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Thread: VE Airflow

  1. #1
    Senior Tuner LSxpwrdZ's Avatar
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    VE Airflow

    This is nothing new to me but thought I'd ask why this happens the way it does. When dialing in a MAF table on any E38/67 with the VVE disabled by setting dynamic airflow to less than an rpm point I will be tuning in, the VE airflow works as it should up until 4K rpm. If the VE is off it'll read quite different airflow values as compared to the raw MAF airflow or the dynamic airflow. However even though it may be completely off when 4K rpm comes around it instantly tracks the current MAF and dynamic airflows above 4k rpm. The way I understand that PID is that its supposed to track the VE independant of what mode the ECM is currently running in. Is there still a 4k rpm setpoint in the calibration that would cause this?
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  2. #2
    Senior Tuner DSteck's Avatar
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    I don't understand your question. I've never had them match unless VE is correct. However, I never use the airflow values and instead default to GM Volumetric Efficiency and my own calculated GMVE.

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  3. #3
    Senior Tuner LSxpwrdZ's Avatar
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    My question is why does the VE Airflow PID stop reporting the actual VE Airflow at 4000rpm when it is actually disabled at a completely different RPM?

    Maybe the VE Airflow is limited to 4000rpm in that particular PID...
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  4. #4
    Senior Tuner SultanHassanMasTuning's Avatar
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    lets say you kept VE working up to 4k like the factory, when i disabled it i need to work on my fuel trims again. which tell me its disabled
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  5. #5
    Advanced Tuner Bluecat's Avatar
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    I dont log the "VE airflow" pid, so I don't have experience with what your seeing. I do log the "Dynamic Airflow" pid, which is the airflow value that shows the final airflow value used for the fuel calc, that being SD or MAF derived. I also log "GM Volumetric Efficiency" which is the strait up GMVE from the VE table or VVE. I know for a fact that it doesn't revert to any maf or blended value at any time or rpm. If you need a VE derived airflow while running in MAF mode, use the "GM Volumetric Efficiency" pid and create a custom pid from it to back into the VE airflow.

    I do the same thing in reverse. I have a custom "Dynamic GMVE" that derives from the "Dynamic Airflow" pid and spits out the GMVE numbers based off of it. I can use it build a VE or VVE off of the current MAF tune. And I use the "Dynamic Airflow" pid to build a MAF table from the current SD tune.

  6. #6
    Senior Tuner DSteck's Avatar
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    Post the file you're logging.

    I also never use VE Airflow, and instead use Dynamic Airflow and GM Volumetric Efficiency to log. I back calculate off of my wideband for GMVE though as opposed to using Dynamic Airflow. I could have a car in pure MAF mode with a total junk MAF cal, and still directly calibrate the GMVE model. Actually just used it all last night... Had a cammed C6 that was way off on the MAF, and VE wasn't even close. One 20 minute data log was sufficient to calibrate both. Reflashed after one log, rechecked, and was +/-2% error or better everywhere (except hard transients or DFCO, obviously).

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    Dave, can your model be used on gen 3 cars to populate the VE table?

    I want to dig further to figure it out, but I don't want to waste my time if you can't do it on a gen3.

  8. #8
    Senior Tuner DSteck's Avatar
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    Quote Originally Posted by BigMike42 View Post
    Dave, can your model be used on gen 3 cars to populate the VE table?

    I want to dig further to figure it out, but I don't want to waste my time if you can't do it on a gen3.
    I don't think Gen III supports the required PIDs, but pulse width is displayed with the offsets and short pulse adder factored in which throws it off.

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  9. #9
    Senior Tuner LSxpwrdZ's Avatar
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    Yeah that is the way I was using the VE Airflow to back calculate based off dynamic airflow and wideband data to generate a calibrated VVE. I noticed once I got above 4000rpm even though the dynamic disable was 200rpm it jumped from being 20-30% off to dead nuts on my dynamic airflow (which was at the time basically filtered MAF). I don't think I have any particular tune files with logs currently to post up as I normally just put the cars in full SD and calibrated it the old school way with lambda error but the full MAF and back calculate the VVE is so much faster especially with wideband data to dial it in even closer.

    I'll tinker around in my custom PID setup and change out VE Airflow for GMVE and see where that gets me.
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  10. #10
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    Quote Originally Posted by LSxpwrdZ View Post
    Yeah that is the way I was using the VE Airflow to back calculate based off dynamic airflow and wideband data to generate a calibrated VVE. I noticed once I got above 4000rpm even though the dynamic disable was 200rpm it jumped from being 20-30% off to dead nuts on my dynamic airflow (which was at the time basically filtered MAF). I don't think I have any particular tune files with logs currently to post up as I normally just put the cars in full SD and calibrated it the old school way with lambda error but the full MAF and back calculate the VVE is so much faster especially with wideband data to dial it in even closer.

    I'll tinker around in my custom PID setup and change out VE Airflow for GMVE and see where that gets me.
    You can do MAF and VE at the same time...calculate MAF airmass from the wideband data you have, and then the conversion to GMVE is just taking that value at any given time (with filters to avoid fast transients) multiplying it by airmass temp (in Kelvin...log manifold air temp) and the number of cylinders, then dividing by MAP pressure.
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  11. #11
    Senior Tuner LSxpwrdZ's Avatar
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    Quote Originally Posted by MikeOD View Post
    You can do MAF and VE at the same time...calculate MAF airmass from the wideband data you have, and then the conversion to GMVE is just taking that value at any given time (with filters to avoid fast transients) multiplying it by airmass temp (in Kelvin...log manifold air temp) and the number of cylinders, then dividing by MAP pressure.
    Yep thats what I was going to do. It's a bit more involved setting it up but works. The VE Airflow was simple because all you needed to do is calculate the difference between the MAF and VE Airflow while using lambda error to correct any MAF discrepancies and one log would have the VVE perfect. This obviously being done rpm column at a time on an eddy current dyno.
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  12. #12
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    My formula is a little off actually, but I'm working on it and I'm close. I should have ve and maf nailed down soon then I'll share.

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    let me get this right, so let's say i have MAF dialed in (maf only tune). there's a way to use the correct information that i have in the MAF to setup the SD part of the tune?

    if so, i'd love to do that and set it back to the 4000 rpm SD/MAF tune. I'm just a little confused on all this talk you fellers are saying right now.

  14. #14
    Senior Tuner DSteck's Avatar
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    That's exactly what I do, except it doesn't rely on a properly calibrated MAF.

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    Quote Originally Posted by 1quicktpi View Post
    let me get this right, so let's say i have MAF dialed in (maf only tune). there's a way to use the correct information that i have in the MAF to setup the SD part of the tune?

    if so, i'd love to do that and set it back to the 4000 rpm SD/MAF tune. I'm just a little confused on all this talk you fellers are saying right now.
    Almost...you can actually calibrate both the MAF and VE using wideband data when neither one is calibrated to begin with...so long as the vehicle will run, and the AFR is somewhere in the range your wideband can measure. It's just easier to me to think of the equation to determine airmass directly, and then add a little more to that equation to derive GMVE. I'm still verifying that I did it right, once I do I'll be happy to share my math for everyone.

    Quote Originally Posted by DSteck View Post
    That's exactly what I do, except it doesn't rely on a properly calibrated MAF.
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    Ah gotcha, Thanks guys. My truck will run with the stock MAF tables within my wideband range, so i can revert it back to stock and do as your saying, if need be. would this still require me to run the bluecat software for the VE or could i do it purely wideband?

    I do apologize if I'm way behind on this, but I do appreciate all the help

    I'll be keeping an eye on this thread.

  17. #17
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    Quote Originally Posted by 1quicktpi View Post
    Ah gotcha, Thanks guys. My truck will run with the stock MAF tables within my wideband range, so i can revert it back to stock and do as your saying, if need be. would this still require me to run the bluecat software for the VE or could i do it purely wideband?

    I do apologize if I'm way behind on this, but I do appreciate all the help

    I'll be keeping an eye on this thread.
    If you're going to use the GM operating system, then the software from Bluecat will still be necessary to convert the GMVE table you build into the equation coefficients for the PCM, unless you know how to do it in Excel. If you use the HPTuners enhanced OS then you don't need to do that.
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    Alright thanks, guess i'm gonna have to quit being lazy and use my bluecat stuff. lol

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    How is this accomplished?

  20. #20
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    Quote Originally Posted by azreeal View Post
    How is this accomplished?
    Do some searching around on this forum. There's a handful of helpful threads with scanner math functions listed out. I don't have the links saved on the PC I'm currently on, though if you search GMVE from MAF you can probably come across them.
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