• 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 MegaTune:
    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: Once the controller has sync'ed the input signals, it doesn't necessarily have to check for sync again. The code knows how mant teeth there are on the crank wheel, and can keep track of which cycle the crank is on after that. However, you can specify how often the controller should check that the engine is still sync'ed. The options are:
    • "Check Only at Steady Speed",
    • "Check Accel and Steady Speed",
    • "Check Decel and Steady Speed",
    • "Check Always".

  • 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. (set this to 0 for no wheel decoding).

  • Missing Teeth (No_Miss_Teeth): Number of consecutive missing teeth. That is, the size of the gap in the wheel's teeth, measured in terms of the number of regular teeth (high part and low part) that would have fit in the gap.

    If you set this to zero (like a Mazda KLDE 6-0 crank wheel, for example) then you must choose one of the dual spark options to recognize the cam sync signal:

    • Falling Cam Sync with Tach or Wheel, or
    • Rising Cam Sync with Tach or Wheel

    If you have a single ignition module (like the KLDE), and your module requires a high signal for the dwell period, you must then tie the dual outputs together with a logic 'OR' circuit. The circuit will prevent the ignition outputs from short-circuiting the processor outputs when one is trying to pull the signal high, and the other is trying to pull the signal low. This is done with a 'forward' diode on each output. 1N4001 diodes, or similar, will work fine. The banded end of the diode goes on the module side of each ignition output, a 100K &Ohm; resistor is used to pull the signal to ground, then the wires are joined and connected to the module's spark input.

    Here is a schematic of a logic OR circuit (high if either IGN1 or IGN2 are high, low otherwise; use if the dwell period of the signal for the ignition module needs to be high):

    

    Here is an schematic of a logic AND circuit (high only if both IGN1 or IGN2 are high, low otherwise; use if the dwell period of the signal for the ignition module needs to be low):

    

    There is more on tieing the IGN outputs together here: www.microsquirt.info/dualspark.htm

    Note that the cam input and second ignition output only come on MicroSquirt^® controllers, though in theory it is possible to add them to a V3 main board with some DIY work.

    Note that an N-0 wheel can also be run in (crank wheel) wasted dual spark mode with a Rising/Falling crank synch - these are the last dual spark 2 modes ('N-0 Wheel w/ Falling Crank Sync' or 'N-0 Wheel w/ Rising Crank Sync').

  • 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: Dual spark options are primarily for MicroSquirt^® controllers, which has dual ignition inputs and outputs. In theory these outputs can be added to a V3 main board with some DIY work.
    • 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 ** NO injector PWM ** with this option. Also, NO trigger return, NO wheel decode, NO EDIS. Also set ISR_tmask=0,_pmask < 20. The inputs are from 2 or 4 cyl crank or 4 cyl cam. They are in- dependent, 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 inj pwm, NO trig_ret, No EDIS. On MicroSquirt^® EFI controller, cam_sync must fall inside missing tooth gap; with the MS-II Sequencer board cam_sync can come anywhere after Cam_Tooth and before 1st tooth after missing gap.

    • Single Crank Wheel Input is same as 2,3 but 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 MegaTune ini files, it won't allow it, so use the latest 2.8 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.

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• 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.
    • Threshold (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'.
    • Peak (V) 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 MegaTune, 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".

  Return to help index

  • 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 MegaTune 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.

  Return to help index

• 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.

• Tuning
  • 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 MegaTune 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 - MegaTune 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 MegaTune, 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. 
    

    Tools/Autotune

    Autotune is an algorithm built into recent releases of MegaTune that automatically tunes your VE table based on EGO feedback. It is similar to MSTweak3000, but operates in real-time, without a datalog, and on any variant of code and processor that uses MegaTune.

    The VE value inside MegaSquirt's RAM memory is modified and your engine feels the effect immediately, but it is not burned to flash and made 'permanent' until you click "Burn Table". If you do not burn the table, the changes will be lost the next time the power is cycled on MegaSquirt.

    With a narrow band sensor, you can use auto-tune with any algorithm and any sensor to tune the low-power part of the table, it will get you to stoich (or AFR targets) quite nicely, which will give you a starting point from which to extrapolate the high-power part.

    You don't need a dynomometer to get the high output regions of the VE table done, but you definitely should NOT use auto-tune with a narrow band sensor for that part of the table, you'll end up with broken or melted pistons. In order to use auto-tune for WOT tuning, you must be running a wide band lambda system (sensor and controller), with an appropriate EGO correction algorithm that allows you to set specific AFR targets (i.e., MS-II). If one of these requirements is missing, then you must rely on seat-of-the-pants and experience.

    To enable autotune, select 'Tuning/VE Table1/Tools/Autotune'. An autotune status text indicator will appear in the message window in the lower right corner of MegaTune. Note that auto-tune updates the VE table in RAM, and requires that you click "Burn" to save the changed VE table permanently.

    Beware that if you go so rich that you start to see misfires, the lambda sensor will read the unburned mixture as dead lean (since unburned oxygen is present) and the closed loop algorithm will attempt to add fuel, which the auto-tune algorithm will detect and adjust the VE bin richer, thus making a bad situation worse. Use with caution, auto-tune will not perform magic!

    Typically, acceleration enrichment and decceleration enrichment happen while the engine RPMs are changing quite rapidly, and they usually turn off EGO correction at the same time, pretty much negating those two conditions.

    To start with, set the EGO step size (in MegaTune) to 1%, and set the authority down to ~10%, so that auto-tune doesn't do unstable jumps. The default auto-tune gain is 50%, so if you could jump a VE entry by as much as 5% in a single operation with the above numbers.

    The EGO control algorithms all turn off correction (i.e., set the correction factor to 100%) whenever AE, decel, warmup or any number of other enrichment types come active. The 100% EGO value in turn has the effect of turning off the auto-tune.

    The EGO correction step doesn't come into play at all, that's only internal to the EGO algorithm itself and dictates how rapidly it moves when correcting. The auto-tune step is determined by the current EGO correction (which is limited by the EGO controller authority), and the proportional gain, so only those two values really play a role in computing how big the auto-tune step will be. So, things proceed like this:

    1. The EGO algorithm uses whatever means necessary to come up with a number, this is limited to 100% +/- EGO authority with the familiar algorithms.
    2. The auto-tune algorithm uses the EGO correction value from 1, multiplies its difference from 100% by the gain to get the adjustment proportion. Gain is 0.5, EGO correction is 110%, then the VE adjustment will be 5%.

    There are a number of parameters that affect the operation of auto-tune. These are written into the custom.ini file:

    • allowAutoTune = on
    • corrector = egoCorrection
    • Vertex tolerance parameters
      • xRadius = 200 ; rpm
      • yRadius = 7 ; map
    • Tuning block parameters
      • xLimits = 1500, 4000 ; rpm
      • yLimits = 60, 90 ; map
      • zLimits = 10, 200 ; VE
    • Controller parameters
      • initialStartupInterval = 1.0 ; seconds
      • updateInterval = 1.0 ; seconds
      • proportionalGain = 0.5
      • lumpiness = 5 ; percent

    The radius (or vertex tolerance parameters) is how near to a vertex the operating conditions must be before the VE will be adjusted. For example, with the above settings, auto-tune will adjust a vertex if the operating point is within 200 RPM and 7 kPa of that vertex. If you increase the radius parameters, which would allow tuning farther from a vertex, then you may be changing the wrong vertex (typically four are involved at any given time, but auto-tune only changes the nearest one). The radius parameters try to minimize this error by only tuning when the nearest vertex has overwhelming influence.

    For the limits (or tuning block parameters), "X" is RPM. Y is normally MAP, TP or load. Z is the VE itself. The limit parameters box the tuning points, no changes will be made outside the box. The radius parameters dictate how close the operating point must be to the tuning point for auto-tune to operate, if the operating point falls outside this smaller box, then no action is taken. If you change the limits, then you don't change the accuracy or speed, just the region that is valid for tuning.

    Initial startup interval is the time in seconds between when the operating point approaches a tuning point and when the first adjustment is made.

    The update interval is the time between each subsequent adjustment.

    Note: If the interval parameters are made too short, the algorithm will become unstable and oscillate, since the EGO signal has some latency: you change the pulse width, which a cycle later causes the combustion mixture to change and then depending on the volume of pipe between the cylinder and the EGO sensor, there is some delay before the change is sensed. So you don't want to make these too short, you must allow enough time for the system to react and stabilize.

    Proportional gain is how much of the ego correction is used to adjust the VE value. If you set it to 1.0, and the ego correction indicates a 15% error, then the VE will be adjusted by 15%, while gain of 0.5 will adjust VE by 7.5%. I'd suggest keeping this at 0.5 or lower.

    Lumpiness is a parameter to limit how far a vertex's VE can be adjusted. The example below will keep the vertex that is being tuned within 5% of the extremes of the four surrounding vertices, under the assumption that the table should be somewhat smooth and will be 'rough tuned' to start. Note that the limits are transient, so if auto-tune changes vertex A by +5%, then moves to adjacent B, which also goes +5%, then the limit when we return to A will now be 5% above B.

    [AutoTune] 
       table = veTable1Map 
          lumpiness = 5 ; percent 
    

    There are two diagnostic messages to tell you what is going on with the auto-tune algorithm when it is turned on, but isn't doing any tuning. They are:

    • "Auto-tune: Tuning point outside window", which indicates that the operating point has gone outside the global x and y limits, so the no action will be taken. Likewise
    • "Auto-tune: Tuning point not near vertex", which indicates that the operating point is inside the global window, but it is not near enough a vertex (as defined by the "radius" parameters), and so no action will be taken. These messages are intended to help you figure out why the algorithm is not changing a vertex on the table, and allow you to modify the xLimits, yLimits, xRadius and yRadius parameters accordingly.

    Note that there are no menus to configure auto-tune in MegaTune (other than the EGO parameters). All the other data that MegaTune displays in dialogs for you to edit is stored somewhere inside your MegaSquirt; the tuning parameters for auto-tune are just MegaTune-specific data and really have nothing to do with MegaSquirt. This means that you need to edit the custom.ini file to make changes to the tuning algorithm's parameters. You may have to add to the custom.ini file:

    ;------------------------------------------------------------------------------- 
    ; Add your customizations here, they will be read at the end of the 
    ; standard megatune.ini processing and override any settings there. 
    ;------------------------------------------------------------------------------- 
    [AutoTune] 
    table = veTable1Map ; Should be the map3d_id of a TableEditor entry. 
    allowAutoTune = on 
    corrector = egoCorrection 
    
    ; Vertex tolerance parameters 
    xRadius = 200 ; RPM 
    yRadius = 7 ; MAP 
    
    ; Tuning block parameters 
    xLimits = 1500, 4000 ; RPM 
    yLimits = 60, 90 ; MAP 
    zLimits = 10, 200 ; VE 
    
    ; Controller parameters 
    initialStartupInterval = 1.0 ; seconds 
    updateInterval = 1.0 ; seconds 
    proportionalGain = 0.5 
    lumpiness = 5 ; percent
    

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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 MegaTune, 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. 
    	  

    Tools/Autotune

    Autotune is an algorithm built into recent releases of MegaTune that automatically tunes your VE table based on EGO feedback. It is similar to MSTweak3000, but operates in real-time, without a datalog, and on any variant of code and processor that uses MegaTune.

    The VE value inside MegaSquirt's RAM memory is modified and your engine feels the effect immediately, but it is not burned to flash and made 'permanent' until you click "Burn Table". If you do not burn the table, the changes will be lost the next time the power is cycled on MegaSquirt.

    With a narrow band sensor, you can use auto-tune with any algorithm and any sensor to tune the low-power part of the table, it will get you to stoich (or AFR targets) quite nicely, which will give you a starting point from which to extrapolate the high-power part.

    You don't need a dynomometer to get the high output regions of the VE table done, but you definitely should NOT use auto-tune with a narrow band sensor for that part of the table, you'll end up with broken or melted pistons. In order to use auto-tune for WOT tuning, you must be running a wide band lambda system (sensor and controller), with an appropriate EGO correction algorithm that allows you to set specific AFR targets (i.e., MSnS-Extra or MS-II). If one of these requirements is missing, then you must rely on seat-of-the-pants and experience.

    To enable autotune, select 'Tuning/VE Table1/Tools/Autotune'. An autotune status text indicator will appear in the message window in the lower right corner of MegaTune. Note that auto-tune updates the VE table in RAM, and requires that you click "Burn" to save the changed VE table permanently.

    Beware that if you go so rich that you start to see misfires, the lambda sensor will read the unburned mixture as dead lean (since unburned oxygen is present) and the closed loop algorithm will attempt to add fuel, which the auto-tune algorithm will detect and adjust the VE bin richer, thus making a bad situation worse. Use with caution, auto-tune will not perform magic!

    Typically, acceleration enrichment and decceleration enrichment happen while the engine RPMs are changing quite rapidly, and they usually turn off EGO correction at the same time, pretty much negating those two conditions.

    To start with, set the EGO step size (in MegaTune) to 1%, and set the authority down to ~10%, so that auto-tune doesn't do unstable jumps. The default auto-tune gain is 50%, so if you could jump a VE entry by as much as 5% in a single operation with the above numbers.

    The EGO control algorithms all turn off correction (i.e., set the correction factor to 100%) whenever AE, decel, warmup or any number of other enrichment types come active. The 100% EGO value in turn has the effect of turning off the auto-tune.

    The EGO correction step doesn't come into play at all, that's only internal to the EGO algorithm itself and dictates how rapidly it moves when correcting. The auto-tune step is determined by the current EGO correction (which is limited by the EGO controller authority), and the proportional gain, so only those two values really play a role in computing how big the auto-tune step will be. So, things proceed like this:

    1. The EGO algorithm uses whatever means necessary to come up with a number, this is limited to 100% +/- EGO authority with the familiar algorithms.
    2. The auto-tune algorithm uses the EGO correction value from 1, multiplies its difference from 100% by the gain to get the adjustment proportion. Gain is 0.5, EGO correction is 110%, then the VE adjustment will be 5%.

    There are a number of parameters that affect the operation of auto-tune. These are written into the custom.ini file:

    • allowAutoTune = on
    • corrector = egoCorrection
    • Vertex tolerance parameters
      • xRadius = 200 ; rpm
      • yRadius = 7 ; map
    • Tuning block parameters
      • xLimits = 1500, 4000 ; rpm
      • yLimits = 60, 90 ; map
      • zLimits = 10, 200 ; VE
    • Controller parameters
      • initialStartupInterval = 1.0 ; seconds
      • updateInterval = 1.0 ; seconds
      • proportionalGain = 0.5
      • lumpiness = 5 ; percent

    The radius (or vertex tolerance parameters) is how near to a vertex the operating conditions must be before the VE will be adjusted. For example, with the above settings, auto-tune will adjust a vertex if the operating point is within 200 RPM and 7 kPa of that vertex. If you increase the radius parameters, which would allow tuning farther from a vertex, then you may be changing the wrong vertex (typically four are involved at any given time, but auto-tune only changes the nearest one). The radius parameters try to minimize this error by only tuning when the nearest vertex has overwhelming influence.

    For the limits (or tuning block parameters), "X" is RPM. Y is normally MAP, TP or load. Z is the VE itself. The limit parameters box the tuning points, no changes will be made outside the box. The radius parameters dictate how close the operating point must be to the tuning point for auto-tune to operate, if the operating point falls outside this smaller box, then no action is taken. If you change the limits, then you don't change the accuracy or speed, just the region that is valid for tuning.

    Initial startup interval is the time in seconds between when the operating point approaches a tuning point and when the first adjustment is made.

    The update interval is the time between each subsequent adjustment.

    Proportional gain is how much of the ego correction is used to adjust the VE value. If you set it to 1.0, and the ego correction indicates a 15% error, then the VE will be adjusted by 15%, while gain of 0.5 will adjust VE by 7.5%. I'd suggest keeping this at 0.5 or lower.

    Lumpiness is a parameter to limit how far a vertex's VE can be adjusted. The example below will keep the vertex that is being tuned within 5% of the extremes of the four surrounding vertices, under the assumption that the table should be somewhat smooth and will be 'rough tuned' to start. Note that the limits are transient, so if auto-tune changes vertex A by +5%, then moves to adjacent B, which also goes +5%, then the limit when we return to A will now be 5% above B.

    [AutoTune] 
       table = veTable1Map 
          lumpiness = 5 ; percent 
    

    There are two diagnostic messages to tell you what is going on with the auto-tune algorithm when it is turned on, but isn't doing any tuning. They are:

    • "Auto-tune: Tuning point outside window", which indicates that the operating point has gone outside the global x and y limits, so the no action will be taken. Likewise
    • "Auto-tune: Tuning point not near vertex", which indicates that the operating point is inside the global window, but it is not near enough a vertex (as defined by the "radius" parameters), and so no action will be taken. These messages are intended to help you figure out why the algorithm is not changing a vertex on the table, and allow you to modify the xLimits, yLimits, xRadius and yRadius parameters accordingly.

    Note that there are no menus to configure auto-tune in MegaTune (other than the EGO parameters). All the other data that MegaTune displays in dialogs for you to edit is stored somewhere inside your MegaSquirt; the tuning parameters for auto-tune are just MegaTune-specific data and really have nothing to do with MegaSquirt. This means that you need to edit the custom.ini file to make changes to the tuning algorithm's parameters. You may have to add to the custom.ini file:

    ;------------------------------------------------------------------------------- 
    ; Add your customizations here, they will be read at the end of the 
    ; standard megatune.ini processing and override any settings there. 
    ;------------------------------------------------------------------------------- 
    [AutoTune] 
    table = veTable1Map ; Should be the map3d_id of a TableEditor entry. 
    allowAutoTune = on 
    corrector = egoCorrection 
    
    ; Vertex tolerance parameters 
    xRadius = 200 ; RPM 
    yRadius = 7 ; MAP 
    
    ; Tuning block parameters 
    xLimits = 1500, 4000 ; RPM 
    yLimits = 60, 90 ; MAP 
    zLimits = 10, 200 ; VE 
    
    ; Controller parameters 
    initialStartupInterval = 1.0 ; seconds 
    updateInterval = 1.0 ; seconds 
    proportionalGain = 0.5 
    lumpiness = 5 ; percent
    

    To make auto-tune work with earlier versions of MSnS-E (which require a INI file written before auto-tune was implemented) you'll need to use an old settings.ini and custom.ini, but cut the [AutoTune] section out of the new MT carMtCfg/custom.ini and paste it into your old one. Once you do this, you should scan your audit.log in the car1 directory to make sure that you are reading the old files an no new ones from the MT directories, as these might mess things up.

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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 MegaTune/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. 
    

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  • 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 MegaTune, 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. 
    

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  • 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 MegaTune, 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.

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• 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).

• 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. Setting custom temperature bins will cause issues with the correct display of the temperatures in the Warmup Wizard in MegaTune (TunerStudio handles this issue correctly). The graphical routine in MegaTune is only applicable for the default temperature bins, if you change them (as this user has), then the graphical bin values are displayed, but the bins actually correspond to the defaults, rather than the displayed values.

     You can still use the wizard, but you will have to reference the bar graph 'thermometer', rather than the values to the left of the pink WUE percent values (the arrow and pink WUE bin will point to the current warmup enrichment percentage, the current temperature is on the bar graph labeled 'Coolant').

     Some alternatives are to return to the default values for the temperature bins, or use TunerStudio.

  2. Note that the ASE and prime pulse values are grayed out in the warm-up wizard. 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.

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• 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 (v/sec in some older code versions) 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 the some v2.8 (& 2.6) INIs prior to Dec. 2007 have an error is in the TPSdot threshold setting. The error manifests itself as displaying the values as 1/10th the actual setting (so for example, 12.3 %/sec in MT would actually be 123 %/sec in the MS-II controller). You can tell if you have this error by looking at the TPSdot threshold in the accel enrichment wizard. If you have a decimal value displayed, then you are actually setting the value to 10x the shown value. You can either live with that by taking it into account, or put the appropriate updated INI in your project /mtCfg/ folder, and remaining it to megasquirt-II.ini (i.e., remove the numbers and periods at the end). The updated INI files are here:

  • 2.6: megasquirt-II.ini.2.6
  • 2.8: megasquirt-II.ini.2.8

  The change is to:

  tpsThresh = scalar, U08, 584, "%/sec", 1.00000, 0.00000, 0.00, 255, 0 ; * ( 1 byte)

  from:

  tpsThresh = scalar, U08, 584, "%/sec", 0.10000, 0.00000, 0.00, 25.5, 0 ; * ( 1 byte)

  (You can make this change yourself in the INI using notepad, if you prefer.)

  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.

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  X-Tau Tuning

  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.

  Other Tuning

  • 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.

  Communications

  MegaTune version 1.51 or later reads and saves the com port in a file named megatune.cfg. This file will be created in the same directory as the megatune.exe executable, if it does not exist.

  • Settings
    • Port The communications port number should correspond to the port to which the MS controller is attached. Usually you will select port 1 or 2, but some machines force you up to higher numbers (for instance, we have seen COM5 as the default on some IBM Thinkpad laptops). If you are using a USB/serial adapter, it may be as high as COM8 or COM9, or even higher. You can either look in the Control Panel under System/Device Manager, or simply try each COM port until you get a connection.
    • Timer Interval (ms) The timer interval dictates how frequently the runtime and tuning displays are updated. An interrupt is generated at the specified interval, and the real time data is pulled down from the MS controller. Use 100-200 ms to start; you can try to smaller values if your computer is fast enough (for example, 50 milliseconds works without problems on a P2 233 mHz laptop).
    • Serial Data Rate The data rate is hard coded into your MegaSquirt^® embedded code, use: 115200 for MegaSquirt-II. Other values will NOT work without re-coding and reprogramming and you will spend a lot of time trying to figure out what is wrong.
    • Verify ECU Communications Click this button to attempt communications with the MegaSquirt^® controller. Success will be reported if MegaTune is able to contact MegaSquirt.
      

  • Diagnostic Log:
    
  This creates a detailed communications log for troubleshooting. It is *NOT* the normal datalog of MS-II™ variables.
  • Mini-Terminal: This is an 'internal' version of hyperterminal for low level communications with MShift™ for troubleshooting, etc.

  Return to help index

  Tools

  • Calibrate TPS

    One of the first things you should do after installing MegaTune/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). It functions much like EasyTherm did for MegaSquirt-I.

    MegaTune 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, MegaTune 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 MegaTune 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 MegaTune 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 MegaTune reports in terms of both volts and AFR.

    MegaTune 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 MegaTune 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.

  • 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 MegaTune/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 MegaTune. (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 vapour form. If you use gasoline, it should be in a 'closed system' (One that does not allow vapours or liquid to escape). Be sure to have at least two fire extinguishers on hand, and keep them physically speareted 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 MegaTune- 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 MegaTune or 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. (Bruce and Al saw one for $8000 and all it had besides a controller were 8 burettes.)

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

  Return to help index

  Help

  • About Displays the program details:

  MegaTune Tuning Software by Eric Fahlgren {eric@wryday.com} Version 2.25 (release info is here) Originally derived from MegaSquirt® PC Configurator by Bruce Bowling and Al Grippo See http://www.megamanual.com/mtabcon.htm for full details.

• Topics

  Choose this for the Help topics available for MegaTune.

• 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^® towards UltraMegaSquirt.

  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 (Stephane Carrez has ported GCC to the HC12 processor so, although it doesn't use the full 9S12 instruction set, we are able to use his version to write code for the MS-II).

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

• Injector Characteristics
• Sensor Calibration