so you will have smaller error between bin points if you choose them well. It is usual to have the low end of the torque curve well represented, down to idle, and the top end should be somewhere near your redline value. For a street engine, the torque curve is usually dropping rapidly at redline, dictating that you have that top value up near redline. On a race motor, you are much nearer the torque peak, so will probably group the RPM bin values more tightly up there for finer control over the range of interest. The RPM bin values are stored in your MegaSquirt^® controller as "RPMRANGEVE".

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  • File
    • Table Export you can export or import VEX files into any of the VE, AFR or ignition tables. Use the 'Table/XXX Table/Files/VE Table Export' dialog to export them. These are all saved in the VEX format, so be sure to give your saved files descriptive names.
    • Table Import you can export or import VEX files into any of the VE, AFR or ignition tables. Use the 'Table/XXX Table/Files/VE Table Import' to import them. These are all saved in the VEX format, so be sure to give your saved files descriptive names. The table will import VEX files of different sizes and automatically adjust them to match the current table size.
    • Exit - leave the table editing dialog.
  • Tool
    • Contour gives you a 'contour plot' of your table, showing visually how smooth it is by varying the color depending on the table entries. Because MegaSquirt^® interpolates between the bin values on the tables, the contour plot gives a realistic view of how the table will be used . 
    • Table Transform gives you the ability to: 
      - 'Scale' the whole table by a factor (1.0 results in the same table, 2.0 doubles all the values),
      or
      - 'Shift' the whole table by the specified number of VE% units, for example, entering 2.0 adds 2% to each VE table entry.
    • VE Specific
      • Reset ReqFuel allows you to 'rescale' the VE table so that your you req_fuel will combine with the computed VE table to produce the same injector pulse widths at any given rpm and kPa. It is especially useful when changing injectors or fuel pressure.
        
      • Generate Table This is a tool for establishing a baseline VE table for your tuning efforts with MegaSquirt^® EFI Controller, MegaSquirt-II and UltraMegaSquirt. The VE curve is assumed to follow the torque curve (which is not quite right, but close enough for a first approximation). This calculator is based on modeling your engine's wide-open-throttle VE with a quadratic equation of the form:
        VE = A*RPM² + B*RPM + C
        
        where A, B, & C are constants.

        These constants are derived from the:

        • Peak torque@RPM,
        • Peak horsepower@RPM,
        • The assumption that the peak torque occurs at the VE curve's maximum (i.e., the first derivative with respect to RPM is zero).
          
        An assumption has been made about the VE required to produced 1 lb·ft/ci as well as 1 hp/ci. A further assumption has been made that compressor efficiency=60% for kPa>100. Finally, a scaling factor has been used to adjust the wide-open throttle VE for lower MAP values. The factor is derived from examples of working VE tables. A limit of 5% per RPM bin drop in VE has been applied to prevent the extreme drop-offs that can occur at high RPM & kPa when VE is modeled in this way. As well, all VEs are restricted to be not less than 25% of the highest VE, to prevent unusable idle values. This calculator has not been tested on all possible engine combinations and operating parameters. Use it at your own risk.
        WARNING! WARNING! WARNING!
        The VE tables generated are only estimates, sometimes very poor estimates, and unthinking use of the table can destroy your engine! You must tune your engine after generating the VE table, especially up in the high load parts of the table, to make sure your engine has sufficient fuel that it does not detonate or go lean and burn some pistons. Every effort was made to assure that this generator produces rich conditions, but that is not guaranteed. Note also that it generates a VE table for speed-density mode, not for alpha-N mode.

        1. Inputs Fill in all of the values (use your best estimate if you don't have measured numbers, but remember your table will only be as good as your estimates, and sometimes quite a bit worse).

        • Engine Displacement The total swept displacement of your engine (more precisely, the air that your engine would pump in a single cycle at 100% VE). Nothing tricky here, just tell TunerStudioMS how big your engine is.
        • Idle Characteristics These values define the lower left corner of the VE table, so put in the values that you want as the lower bound for both RPM and MAP.
        • Peak Torque Enter your best estimate for peak torque in lb-ft in the "Value" field, the RPM and expected MAP for that torque peak. Now if you are dealing with a naturally aspirated engine, use 100 kPa for the MAP, but if you super- or turbocharging and have good numbers for a similar motor use the torque, RPM and boost at which that torque was produced, irrespective of your intended actual boost pressure.
        • Peak HP Enter you best estimate for peak crankshaft HP and the RPM and MAP corresponding to that HP. Again, if you have a boosted application, use the HP, RPM and MAP corresponding to on another.
        • Redline Characteristics Enter the RPM and MAP values you want to see in the upper right corner of the VE table. If these values are different (either higher or lower) the table will still be interpolated over the range defined by the Idle and Redline ranges.
          
        2. Generate The Table
        When you click "Ok", the table is generated and sent down to the MegaSquirt^® controller.

        3. Verify
        

        • Pop up the VE table, Settings->VE Table, and verify that the VE numbers and MAP/RPM bins look reasonable for your engine.
        • Remember that the table generated is only a starting point for tuning. Using the generated table as a 'final' table under severe operating conditions can destroy your engine. Be sure to follow the tuning guide, and get professional assistance whenever you are not sure.

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• AFR Table X (afr_table) (wide band EGO option only) 
  If you have a wide band sensor, fill in the air/fuel ratio table. Generally, you want it to be lean in the areas where it is lightly loaded and you want best economy. You may be able to run as lean as 17:1 in these areas. At WOT, conventional wisdom is that you want 13.0:1 at peak torque, and 12.5:1 at peak horsepower. Then blend the WOT and economy areas so that there is a smooth transition. You will have to do this twice if you have selected the dual table option above.

  Note that you can export or import VEX files into any of these tables. Use the 'Table/XXX Table/Files/VE Table Import' to import them, 'Table/XXX Table/Files/VE Table Export' to export them. These are all saved in the VEX format, so be sure to give your saved files descriptive names. The table will import VEX files of different sizes and automatically adjust them to match the current table size.

  • File
    Note that you can export or import VEX files into any of these tables. Use the 'Table/XXX Table/Files/VE Table Import' to import them, 'Table/XXX Table/Files/VE Table Export' to export them. These are all saved in the VEX format, so be sure to give your saved files descriptive names. The table will import VEX files of different sizes and automatically adjust them to match the current table size.
    • Table Export you can export or import VEX files into any of the VE, AFR or ignition tables. Use the 'Table/XXX Table/Files/VE Table Import' to import them, 'Table/XXX Table/Files/VE Table Export' to export them. These are all saved in the VEX format, so be sure to give your saved files descriptive names. The table will import VEX files of different sizes and automatically adjust them to match the current table size.
    • Table Import you can export or import VEX files into any of the VE, AFR or ignition tables. Use the 'Table/XXX Table/Files/VE Table Import' to import them. The table will import VEX files of different sizes and automatically adjust them to match the current table size.
    • Exit - leave the VE table editing dialog.
  • Tool
    • Contour gives you a 'contour plot' of your table, showing visually how smooth it is by varying the color depending on the table entries. Because MegaSquirt^® interpolates between the bin values on the tables, the contour plot gives a realistic view of how the table will be used .
    • Table Transform
    • VE Specific - not used for AFR table, used for VE tables only.
      • Reset ReqFuel
      • Generate Table

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• Spark Advance Table

  This is the total spark advance (before top dead center) you want at a given rpm and MAP. That is, it includes the effect of the trigger offset. IAT, cold advance, and other adjustments are made to these table values. The values are interpolated between cells. For info on how to set up the advance table, see: www.megamanual.com/begintuning.htm#advance and www.megamanual.com/ms2/tune.htm#spark

  • File
    • Table Export you can export or import VEX files into any of the VE, AFR or ignition tables. Use the 'Table/XXX Table/Files/VE Table Export' dialog to export them. These are all saved in the VEX format, so be sure to give your saved files descriptive names.
    • Table Import you can export or import VEX files into any of the VE, AFR or ignition tables. Use the 'Table/XXX Table/Files/VE Table Import' to import them. These are all saved in the VEX format, so be sure to give your saved files descriptive names. The table will import VEX files of different sizes and automatically adjust them to match the current table size.
    • Exit - leave the table editing dialog.
  • Tool
    • Contour gives you a 'contour plot' of your table, showing visually how smooth it is by varying the color depending on the table entries. Because MegaSquirt^® interpolates between the bin values on the tables, the contour plot gives a realistic view of how the table will be used .
    • Table Transform gives you the ability to: 
      - 'Scale' the whole table by a factor (1.0 results in the same table, 2.0 doubles all the values),
      or
      - 'Shift' the whole table by the specified number of AFR units, for example, entering 2.0 adds 2.0° to each ignition advance table entry.
    • VE Specific - not used for ignition table, used for VE tables only.
      • Reset ReqFuel
      • Generate Table

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• Temperature Table Values: This lets you adjust the values used for all temperature related tables. For example, you can raise the maximum temperature to 180°F or 200°F or even more. Or, if it doesn't get cold where you live, you can raise the minimum temperature from -40°F, etc.

• Alpha-N MAP Table: With Alpha-N (set it under 'Fuel Set-up/Injector Control'), you fill in a 6x6 table ('Other Tables/Alpha_N MAP table') that defines how the TPS is translated into a 'faked' MAP kPa that is then used with the 12x12 VE table.

  So the ECU uses the TPS to look up the MAP in the 6x6 table (which should have TPS% ranging from 0% to 100%), then uses that to determine the fuelling based on the VE table. The advantage is that you can use different fuelling at different rpms (it also makes the blended MAP/alpha-N options possible).

  If you want basic alpha-N with the fuel dependent only on throttle position, just make the 6x6 tables equal the TPS% all the way across each row. Note that the default values might not be appropriate (they may be used to store other variables in some cases).

• Barometric Correction: This lets the user define a 6-element table of barometric correction (based on either the initial MAP value, or a second baro MAP sensor value). A 6 point table of baro pressure versus a correction change will allow you to modify the baro correction equation for your particular car, compensating for things like exhaust size. With this you can take EGO feedback versus barometric data at various elevations or barometric pressures. From this you can determine the % additional/ less correction you need to get your AFR where you want it. This does require that you add a second MAP sensor for baro. But you should be able to tune the table to give you a very stable AFR at any altitude.

  The baro correction is implemented as follows:

  barocor = baro correction from 2-point table + baro correction from new 6-point delta correction table

  Originally the MS-II code had a standard equation from the OEMs, and the 2 points in it were really just to calibrate the sensor being used. But some users said it was way off, although no one ever gave us a table of data that said, "I drove from this altitude to that altitiude at steady speed and load and this is what my wideband did vs the baro readings". So we added a 6 point table that was meant to force you to drive from altitude A to B and record baro and AFR at 6 points and then put the % delta correction into the new 6 point table. This should allow anyone to tune baro as perfectly as humanly possible. But for those who don't care about baro correction, the defaults for the 6 correction points are 0%, so nothing would break when using their previous setup.

  • File: This offers the usual fetch, burn, and exit options.
  • Tools/Curve Generate: This allows the user to generate a linear, exponential, or logarithmic curve automatically to fill in the 6-element table.

• Priming Pulse: If you have selected 'Table' for the 'Prime, ASE, WUE Tables' under 'Settings/General', then you can fill in a 10-element table for the priming pulse versus temperature (the pulse that occurs before MegaSquirt^® receives an rpm signal) instead of linearly interpolating between two points.
  • File: This offers the usual fetch, burn, and exit menu items that should be self-explanatory.
  • Tools/Curve Generate: This allows you to generate a linear, exponential, or logarithmic curve automatically to fill in the 10-element table.

• Cranking Pulse: If you have selected 'Table' for the 'Prime, ASE, WUE Tables' under 'Settings/General', then you can fill in a 10-element table for the cranking pulse width versus temperature (the pulse with that occurs while MegaSquirt^® is in cranking mode, generally under 300 rpm) instead of linearly interpolating between two points.
  • File: This offers the usual fetch, burn, and exit menu items that should be self-explanatory.
  • Tools/Curve Generate: This allows you to generate a linear, exponential, or logarithmic curve automatically to fill in the 10-element table.

• ASE Percentage: If you have selected 'Table' for the 'Prime, ASE, WUE, Baro Tables' under 'Fuel Set-Up/General', then you can fill in a 10-element table for the afterstart enrichment (ASE) versus temperature (the percentage of additional fuel added when MegaSquirt^® has transitioned from cranking mode to running mode) instead of linearly interpolating between two points.
  • File: This offers the usual fetch, burn, and exit menu items that should be self-explanatory.
  • Tools/Curve Generate: This allows you to generate a linear, exponential, or logarithmic curve automatically to fill in the 10-element table.

• ASE Taper: If you have selected 'Table' for the 'Prime, ASE, WUE Tables' under 'Settings/General', then you can fill in a 10-element table for the afterstart enrichment (ASE) taper versus temperature (the number of cycles during which additional fuel is added when MegaSquirt^® has transitioned from cranking mode to running mode) instead of linearly interpolating between just two values.
  • File: This offers the usual fetch, burn, and exit menu items that should be self-explanatory.
  • Tools/Curve Generate: This allows you to generate a linear, exponential, or logarithmic curve automatically to fill in the 10-element table.

• Realtime Display

  The realtime display (sometimes called the 'runtime display') shows the values of the tuning and control parameters inside the MegaSquirt^® controller in real time.

  Time (s)
  Time in seconds since MegaSquirt^® last booted ("secl"). This value is derived from the 8-bit seconds value in the internal MS clock, and will therefore only display values from 0 to 255 (it wraps around to zero when it hits 255). If the time wraps around before hitting 255, a reset has occurred, and this will be noted on the front page status bar. Note that with MegaSquirt-II, the datalogs will show secl continuing to climb above 255 (up to 65536), this is normal.

  Barometer (kPa and in/Hg)
  The barometric pressure as measured by MegaSquirt. Currently this is a static value determined at startup. Returned by MegaSquirt^® in "baro" as a raw ADC count.

  O2 (v)
  This is the voltage detected on the EGO sensor if on is installed. For narrow band sensors this ranges from 0-1 v and typical wideband sensors have a voltage range of 0-5 v.

  Coolant (F)
  The value reported by the coolant temperature sensor. By default, it has a maximum of 215°.

  Batt (v)
  Current battery voltage as measured inside MegaSquirt. If this number looks lower than actual battery voltage (probably 14.0 v or higher), then you may not have big enough wires running to MS; put a voltmeter across the wires from the board to their source in your vehicle's wiring loom (should be less that 1 v, a lot less). Returned from MS as a raw ADC count in "batt."

  TPS (v)
  Throttle position in volts. Most TPSs don't range all the way from 0 to 5 v, so don't be alarmed if yours only goes from 1.5 to 4.4 Volts as this is normal. The nominal TPS value itself is generally not interpreted in an absolute way, but rather the rate of change in TPS is what is used for acceleration enrichment. However the value of ~3.5 volts is used to denote "flood clear" mode; i.e., if you hold the throttle down past the 3.5 volt level (the voltage from the TPS) when cranking, the pulse width is cut back to 0.3 milliseconds.  Returned from MS as the variable "tps" in a raw ADC count.

  GammaE
  Gamma is the total enrichment factor, computed by MegaSquirt^® taking into account all of warmup, acceleration/deceleration, barometric, and manifold air temperature sensor correction factors, but excluding EGO correction, which is handled separately (See Corrections/Enrichments, below.) Returned from MS as a percentage value in "gammae".

  MAP (kPa)
  The manifold absolute pressure as seen by MegaSquirt^® in kiloPascals. Returned in MegaSquirt^® "map" as a raw ADC count, converted in TunerStudioMS using a hard-coded transfer function.

  MAT (F)
  The raw temperature of the air at the Manifold Air Temperature sensor. Used in conjunction with MAP to compute manifold air density. (See note on Coolant temp, above.) Returned by MegaSquirt^® in "mat" as a raw ADC count.

  RPM
  Engine speed in RPM. If this is jumping around in an unpredictable manner, you probably have a poor ignition signal input to MegaSquirt. It is returned from MS as RPM/100 in the variable "rpm."

  Pulse Width (ms)
  The injector pulse width being used by MegaSquirt^® to squirt fuel into your motor. Reported as 10xPulse width in the MegaSquirt^® variable "pw". 

  IAC DC (%)
  If a PWM Idle valve is selected, this is reporting the PWM percentage applied to the valve (0 to 100%). If a stepper motor IAC is selected, it reports the total number of steps made to extend the pintle, with 0 being the start value.

  Corrections/Enrichments (percent)
  This part of the realtime display shows all the individual correction factors used to compute gamma and the resulting pulse width.

  EGO
  This is the correction factor computed from O2 sensor readings. Returned as a percentage by MS in "egocorr". See "Exhaust Gas Oxygen" on the Enrichments page, below, for parameters to modify MegaSquirt's computation of this factor.

  Barometer
  A barometric correction is applied, based on the initial MAP sensor reading. Returned in "barocor" by MegaSquirt.
  
  Warmup
  The warmup correction factor applied due to startup and coolant temperature status. Returned in "warmocor" by MegaSquirt. See "Warmup Enrichment Bins" to modify the computation of this factor.

  Air Density
  Air density correction is computed from MAT. This value is returned from MegaSquirt^® in "aircor".

  Volumetric Efficiency
  The current computed VE value determined by look up in the VETABLE using RPM and MAP. Reported in "vecurr" by MegaSquirt.

  Acceleration
  Unlike all the other corrections here, the acceleration enrichment is an additive factor; take the result of all the above multiplied through, then add this one on. Returned from MegaSquirt^® in "tpsaccel".

  Runtime Messages
  This message is a decoded version of the MegaSquirt^® engine status variable "engine." Possible status values are (these are their names in the controller code megasquirt.h and megasquirt.asm):
  

  • Connected - TunerStudioMS is communicating with the MegaSquirt^® controller.
  • Cranking - whether the engine is cranking (i.e., RPM is less than 300).
  • Running - whether the engine is considered to be running or not.
  • Warmup - indicates that the engine is in warmup due to coolant temperature. You can change the TPS acceleration enrichment behavior by changing the "Warmup Enrichment Bins," below.
  • Afterstart - indicates if after-start warmup enrichment is being done (see Afterstart Enrichment in the next section).
  • ACCEL - tells us if MegaSquirt^® is applying acceleration/deceleration enrichment.
  • DECEL - indicates any acceleration enleanment (de-enrichment).
    

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• VE Table 1

  This window enables you to tune the VE table 'on the fly'. On the left are a number of gauges, and on the right are two items - a graphical representation of the VE table at the top, and a status box at the bottom.

  Cursor
  The "cursor" is the red cross on the tuning RPM vs MAP graph on the right half of the screen. The values corresponding to the current cursor position are displayed in the status window in the same color as the cursor. These represent the values that will be changed when the shift-up/down arrows are pressed.

  Spot
  The "spot" is the green dot specifying current engine operating position in the VE graph. The numeric values corresponding to the spot are displayed in green in the status window.

  Keystrokes
  

  • Arrows move the cursor.
  • Shift-Up (or Q) = richer at that point on the VE map.
  • Shift-Down (or W) = leaner at that point.
  • Ctrl-Shift-Up = increase ReqFuel by 0.1 ms.
  • Ctrl-Shift-Down = reduce ReqFuel by 0.1 ms.
  • F = Find and place cursor on map intersection nearest the spot.
  • G = Goto spot; continuous "F" mode.
  • Z = Zoom between a 2D and 3D display of the VE graph. 2D mode makes it much easier to see where the spot is with respect to the cursor, but 3D mode allows you to easily see when you have vertices that are out of agreement with the rest of the table.

  To navigate the VE map on the right of the Tuning screen, use the arrow keys move the tuning cursor, up moves up on the MAP axis of the grid and down moves to a lower MAP bin. If you know VI, then you can alternatively use the standard motion keys from that editor; use "k" to go up, "j" to go down, "h" to go left and "l" to go right. Left and right arrow keys move to the higher and lower RPM bins, respectively.

  The shifted up and down arrow keys richen or lean the VE table bin at the cursor. Alternatively, the "q" key richens the currently selected bin and "w" leans it. Whenever you change a value in TunerStudioMS, it is immediately changed in the MegaSquirt^® controller's RAM. These changes will go away when you turn off the engine if you do not save them into flash memory by typing "b" for "burn to flash."

  You can also easily modify the required fuel value on the tuning screen. Hold both shift and ctrl down while typing up and down arrow keys, each keystroke will change the value up or down by 0.1 ms.

  You can rotate the grid so you can see the values better on the 3D window more clearly. Hit the "m" and "n" keys and see what happens. Once you find an orientation you like, copy down the numbers that are displayed in the status window and you can set those as your defaults in the base ini file:

  gridOrient = 250, 0, 340 ; Space 123 rotation of grid in degrees. 
  

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• VE Table 2 (dual table mode only)

  This window enables you to tune the second VE table in dual table mode 'on the fly'. On the left are a number of gauges, and on the right are two items - a graphical representation of the VE table at the top, and a status box at the bottom.

  Cursor
  The "cursor" is the red cross on the tuning RPM vs MAP graph on the right half of the screen. The values corresponding to the current cursor position are displayed in the status window in the same color as the cursor. These represent the values that will be changed when the shift-up/down arrows are pressed.

  Spot
  The "spot" is the green dot specifying current engine operating position in the VE graph. The numeric values corresponding to the spot are displayed in green in the status window.

  Keystrokes
  

  • Arrows move the cursor.
  • Shift-Up (or Q) = richer at that point on the VE map.
  • Shift-Down (or W) = leaner at that point.
  • Ctrl-Shift-Up = increase ReqFuel by 0.1 ms.
  • Ctrl-Shift-Down = reduce ReqFuel by 0.1 ms.
  • F = Find and place cursor on map intersection nearest the spot.
  • G = Goto spot; continuous "F" mode.
  • Z = Zoom between a 2D and 3D display of the VE graph. 2D mode makes it much easier to see where the spot is with respect to the cursor, but 3D mode allows you to easily see when you have vertices that are out of agreement with the rest of the table.

  To navigate the VE map on the right of the Tuning screen, use the arrow keys move the tuning cursor, up moves up on the MAP axis of the grid and down moves to a lower MAP bin. If you know VI, then you can alternatively use the standard motion keys from that editor; use "k" to go up, "j" to go down, "h" to go left and "l" to go right. Left and right arrow keys move to the higher and lower RPM bins, respectively.

  The shifted up and down arrow keys richen or lean the VE table bin at the cursor. Alternatively, the "q" key richens the currently selected bin and "w" leans it. Whenever you change a value in TunerStudioMS, it is immediately changed in the MegaSquirt^® controller's RAM. These changes will go away when you turn off the engine if you do not save them into flash memory by typing "b" for "burn to flash."

  You can rotate the grid so you can see the values better on the 3D window more clearly. Hit the "m" and "n" keys and see what happens. Once you find an orientation you like, copy down the numbers that are displayed in the status window and you can set those as your defaults in the base ini file:

  gridOrient = 250, 0, 340 ; Space 123 rotation of grid in degrees. 
  	 

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• AFR Table 1 (Wide band O2 sensor only)

  This window enables you to tune the AFR table 'on the fly' if you have the wide band sensor option selected. On the left are a number of gauges, and on the right are two items - a graphical representation of the AFR table at the top, and a status box at the bottom.

  Cursor
  The "cursor" is the red cross on the tuning RPM vs MAP graph on the right half of the screen. The values corresponding to the current cursor position are displayed in the status window in the same color as the cursor. These represent the values that will be changed when the shift-up/down arrows are pressed.

  Spot
  The "spot" is the green dot specifying current engine operating position in the VE graph. The numeric values corresponding to the spot are displayed in green in the status window.

  Keystrokes
  

  • Arrows move the cursor.
  • Shift-Up (or Q) = leaner (higher AFR) at that point on the VE map.
  • Shift-Down (or W) = richer (lower AFR) at that point.
  • F = Find and place cursor on map intersection nearest the spot.
  • G = Goto spot; continuous "F" mode.
  • Z = Zoom between a 2D and 3D display of the VE graph. 2D mode makes it much easier to see where the spot is with respect to the cursor, but 3D mode allows you to easily see when you have vertices that are out of agreement with the rest of the table.

  To navigate the AFR map on the right of the Tuning screen, use the arrow keys move the tuning cursor, up moves up on the MAP axis of the grid and down moves to a lower MAP bin. If you know VI, then you can alternatively use the standard motion keys from that editor; use "k" to go up, "j" to go down, "h" to go left and "l" to go right. Left and right arrow keys move to the higher and lower RPM bins, respectively.

  The shifted down and up arrow keys richen or lean the AFR table bin at the cursor. Alternatively, the "w" key richens the currently selected bin and "q" leans it. Whenever you change a value in TunderStudioMS, it is immediately changed in the MegaSquirt^® controller's RAM. These changes will go away when you turn off the engine if you do not save them into flash memory by typing "b" for "burn to flash".

  Note that the AFR gauge on the left is showing you the current AFR of the exhaust gases according to the wideband feedback (and assuming it is set up correctly, etc.).
  The green lettering is showing you the table value at the current conditions. That is, it is showing you the target AFR. The gauge will only match this if the EGO correction is enabled and has sufficient range to get to the target level. Since you have the authority set to zero, you wouldn't expect them to agree.
  The red lettering is showing you the AFR from the table at the currently selected table position (i.e. the AFR of the table target value as you move around the 12x12 table). This is the table's target AFR value that will be adjusted if you choose to do that. It will be the same as the green value if the cursor is moved to the current operating conditions.
  So the gauge is showing you what you are getting, the green is showing what you are aiming for, and the red is showing you what you will change if you use the shift-up or shift-down arrow keys.

  You can rotate the grid so you can see the values better on the 3D window more clearly. Hit the "m" and "n" keys and see what happens. Once you find an orientation you like, copy down the numbers that are displayed in the status window and you can set those as your defaults in the base ini file:

  gridOrient = 250, 0, 340 ; Spatial rotation of 3-D table graphical view grid in degrees. 
  

  Return to help index

• AFR Table 2 (MS-II/Wide band O2 sensor/dual table mode only)

  This window enables you to tune the MS-II™ AFR table 'on the fly' if you have the wide band sensor option and the dual table mode selected. On the left are a number of gauges, and on the right are two items - a graphical representation of the AFR table at the top, and a status box at the bottom.

  Cursor
  The "cursor" is the red cross on the tuning RPM vs MAP graph on the right half of the screen. The values corresponding to the current cursor position are displayed in the status window in the same color as the cursor. These represent the values that will be changed when the shift-up/down arrows are pressed.

  Spot
  The "spot" is the green dot specifying current engine operating position in the VE graph. The numeric values corresponding to the spot are displayed in green in the status window.

  Keystrokes
  

  • Arrows move the cursor.
  • Shift-Up (or Q) = leaner (higher AFR) at that point on the VE map.
  • Shift-Down (or W) = richer (lower AFR) at that point.
  • F = Find and place cursor on map intersection nearest the spot.
  • G = Goto spot; continuous "F" mode.
  • Z = Zoom between a 2D and 3D display of the VE graph. 2D mode makes it much easier to see where the spot is with respect to the cursor, but 3D mode allows you to easily see when you have vertices that are out of agreement with the rest of the table.

  To navigate the AFR map on the right of the Tuning screen, use the arrow keys move the tuning cursor, up moves up on the MAP axis of the grid and down moves to a lower MAP bin. If you know VI, then you can alternatively use the standard motion keys from that editor; use "k" to go up, "j" to go down, "h" to go left and "l" to go right. Left and right arrow keys move to the higher and lower RPM bins, respectively.

  The shifted down and up arrow keys richen or lean the AFR table bin at the cursor. Alternatively, the "w" key richens the currently selected bin and "q" leans it. Whenever you change a value in TunerStudioMS, it is immediately changed in the MegaSquirt^® controller's RAM. These changes will go away when you turn off the engine if you do not save them into flash memory by typing "b" for "burn to flash". TunerStudioMS gives you the option of whether the values are burned to flash immediately or not.

  You can rotate the grid so you can see the values better on the 3D window more clearly. Hit the "m" and "n" keys and see what happens. Once you find an orientation you like, copy down the numbers that are displayed in the status window and you can set those as your defaults in the base ini file:

  gridOrient = 250, 0, 340 ; Space 123 rotation of grid in degrees. 
  

  Return to help index

• Spark Advance Table (adv_table):

  This window enables you to tune the MS-II ignition advance table 'on the fly'. On the left are a number of gauges, and on the right are two items - a graphical representation of the advance table at the top, and a status box at the bottom.

  Cursor
  The "cursor" is the red cross on the tuning RPM vs MAP graph on the right half of the screen. The values corresponding to the current cursor position are displayed in the status window in the same color as the cursor. These represent the values that will be changed when the shift-up/down arrows are pressed.

  Spot
  The "spot" is the green dot specifying current engine operating position in the VE graph. The numeric values corresponding to the spot are displayed in green in the status window.

  Keystrokes
  

  • Arrows move the cursor.
  • Shift-Up (or Q) = increased advance at that point on the VE map.
  • Shift-Down (or W) = decreased advance at that point.
  • F = Find and place cursor on map intersection nearest the spot.
  • G = Goto spot; continuous "F" mode.
  • Z = Zoom between a 2D and 3D display of the VE graph. 2D mode makes it much easier to see where the spot is with respect to the cursor, but 3D mode allows you to easily see when you have vertices that are out of agreement with the rest of the table.

  To navigate the spark advance map on the right of the Tuning screen, use the arrow keys move the tuning cursor, up moves up on the MAP axis of the grid and down moves to a lower MAP bin. If you know VI, then you can alternatively use the standard motion keys from that editor; use "k" to go up, "j" to go down, "h" to go left and "l" to go right. Left and right arrow keys move to the higher and lower RPM bins, respectively.

  The shifted down and up arrow keys increase or decrease the advance in the ignition table bin at the cursor. Alternatively, the "w" key richens the currently selected bin and "q" leans it. Whenever you change a value in TunerStudioMS, it is immediately changed in the MegaSquirt^® controller's RAM. These changes will go away when you turn off the engine if you do not save them into flash memory by typing "b" for "burn to flash".

  You can rotate the grid so you can see the values better on the 3D window more clearly. Hit the "m" and "n" keys and see what happens. Once you find an orientation you like, copy down the numbers that are displayed in the status window and you can set those as your defaults in the base ini file:

  gridOrient = 250, 0, 340 ; Space 123 rotation of grid in degrees. 
  

  In general, you want:

  • Low MAP (low engine load) = more spark advance
  • High MAP (high engine load) = less spark advance
  • Low CLT (cold engine) = more spark advance
  • High CLT (warm engine) = less spark advance
  • Low RPM = less spark advance
  • High RPM = more spark advance
    
  To set the spark advance table, you should try to understand what your engine needs in the following areas:
  1. total advance at WOT: should be from ~24° to ~40° depending on your bore size and combustion chamber characteristics. Older design engines (i.e. push rods, domed pistons, etc.), and those with large bores (big blocks, etc.) need more advance, about 36 to 38°. Newer designs (4 valve/cylinder, swirl port engines, etc.), and small bores, generally require less, about 28 to 32°. Engines that have a lot of miles on them require less as well, because of oil leakage into the chamber. Lower octane fuel also requires less advance (it burns more quickly), so if you are running 87 octane, use a few degrees less total advance than if you are running 94 octane.
  2. RPM based advance: Generally for a performance engine, you want the advance to be 'all-in' by 3000 rpm. So for a given MAP (say 100 kPa) the spark advance should rise from the initial value to the maximum by about 3000 rpm, then remain constant.
  3. vacuum (MAP) advance: as the load on the engine is reduced, the fuel burns more slowly and more advance is required. This means that you should have the advance increase for a given rpm as the MAP value decreases in kPa. So, for example, if you have 32° advance at 4000 rpm and 100 kPa, you might have 40° advance at 4000 rpm and 50 kPa. You can make the intervening values evenly spaced to begin with, and tune them later. You can experiment by using up to 10° to 20° more advance at the lowest kPa bins compared to the highest kPa bins.

Return to help index

• Warmup Wizard

  In this dialog you can set the warm-up enrichment (WUE) bin values and a few other related settings. The WUE bins are used to provide additional fuel during warmup, much like a 'choke' on a carburetor. A WUE value of 100 means no enrichment. Typically values are 100% at the highest temperature (usually 160°F) and increase up to around 160 or more by -40°F. Setting a warmup enrichment bin to 100 (usually the last one, but you can set it to 100% at other bins too) disables the warm-up enrichment. You can edit the temperature bins themselves, as well (see this).

  Some things to be aware of:

  1. Note that the ASE and prime pulse values are grayed out in the warm-up wizard for some firmware releases. They are listed under 'Fuel-Set-Up/AfterStart Enrichment' or 'Fuel-Set-Up/Other Fuel Settings' if you have chosen 2-point over tables for the 'Prime, ASE, WUE, baro Tables' under 'Fuel Set-Up/General'. If you have chosen 'Tables' see the items under 'Other Tables'. The items are missing from the warmup wizard because there are no INI 'adjustments' for the warm-up wizard, and the hard-coded warm-up wizard only allows 1-point values to be changed. Since the code now only has 2-point or tables, displaying the 1-point values is quite misleading.

  Return to help index

• Acceleration Wizard

  Acceleration enrichment (AE) occurs when you open the throttle "rapidly" to avoid bogging the engine. In v.1.01 MegaSquirt^® EFI Controller, this is done solely based upon the rate of change in the throttle position sensor (also called TPSDOT).

  MegaSquirt-II allows this acceleration enrichment to be triggered by a change in the TPS (TPSdot) or a change in the MAP (MAPdot) or any combination of the two.

  The MAPdot settings are on the left side of the accel wizard, and the TPSdot settings are on the right. Each column of 4 bins allows you to specify the rate of MAPdot or TPSdot, and in the corresponding bin (to it's right) you can specify the amount of fuel (in milliseconds per injection) that should be added to the pulse width calculated based ont he MAP, rpm, etc.

  Acceleration Enrichment Bins (ms)
  These bins specify the actual enrichment in terms of pulse width. They are linearly interpolated to determine a value that is ultimately added to the computed pulse width. The array of values is called "TPSAQ" as stored in MegaSquirt. Note that with MegaSquirt-II, you have two sets of bins, one for TPS based acceleration enrichment, and the other for MAP based acceleration enrichment.

  You can use the slider to choose between the TPSdot and MAPdot accel enrichments. Move it to the left to select more MAPdot accel enrichment, and to the right for more TPSdot enrichment.

  Below the accel bins are a number of other settings:

  MAPdot Threshold
  This is the threshold in kPa/sec below which no acceleration enrichment will occur (you can move the throttle from idle to full open without acceleration enrichment, if you open it slowly enough). A typical value is 80 kPa/sec. Tuning Note: While you are tuning the VE table you should set this threshold artificially high (maybe 150.0) to disable acceleration enrichment completely. After the VE table is fairly well-defined, set this back to 80 and begin tuning AE.

  TPSdot Threshold
  This is the threshold in %/sec below which no acceleration enrichment will occur (you can move the throttle from idle to full open without acceleration enrichment, if you open it slowly enough). A typical value is 15%/sec.

  Note that if you have tuned this value and have it set to your satisfaction, this change won't affect your tune, it will simply be displayed as 10x larger.

  Accel Time (sec)
  This value indicates how long the acceleration enrichment "squirt" will last. Typical values are around 0.3 second. MegaSquirt^® stores this value in the variable "TPSACLK".

  Accel Taper Time (sec)
  This value indicates how long after the 'Accel Time' that MegaSquirt^® tapers the acceleration enrichment from the 'bin value' to the 'End Time'. enrichment "squirt" will last. Typical values are around 0.2 second. MegaSquirt^® stores this value in the variable "TPSACLK".

  End Time (sec)
  This value indicates how long the acceleration enrichment will be after the 'Accel Time' + 'Accel Taper Time'. Typical values are around 0.5 millisecond. MegaSquirt^® stores this value in the variable "TPSACLK".

  Cold Accel Enrichment (ms)
  The acceleration enrichment pulse also varies depending upon coolant temperature. The value specified here is the pulse width added to the value from the bin calculations at -40 F. The Cold Acceleration Enrichment amount is linearly interpolated from full amount at -40 F down to zero at 165 F. A typical value might be 2.0 ms. This value is stored in the "TPSACOLD" variable in MegaSquirt.

  Cold Accel Multiplier (%)
  Another means for increasing the amount of fuel delivered by the acceleration enrichment pulse is supplied by this value; it is likewise interpolated from the full specified amount at -40F down to zero at 165 F. Before the Cold Acceleration Enrichment value is added to the base acceleration enrichment pulse width, it is multiplied by this value. Total AE = Base AE * CAM + CAE The difference between the two types of AE cold modify can be easily seen with a few examples:

  1) Assume we have a calculated AE pulse of 5.0 ms. Say our coolant temperature is 40 F, giving a CAE pulse of 2.0 ms and CAM is turned off (100%). The result is 5.0+2.0 = 7.0 ms.

  2) Assume same base AE and temperature, but now we turn off CAE (0.0 ms) and set CAM to give 140%. The result is the same, we get 5.0*1.4 = 7.0 ms.

  3) Take the first case, but hit the accelerator faster, giving 8.0 ms base AE pulse. We now have a result of 8.0+2.0 = 10.0 ms.

  4) Take case 2, but with the higher base AE pulse, giving 8.0*1.4 = 11.2 ms. The bottom line is that the CAE modifier is constant and independent of the base pulse, where on the other hand, the CAM modifier has a proportional effect on the AE, bigger base pulse means bigger result. This value is stored in the "ACMULT" variable in MegaSquirt.

  Decel Fuel Amount (%)
  When you let off the throttle rapidly (that is the closing rate exceeds TPSDOT Thresh) and the engine is turning faster than 1500 RPM, then deceleration fuel cutoff is performed by MS. Deceleration fuel amount is multiplied by the "normal" pulse width, that is, if the calculated pulse is 12.0 ms and you have 20% decel amount, then the resulting pulse width is 2.4 ms. A value of 100% causes the fuel to remain at its calculated value, and can cure bucking on deceleration in vehicles with manual transmissions; those with automatic transmissions may benefit in fuel economy by using values below 100%. The MegaSquirt^® variable "TPSDQ" holds this value as a percentage.

The concept of "X-Tau" compensation is very simple: for every squirt of the fuel injector, the majority of the fuel makes it into the cylinder, but some of the fuel from the squirt collects on the wall of the intake manifold and intake valve. In simplistic terms, a certain percentage of fuel (1-X) gets into the cylinder, the remainder sticks to the walls (X), hence the term 'wall wetting'.

The fuel that sticks to the walls eventually evaporates back into the airstream and is drawn into the cylinder. This is a time variable, call it Tau, which is the amount of time it takes to get the fuel clinging to the wall back into the cylinder.

Both X and Tau can be a function of RPM/MAP, coolant temp, etc. X value is pretty much constant but the Tau is a function of several parameters.

Note that if the injection pulse width is the same, and if it arrives with a fixed time interval (i.e. same RPM) then a equilibrium is reached where the amount of fuel sticking to the walls is in equilibrium with the wall film dissipating back into the airstream. However, a change in pulse width or a change in the time between injections upset this equilibrium, requiring an "adjustment" in the delivered fuel if one wants to compensate, hence the term "transient fuel compensation".

There is more on X-Tau here: www.megamanual.com/ms2/xtau.htm.

There are a number of user-configurable settings for X-Tau. If X-Tau is enabled under 'Settings/General/X-Tau Usage', then you'll find:

• Puddling Factors (accel): This is the percentage of the increased fuel (0-100%) from a lengthened 'squirt' that goes into wall puddling while accelerating (fuel pulse width increasing), with the remainder of the squirt going directly into the cylinder to be burned.
• Puddling Factors (decel): This is the percentage of fuel (0-100%) going into wall puddling while decelerating (fuel pulse width decreasing),
• Time Factors (accel): MS-II™ implements a RPM-dependent factor for Tau due to the fact that at higher RPM fuel is pulled into the chamber which reduces the puddle mass. This info came from research from Jim Cowart who spent 4 years researching this under John Heywood at MIT (for his PhD Thesis) - he has been instrumental in assisting us directly with algorithm refinement (event-based MAP sampling is another recent improvement that was prompted by him - a lead-in for model-based control).
• Time Factors (decel):
• X (Puddling) Temp. Corrections: 1x10 table for coolant temperature (CLT) correction to the puddling factor X.
• Tau (Time) Temp. Corrections: 1x10 table for coolant temperature (CLT) correction to the time factor Tau.
• MAPdot Settings: This sets the MAP dot threshold and prediction parameters:
  • MAPdot Thresholds: The two MAPdot thresholds work as follows: if MAPdot is above the start transition threshold, the X-Tau accel tables are used. If MAPdot is less than (i.e., more negative than) the finish transition threshold, the the X-Tau Decel tables are used. If MAPdot is in between, a blend of the 2 tables is used.
    • Start Transition:
    • Finish Transition:
    Note that these are in negative kPa (i.e., put 40 if you want the threshold to be at -40 kPa/sec).

  • MAP trending: The map trending senses a change in MAP (kPa) and adds a bit more to the MAP value in anticipation of even more air actually being there because there is a small delay in the MAP sensor. This higher map that results from the trending causes X-Tau to kick in faster. It just for really quick stabs.
    • MAPdot Trending Threshold:
    • Max. MAP added per sample:
• RPM Values: These are the RPM bins used in the X-Tau calculations. You may need to tune these for your specific engine and application. Note that changing the RPM bins effectively changes the X and T factors, so you should set the RPM bins early in the X-Tau tuning process.

• Cold Advance

  This is a table that is used to increase the ignition advance at lower coolant temperatures. Because cool mixtures burn more slowly and are less likely to detonate, additional spark advance at lower temperatures can help the engine to run better and more efficiently.

  The ten element cold advance table lets you specify this additional advance. Typically, a total of about 6° degrees is added at -40°F, and you should be sure to use 0° at fully warmed up temperatures (otherwise this will be added to your advance table).

• IAT-based Fuel Correction

  Some users have found that the ideal gas law calculation of air mass does not work especially well for them. This could be because the air entering the cylinder does not reflect the measured temperature. The IAT fuel correction table lets the user define a 6-element table of IAT (intake air temperature) corrections top the fuel amount.

  • File: This offers the usual fetch, burn, and exit options.
  • Tools/Curve Generate: This allows the user to generate a linear, exponential, or logarithmic curve automatically to fill in the 6-element table.

• IAT-based Timing Retard

  This is a table that is used to reduce the ignition advance at higher intake air temperatures. Because hot mixtures (typically from the heated air from a supercharger or turbocharger) burn more quickly and are more likely to detonate, reducing spark advance at higher intake air temperatures can help the engine to run better and avoid destructive detonation.

  The ten element MAT-based retard table lets you specify this reduced advance.

• Idle Steps (stepper IAC only )

  This table tells MegaSquirt-II how to position the IAC stepper motor at various temperatures. There are ten temperature bins.  At start-up, MegaSquirt-II 'retracts' (opens) the stepper motor by the number of steps specified in the 'Idle Control/Start Value' field. The number specified in this table are how many steps the stepper closes when the coolant temperature reaches the specified temperature. So if you want the stepper to be completely closed at idle, you would set the last bin (160°F) to equal the start value.

• Idle PWM Duty Cycle  (MegaSquirt-II / PWM idle valve only )

  For those that have PWM style idle valves (typically Ford, as well as others), this is the ten element table that specifies the duty cycle (in percent) at each of ten temperatures. Generally, higher temperatures require higher duty cycles.

• Alpha-N MAP Table (Alpha-N only )

  This is the MAP table that is used for alpha-N fuelling computations when the hybrid alpha-N option is selected.

• MAF Correction Table 

  If you select one of the MAF options, you must input a MAF sensor calibration curve (or use the default Ford curve). This is similar to the coolant sensor curve, in that both are non-linear and can not be handled as a simple scale and offset. The best way to obtain such a curve is by measuring the air flow through a flow bench. In doing this it is vital that the entire air duct be included in the measurement. If this is not feasible, then a shorter correction table is provided as a tuning input. This table consists of MAFFlow vs % correction arrays, where as usual 100% means no correction. The final MAF is calculated by:

  1. Reading the ADC and obtaining a rough MAF value from the sensor calibration curve.
  2. Using this rough value to obtain a correction factor by interpolating in the MAFFlow vs Correction tables.
  3. The final MAF is the rough MAF x %Correction / 100.

  Here is more information on tuning the MAF curve.

• Calibrate TPS

  One of the first things you should do after installing TunerStudioMS is set up the throttle position file. This is pretty simple, you need to turn on the MegaSquirt^® controller (don't start the engine!), go to the Tools menu and select Calibrate TPS. Leave the throttle closed and pick the Get Current button for closed position, push the pedal to the floor (this is why the engine MUST NOT BE RUNNING) and pick on the Get Current button for wide open throttle. Click OK and you're done. Whenever you change the TPS or mess with the throttle body, just go through this procedure again.

• Calibrate Thermistor Tables

  For each of the coolant (CLT) and intake air (IAT) temperature sensors, this utility lets you specify the resistance of the sensor at 3 different temperatures (along with a bias resistor value) which allows you to use non-standard temperature sensors (the defaults are for the standard GM sensors).

  TunerStudioMS doesn't save the values you enter into the dialog used for the AFR calibration, and neither does the MegaSquirt^® controller. Instead, the actual table values are burnt (and the controller remembers them even if the power is shut down). So you select the thermistor parameters you want, TunerStudioMS calculates the values to burn and then burns them (allow time for it to complete writing the 1024 entries). You should get the right temperature readings.

  Next time you go into the thermistor calibration menu, the parameters you used last time are NOT displayed (because neither TunerStudioMS nor the MegaSquirt^® controller store these values), however the thermistor table is still in place and should give the correct readings.

  IMPORTANT NOTE: Do NOT burn tables ('Calibrate AFR Table' or 'Calibrate Thermistor Tables') on a running engine. Even idle is NOT allowed, because these tables ONLY exist in flash, so once a table is erased, there is nothing but garbage in there until it is re-programmed, one word at a time. Until that reprogramming is complete, operating the engine is unsafe.

• Calibrate AFR Table

  To have MegaSquirt-II™ recognize your EGO sensor, you need to go to 'Tools/Calibrate AFR table' in TunerStudioMS and choose the appropriate selection for your oxygen sensor/controller, then click 'OK'. This will download the Volts versus AFR table to MegaSquirt-II™, and will dictate what TunerStudioMS reports in terms of both volts and AFR.

  TunerStudioMS doesn't save the value of the menu selection you used for the AFR calibration, and neither does the MegaSquirt^® controller. Instead, the actual table values are burnt (and the controller remembers them even if the power is shut down). So you select the AFR you want to burn and then burn it (allow time for it to complete writing the 1024 entries). You should get the right AFR readings.

  Next time you go into the AFR calibration menu, the AFR selection you used last time is NOT highlighted (because neither TunerStudioMS nor the MegaSquirt^® controller store this value), however the AFR table is still in place and should give the correct readings.

  IMPORTANT NOTE: Do NOT burn tables ('Calibrate AFR Table' or 'Calibrate Thermistor Tables') on a running engine. Even idle is NOT allowed, because these tables ONLY exist in flash, so once a table is erased, there is nothing but garbage in there until it is re-programmed, one word at a time. Until that reprogramming is complete, operating the engine is unsafe.

• Calibrate MAF Table

  To assist in the calibration and use of Mass Air Flow sensors, an analysis program has been developed to aid in the characterization of MAF transfer curves. This Windows program is called the MAF Analyzer and is available for download here:

  MAF_analyzer_V1.0.zip

  You can re-calibrate the software to use different 1024 element tables to derive airflow from the MAF sensor output.

  To assist in the calibration and use of Mass Air Flow sensors, an analysis program has been developed to aid in the characterization of MAF transfer curves. This Windows program is called the MAF Analyzer and is available for download here:

  MAF_analyzer_V1.0.zip

  To use the program, simply unzip in an empty directory and double-click on the application to execute - please read the user's manual for the MAF Analyzer included in the archive above. Below are some links for pre-run files that can be uploaded to MS-II™/MicroSquirt^®/s:

  1. Ford Lightning MAF,
  2. Infiniti Q45 MAF,
  3. GM LT1/LS1/LS2 MAF.

  To load the files to your MegaSquirt^® controller, place the file in the project folder's \inc\ sub-directory. This directory might already exist, or you may have to create the directory. You should rename the file you want to load to 'maffactor.inc'. Then, in TunerStudioMS, go to 'Tools/Calibrate MAF Table' and click the 'Write to Controller' button. TunerStudio will show the progress as the table is written to the controller.

  You can have more than one MAF .inc file in your \inc\ sub-folder (more recent versions of TunerStudioMS have these built in as defaults with the files already in place - if they aren't in place, just copy the files above to the project folder's \inc\ sub-folder).

  You can select between them in TunerStudioMS (that is why there is the 'Select Settings' test in the TS MAF burning dialog - a drop down selection box will appear if more than one file has been defined). To define more files this, you must edit the INI file where it says,

  [ReferenceTables]
  
    tableWriteCommand 	= "t" ; 
    
    referenceTable = mafTableBurner, "Calibrate MAF Table..."
    	;topicHelp = "http://www.megamanual.com/mt28.htm#??"
      tableIdentifier = 003, "MAF Table"
      adcCount 	= 1024 	; length of the table
      bytesPerAdc 	= 2 	; using words
      scale		= 1 ; scale before sending to controller
    	solutionsLabel	= "MAF Sensor"
    	solution	= "MAF Sensor", 	{ table(adcValue, "maffactor.inc") }
  

  and add lines that define new file names that have been placed in the project's \ini\ folder, like:

    	solution	= "Ford Lightning MAF", 	{ table(adcValue, "maffactor_1L3F_Lightning.inc") }
  		solution	= "Infiniti Q45 MAF", 		{ table(adcValue, "maffactor_Q45.inc") }
  		solution	= "GM LT1/LS1/LS2 MAF", 	{ table(adcValue, "maffactor_lsx.inc") }
    	etc.
  		

• Sensor Calibration

  This allows you to use 'non-standard' MAP and barometric sensors, as well as in some cases to adjust the amount of barometric correction.

• Trigger Wizard

  Before tuning your advance table, be sure to use a timing light to verify that your 'trigger offset' is calibrated. Changing the Trigger Offset in TunerStudioMS will not change the displayed advance, instead, it changes the actual advance as seen with a timing light. Your goal is to make these two match.

  To do this, get your engine warmed-up (otherwise the timing moves as the temperature increases) and idling, then use a timing light to verify to be certain your actual advance as shown by a timing light equals your the advance display on the advance gauge in TunerStudioMS. (26.3° in this case). (Note that positive numbers denote BTDC, and negative numbers denote after TDC.)

  

  The trigger offset value can theoretically be set anywhere physically, however, since it may be used for cranking and 'fault mode' timing (GM 7-pin HEI), it is best to set it at a reasonable number for idle, say ~8° BTDC (or whatever is recommended by the module's manufacturer). Check this with a timing light. To get the trigger offset to this value, you may have to rotate your distributor or move your crankshaft VR sensor.

  The trigger offset is a quick way to move the entire table around. This could help in for example dyno tuning if you wanted to see in one run what retarding everywhere did to you, then start moving things around according to the horsepower curve compared to baseline with 0° offset.

• Injector Test Mode

  This is a special mode designed for flow testing and/or cleaning injectors using MegaSquirt-II as a driver. Bruce and Al get several inquiries a week on the JectorRate FI driver setup, enough that we think that adding this mode will be useful.

  Gasoline is dangerous, especially in vapor form. If you use gasoline, it should be in a 'closed system' (One that does not allow vapors or liquid to escape). Be sure to have at least two fire extinguishers on hand, and keep them physically separated so the you will always have a clear path to at least one. Consider using other fluids than gasoline for testing. See this page: www.not2fast.com/efi/injector_info.shtml for some alternative fluids.

  To activate the test mode, you set the 'Injector Test Mode' to 'Test Mode', burn it to flash ("Burn to ECU") and cycle power. To get out of test mode you just turn off the option in TunerStudioMS - you don't have to burn it. The code burn the 'normal mode' setting automatically and then reboots itself, coming up in normal mode.

  There is also a 'Repeat Mode' which means to repeat the number of squirts you just. The code resets the Test Mode and repeats. The user can keep sending 'Repeat Mode' (up to 127) if that's easier and the code will keep repeating the number of squirts. Or users can just cycle power without turning off the Test Mode, which is just as easy unless your full time job is testing injectors.

  Injector test mode sets up a specific injector pulse width, duty cycle, and an adjustable commanded number of pulses. So, an injector can be plumbed up on a test stand with test fluid, and the injector exercised for a specific number of pulses/widths. And the injector open time and PWM current limit will still be there, so these can be characterized in the flow. The test fluid volume can be measured, alternatively the mass change introduced by the fluid can be measured on a sensitive scale.

  The injector test mode allows you to set up:

  • Injector test squirts, the total number of squirts,
  • Injector test pulse width per squirt(milliseconds), you can enter up to three decimal places, and
  • Off time, which is the time between squirts.

  Note that flow values will be most accurate for longer pulse widths (up to 65 milliseconds), BUT if you are testing low impedance injectors they will flow too much current at longer pulse widths without some form of current limiting. Since the injector test mode has PWM current limiting, you can use long pulse widths with the test mode, IF YOU HAVE SET UP THE PWM PARAMETERS. See this link for information on how to do that: www.megamanual.com/ms2/configure.htm#pwm.

  To test the injectors, enter the number of squirt, pulse width, etc., you want, then cycle the power to MegaSquirt^® to start the test. The MegaSquirt^® will fire the injectors for:

  Time = Injector test squirts * (Injector test PW + Off time)

  For example, for injector test squirts = 400, Injector test PW = 20.000 and Off time = 60), the total duration of the test is:

  Time = 400 * (0.020 + 0.060) = 32 seconds

  If you collected 38cc of fuel from 2 injectors during this time, and they had an opening time of 1.0 milliseconds, the flow rate would be:

  FlowRate (total) = 60 * Volume/(Injector Test Squirts * (Injector test PW - Opening Time))
  FlowRate = 60*38cc/(400 * (0.020-0.001)) = 300 cc/min

  Since this is for two injectors, the injectors flow 150 cc/min each.

  When the test is complete, test mode then sits there waiting for either a reset command from TunerStudioMS or you can change the test option and reset to resume normal mode. This could be used on the bench for commercially testing/cleaning injectors or to clean/test them in your car by pulling out the injectors from their pockets and letting them squirt into a can. The cost of a complete MS-II™ fully assembled is still way cheaper than a commercial tester/cleaner.

  There is more information here: www.megamanual.com/ms2/injectortest.htm.

• Configure CAN Outmsg

  TunerStudioMS has the ability to burn new outmsg formats to the MegaSquirt^® controller to allow it to pass different information to various CAN devices. This function is under menu item 'Tools/Configure CAN Outmsg'.

  The formats are defined in a file called canOutmsg.inc, here is an example: canOutmsg.inc. This file should be placed in the Project folder's \inc\ sub-directory. The file format for the default CAN outmsg is:

  ; CAN Outmsg
   DW 0       ; xrate, .128 tics
   DW 156      ; lsb
   DW 18       ; no_bytes (0-255)
   DW 19       ; dest id = 1 << 4 + varblk = 3
   DW 6       ; rpm offset (2 bytes)
   DW 7
   DW 8       ; adv offset (2 bytes)
   DW 9
   DW 18       ; map offset (2 bytes)
   DW 19
   DW 20       ; mat offset (2 bytes)
   DW 21
   DW 22       ; clt offset (2 bytes)
   DW 23
   DW 24       ; tps offset (2 bytes)
   DW 25
   DW 28       ; afr1 offset (2 bytes)
   DW 29
   DW 32       ; knock offset (2 bytes)
   DW 33
   DW 64       ; maf offset (2 bytes)
   DW 65
   DW 0	       ; nothing
   DW 0	       ; nothing
   ...
   

  Where the variables are grabbed from the Outpc structure (look at the [OutputChannels] section of your code's INI for a complete listing) at the offsets listed (6,7,8, ... 32,33,64 & 65).

  1. The first line is a comment to identify the file and make any notes.
  2. The second line and third lines (DW 0 & DW 156 = 0*256 + 156 = 156) are the transmit rate. 0 means the message is only transmitted when requested, otherwise it indicates the clock speed in 0.128 tics at which a CAN message will be transmitted automatically after receiving a request for data.
  3. The fourth line (DW 18) contains the total number of bytes to be transferred. This excludes the xrate, no_bytes and destination ID. Must be <= size of outpc and <= 255.
  4. The fifth line specifies the destination table ID (i.e., in which table the receiving CAN device stores the received values). You must specify a value that is 16 more than the actual table ID, so 19 indicates table 3, 25 indicates table 9.
  The transmitting and receiving controller must have the same outmsg structures, and they can have up to 8 of them on each controller.

  You can have more than one Outmsg .inc file in your \inc\ sub-folder, and select between them in TunerStudioMS (that is why there is the 'Select Settings' test in the TS Outmsg burning dialog - a drop down selection box will appear if more than one file has been defined). To define more files this, you must edit the controller's INI file where it says,

  [ReferenceTables]
  
  ...
  
    referenceTable = canOutmsgBurner, "Configure CAN outmsg..."
    	;topicHelp = "http://www.megamanual.com/mt29.htm#outmsg"
      tableIdentifier = 010, "outmsg Table"    ; id in octal, 010 = table 8
      adcCount 	= 1024 	; length of the table
      bytesPerAdc 	= 1 	; using bytes
      scale		= 1 ; scale before sending to controller
    	solutionsLabel	= "CAN Outmsg"
    	solution	= "CAN Outmsg", 	{ table(adcValue, "canOutmsg.inc") }
  

  and add lines that define new file names that have been placed in the project's \ini\ folder, for example:

    	solution	= "MShift Outmsg", 	{ table(adcValue, "MShift_Outmsg.inc") }
    	etc.
  		

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• MS-II Info

  Al Grippo and Bruce Bowling have created MegaSquirt-II, which is a plug-in daughter card that replaces the 8-bit MC68HC908GP64 with a 16-bit MC9S12C64 processor. MegaSquirt-II is an intermediate step from the original MegaSquirt^®.

  It is basically a plug-in processor card that has the MC9S12C64 processor plus support hardware as well as a stepper motor chip, and an ignition module controller. The embedded code is written in C, rather than assembly language, so it should be more accessible to more programmers.

  For current documentation, go to www.megamanual.com/ms2/, or for support questions visit http://www.msefi.com/.

• Injector Characteristics
• Sensor Calibration