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Thread: Quick guide to simultaneous VVE/MAF calibration for gen4+

  1. #201
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    Quote Originally Posted by hjtrbo View Post
    Great.

    Probably should have added instructions so I'll add them here.
    Find out what the IDs are that you are logging for these parameters:

    • Mass Airflow
    • STFT Bank 1
    • LTFT Bank 1 (Optional depending on tune config)
    • STFT Bank 2
    • LTFT Bank 2 (Optional depending on tune config)
    • Wideband Bank 1
    • Wideband Bank 2 (Optional)
    • EQ Ratio Cmd
    • Engine Speed
    • Intake Manifold Absolute Pressure
    • Volumetric Efficiency
    • Manifold Air Temp

    Head across to the spreadsheet and plug your IDs into the blue ID column.
    Copy smokeshows formula(s) back into your math parameter(s)

    The use of average is optional. I use an average of 200 for closed loop in all my logs as it seems to line up the GMVE data with the O2 sensor swings nicely. For open loop I do not use average. Play around with it to suit your own tastes.

  2. #202
    Quote Originally Posted by smokeshow View Post
    I still see a lot of people using the old method of disabling the MAF to calibrate their VVE on 4th generation LS stuff, that generally being E38 controllers and up. This isn't necessary anymore because you can log those GMVE values in real time with HP Tuners. All you need to do is use the proper math parameter(s) and filters to transform the data into the classic '% error' you're used to, which I will describe here. One thing to remember, as you always should when calibrating anything airflow related...it must be at steady state. So you should be using a method of your choosing to filter out transients, which I won't get into here. This method also assumes using short term fuel trims (LTFT disabled), so any open loop guys or calibration into the power-enriched range will have to incorporate fueling error from a wideband.

    The math:
    GMVE STFT % error = ((MAF_af)*(1+(STFT_avg)/100)-(GMVE_af))/(GMVE_af)*100

    Because steady state will always be looking at the MAF for airmass calculations, you must base your GMVE airflow error on the MAF airflow error. First, I normalize the STFT percentage so 0% becomes 1. A STFT of 5% would yield 1.05. Then multiply this by current MAF airflow to get an error corrected MAF airflow. From this value you subtract GMVE airflow to get a raw GMVE airflow error. Then, divide that error by the GMVE airflow to get your normalized VVE airflow error. Multiplying by 100 turns this back into % error to make pasting into the editor simpler.

    To break the GMVE airflow calculation down a bit...

    GMVE_af = (MAP*GMVE/IAT)*RPM/60*4

    Take MAP in MEGApascals (important) and multiple by the raw GMVE value from CAN and divide by the IAT in KELVIN (also important). This gives a single cylinder airmass. To get flow rate, multiply by RPM, divide by 60 to get revolutions per second, and multiply by 4 for the number of induction cycles in one revolution. If you have a 4 or 6 cylinder, multiply by 2 or 3, respectively.

    The full math parameter: GMVE STFT =
    (([16.71]*(1+(.01*[6.156]+.01*[8.156])/2)-[12.56]/60*4*[11.92]*[2312]/[2127.240])/([12.56]/60*4*[11.92]*[2312]/[2127.240]))*100

    Take this error data and plot it in your histograms and you would normally and save a bunch of time and disabling stuff in the calibration. As always, the more data points you get the better you filter out data noise.

    Screen capture of the parameter working...

    Attachment 101145

    Notice at the cursor point, the average STFT in the third graph is showing -4.4%, so a MAF airflow overestimation. However the GMVE airflow, being slightly lower is showing only 0.3% error, so it's right on for that operating point.

    Attachment 101147


    Update (06Nov2020): See the post below for information on improving this process using MAT versus IAT (if parameter is available)
    https://forum.hptuners.com/showthrea...l=1#post631001

    Just curiosity, why not log the actual corrected gmve value then copy and paste without the need to multiply by percent? That would also make it useful for building a gmve table from scratch using a calibrated maf. Or am I wrong?

  3. #203
    Advanced Tuner Cringer's Avatar
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    Quote Originally Posted by [email protected] View Post
    Just curiosity, why not log the actual corrected gmve value then copy and paste without the need to multiply by percent? That would also make it useful for building a gmve table from scratch using a calibrated maf. Or am I wrong?
    You can do that. However, this adds complexity and room for error when you convert the flow rate (grams/sec) from MAF into the values for the VVE table, which is cylinder airmass (in milligrams) multiplied by intake air temp (in Kelvin) divided by manifold pressure (in KPa). In my mathematical experiments, converting the flow rate into cylinder airmass never matches the cylinder airmass as determined by the ECM.

    I would direct you to a much easier way:
    read this:https://forum.hptuners.com/showthrea...-the-Same-Time
    and then: https://forum.hptuners.com/showthrea...287#post748287
    A standard approach will give you standard results.

    My Tuning Software:

    VVE Assistant [update for v1.5]
    MAF Assistant
    EOIT Assistant