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Thread: VVT oscillation during cold start

  1. #21
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    Quote Originally Posted by McCloud View Post
    I did a compare with my stock file and it has the same setup as your JGC. I wish I could find documentation on the PCM that describes how the tables are coded/interact. It's is going to take alot of trial and error to figure these things out.
    That it is. Best way to see if VVT is disabled is logging exhaust cam position.

  2. #22
    Yeah I have it setup to log...

    Do you happen to know the answer to this one?
    https://forum.hptuners.com/showthrea...ighlight=Ratio

  3. #23
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    Isn't that just Pratio (unitless...kPa/kPa or psi/psi)?

  4. #24
    Quote Originally Posted by Homer View Post
    Isn't that just Pratio (unitless...kPa/kPa or psi/psi)?
    If you look at the numbers it looks like GPS i.e.. .20, .30, intead of 20, 30 etc..

  5. #25
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    Quote Originally Posted by McCloud View Post
    If you look at the numbers it looks like GPS i.e.. .20, .30, intead of 20, 30 etc..
    To me it resembles PE table except instead of FA the data in the cells is %. The ratio is unitless because it is a pressure/pressure...more specifically MAP/Baro. Therefore you can use it to multiply whatever unit of pressure you desire.
    pr table.JPG

  6. #26
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    VE is percent.

    It's Volumetric Efficiency. It's how efficiently the cylinders are filling.
    If in doubt, multiply everything by 1.1.

  7. #27
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    Quote Originally Posted by spoolboy View Post
    VE is percent.

    It's Volumetric Efficiency. It's how efficiently the cylinders are filling.
    He is asking about the column units, which is pressure ratio...unitless.
    question.JPG

  8. #28
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    Quote Originally Posted by Homer View Post
    He is asking about the column units, which is pressure ratio...unitless.
    question.JPG
    OH! Yeah, that's just a ratio - like a gear ratio - of the manifold pressure over atmospheric pressure.

    1 is whatever the baro happens to be at the moment and .8 would be 80% of baro.

    If you have a PR of 2.0, that would be 2 atmospheres, or about 14-15 psi of boost.
    If in doubt, multiply everything by 1.1.

  9. #29
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    Isn't Baro also measured as it is varies by weather and location? So you also need to know Baro to figure out true manifold pressure.

  10. #30
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    Quote Originally Posted by Homer View Post
    Isn't Baro also measured as it is varies by weather and location? So you also need to know Baro to figure out true manifold pressure.
    Baro isn't measured at all on most Chrysler stuff, unless it's one of the few applications with a baro sensor. The throttle flow model is used to model MAP in parallel with the measurement. This modeled 'CALC_MAP' is then filtered and used as an input to the throttle adaption function along with the measured MAP from the sensor. From there a number of adaptive variables are used to correct the modeled throttle phi ratio while the throttle adaptive integral and measured MAP are used to model part throttle baro. Then that calculated baro is used along with an arbitration between measured MAP and CALC_MAP to determine the p-ratio.

    If that sounds like a nasty mess, it's because it is. But it works.

  11. #31
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    Quote Originally Posted by smokeshow View Post
    Baro isn't measured at all on most Chrysler stuff, unless it's one of the few applications with a baro sensor. The throttle flow model is used to model MAP in parallel with the measurement. This modeled 'CALC_MAP' is then filtered and used as an input to the throttle adaption function along with the measured MAP from the sensor. From there a number of adaptive variables are used to correct the modeled throttle phi ratio while the throttle adaptive integral and measured MAP are used to model part throttle baro. Then that calculated baro is used along with an arbitration between measured MAP and CALC_MAP to determine the p-ratio.

    If that sounds like a nasty mess, it's because it is. But it works.
    So the Baro learn on GPEC2 and GPEC2A is not read from the MAP at KOEO or through a baro sensor (I thought there was a baro sensor on the GPEC2A engine controllers)?

    https://forum.hptuners.com/showthrea...ht=baro+sensor

  12. #32
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    Quote Originally Posted by smokeshow View Post
    Baro isn't measured at all on most Chrysler stuff, unless it's one of the few applications with a baro sensor. The throttle flow model is used to model MAP in parallel with the measurement. This modeled 'CALC_MAP' is then filtered and used as an input to the throttle adaption function along with the measured MAP from the sensor. From there a number of adaptive variables are used to correct the modeled throttle phi ratio while the throttle adaptive integral and measured MAP are used to model part throttle baro. Then that calculated baro is used along with an arbitration between measured MAP and CALC_MAP to determine the p-ratio.

    If that sounds like a nasty mess, it's because it is. But it works.
    OK, I kind-of follow that, but can you clarify phi for us non-calibration engineers?
    If in doubt, multiply everything by 1.1.

  13. #33
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    Quote Originally Posted by Homer View Post
    So the Baro learn on GPEC2 and GPEC2A is not read from the MAP at KOEO or through a baro sensor (I thought there was a baro sensor on the GPEC2A engine controllers)?

    https://forum.hptuners.com/showthrea...ht=baro+sensor
    The key on engine off provides the initial value for baro, but so long as baro adaption is enabled, everything that happens after the engine is running is a result of the learn function changing the baro value. Of course if there is a baro sensor present, this is a non-issue.

  14. #34
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    Well there is phee...phi...pho...and phum. Sorry could not resist.

  15. #35
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    Quote Originally Posted by spoolboy View Post
    OK, I kind-of follow that, but can you clarify phi for us non-calibration engineers?
    Lol, so it goes like this. Say you have a hole in a thin metal plate and you want to move air through the hole. You have to either build up pressure on one side or reduce pressure on the other side. You can calculate the mass flow rate through the hole if you know the effective area of the hole (absolute area * coefficient of discharge), velocity of the flow, and the density of the air on the high pressure side. Now, concerning the throttle body...due to physics, we know the velocity is equal to the speed of sound when the pressure ratio is below 0.528. We know the density of the air upstream of the throttle because of the modeled baro pressure and intake air temperature. And finally, we know the effective area of the throttle (as a function of flow) due to the bench calibration that the throttle goes through. Now the rules of compressible flow tend to fall apart a bit when the pressure ratio goes above 0.528. That's what the phi correction is for. Below that pressure ratio, the airflow becomes subsonic. So the phi ratio is a multiplier on that bench throttle flow calibration for pressure ratios above 0.528 to continue giving us a usable model of compressible flow through the throttle to continue estimating throttle mass flow.

    Now, phi is a variable itself and is updated based on models and measurements. Since we are measuring MAP and also have a running estimate of manifold pressure in the form of CALC_MAP, we can calculate an inferred flow discrepancy in the form of a set of throttle flow adaptives. Those adaptives are comprised of an adder, a multiplier, a proportional and an integral component. The phi variable is calculated with the throttle flow adaptive integral - phi is then used to calculate a new compressible flow factor to generate a corrected throttle mass flow when the air moving through it is subsonic, or P_Ratio > 0.528. Finally, the throttle adaptives all together are used to correct the values that come from the throttle body model.

    It's a nasty algorithm, isn't it? I won't go into any more detail now, but tl;dr...air goes through the throttle, we model both that flow and the manifold pressure; model the baro at low TPS, estimate/calculate baro at high TPS; compare the modeled MAP to measured MAP, calculate phi and throttle adaptives to correct for subsonic throttle flow and any offsets the throttle might have (manufacturing tolerances, throttle coking, etc). There's a lot more to this crazy algorithm but I'll stop there

  16. #36
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    Thank you for taking the time and typing all that out. I even mostly followed it!

    So basically we should not mess with phi. And some of the things we do - installing larger throttle bodies and playing with the ETC model tables - small & large range, and the ETC airflow table - probably have unintended consequences and maybe that's why so many folks have that neat oscillating throttle and runaway throttle.
    If in doubt, multiply everything by 1.1.

  17. #37
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    Quote Originally Posted by spoolboy View Post
    Thank you for taking the time and typing all that out. I even mostly followed it!

    So basically we should not mess with phi. And some of the things we do - installing larger throttle bodies and playing with the ETC model tables - small & large range, and the ETC airflow table - probably have unintended consequences and maybe that's why so many folks have that neat oscillating throttle and runaway throttle.
    Yeah that's exactly what happens. The software is almost recursive...lots of things are dependent on other things. So a small change makes big problems. Doing your due diligence to characterize the throttle as well as possible will go a long way.

  18. #38
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    So is phi a choked flow coefficient of some sort?

  19. #39
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    Quote Originally Posted by smokeshow View Post
    Yeah that's exactly what happens. The software is almost recursive...lots of things are dependent on other things. So a small change makes big problems. Doing your due diligence to characterize the throttle as well as possible will go a long way.
    Any tips on what to log and how to make adjustments for throttle body airflow? I would imagine a larger throttle body would be one scenario and positive pressure from boost would be another. Combine them and it's happy fun time!
    If in doubt, multiply everything by 1.1.

  20. #40
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    Quote Originally Posted by Homer View Post
    So is phi a choked flow coefficient of some sort?
    Phi is a correction on the multiplier that estimates subsonic, not-quite-choked flow.