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Thread: Initial fuel prime question

  1. #31
    Joe (Moderator) joecar's Avatar
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    ok, thanks.

  2. #32
    Lifetime Member Rich Z's Avatar
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    Anyone willing to take a stab at letting me know what might be causing that engine speed oscillation after I jolt the gas pedal after a cold start?

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    427 RHS block built by LME
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    It nearly died on the operating table, but I'm bringing her back.

  3. #33
    Joe (Moderator) joecar's Avatar
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    My stab/guess: it looks like it may be trying to use spark timing to adjust engine speed, but maybe spark timing is too high.

    ( now, the same comment could probably be applied to idle air )

    ( spark timing is related to idle air in the same manner as chicken/egg )

  4. #34
    Joe (Moderator) joecar's Avatar
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    Spark timing seems to overshoot to bring engine speed up;

    airmass seems to undershoot to bring engine speed back down.

  5. #35
    Lifetime Member Rich Z's Avatar
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    Quote Originally Posted by joecar View Post
    Spark timing seems to overshoot to bring engine speed up;

    airmass seems to undershoot to bring engine speed back down.
    So this issue appears to be timing related entirely? If I can stop the overshoot via timing, then the undershoot won't need to take place with airmass?

    CorvetteFlorida.com

    2002 Corvette Z06
    427 RHS block built by LME
    STS rear mounted twin turbos
    It nearly died on the operating table, but I'm bringing her back.

  6. #36
    Lifetime Member Rich Z's Avatar
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    Speaking of which.....

    Any ideas on why there is an apparent state change from idle when I blip the gas pedal? It acts like for 20 seconds it is accessing different tables after that event than it was using prior to the blip. So apparently the gas pedal blip is the trigger for that change.

    Is there any way in EFIlive to actually show (as per something similar to a debug routine in most programming languages) which tables are being accessed by the PCM in real time?

    CorvetteFlorida.com

    2002 Corvette Z06
    427 RHS block built by LME
    STS rear mounted twin turbos
    It nearly died on the operating table, but I'm bringing her back.

  7. #37
    Lifetime Member GMPX's Avatar
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    Quote Originally Posted by Rich Z View Post
    Is there any way in EFIlive to actually show (as per something similar to a debug routine in most programming languages) which tables are being accessed by the PCM in real time?
    Unfortunately that is technically impossible to convey down a super slow VPW communications bus.
    I no longer monitor the forum, please either post your question or create a support ticket.

  8. #38
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    Default Initial fuel prime question

    Quote Originally Posted by GMPX View Post
    Unfortunately that is technically impossible to convey down a super slow VPW communications bus.
    Is that a feature that could be worked into the scan tool viewer/runway highlighting... post processed? Assuming you selected the appropriate pids
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  9. #39
    Lifetime Member Rich Z's Avatar
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    Quote Originally Posted by Wheelz View Post
    Is that a feature that could be worked into the scan tool viewer/runway highlighting... post processed? Assuming you selected the appropriate pids
    Yeah, I would settle for that without the real time requirement. There seems to be several alternate tables that COULD be used based on values from sensors and settings in enabler tables that are difficult to predict just looking at one table at a time. For instance, just looking at the spark advance tables in my tune, there are SEVERAL possible tables that could be being used at any given time. When I am looking at a log graph, at any particular point, WHICH table, or tables, is actually being used to provide that data point? The graph only shows me the results. Without sitting down an drawing out a flow chart (even assuming I will find every single enabler switch possible), it's pretty darn tough figuring out which table is actually TELLING the PCM what spark advance value to use.

    Heck, just with B5916, which is the Base Spark Closed Throttle Threshold, the description says "If the throttle is below this value and vehicle speed is below threshold, then it is considered closed and the base spark tables will be used." Well, that's fine, but which spark table is being used when the throttle is ABOVE this value? Looks like it could be any of several based on ECT, IAT, knock sensors, fuel mixture correction, EGR spark correction, in gear or in park/neutral, etc., etc. And then we have multipliers to deal with as well.

    Heck, has anyone actually created a flow chart of this process to be able to MANUALLY trace what table is being used based on values that ARE discernible?

    CorvetteFlorida.com

    2002 Corvette Z06
    427 RHS block built by LME
    STS rear mounted twin turbos
    It nearly died on the operating table, but I'm bringing her back.

  10. #40
    Lifetime Member Rich Z's Avatar
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    Quote Originally Posted by joecar View Post
    Spark timing seems to overshoot to bring engine speed up;

    airmass seems to undershoot to bring engine speed back down.
    Actually I think you may be right on the money.

    I've been playing around with B4307 (Desired Airflow) and I've made a lot of headway. It looks to me that the values I had in this table were providing too much airflow, and when I destabilized idle by punching the throttle, airflow and spark advance were playing a tug of war trying to get the idle to stabilize again, taking 19 to 20 seconds before they were able to work together. I was also having a problem with high idle hanging when coming to a dead stop. Fiddling with this table seems to be getting all of the problems (idle surge, stalling, high rolling idle) straightened out, by reducing the amount of airflow. I've got the destabilization down to just 2 seconds, rolling idle runs around 900 or so rpm, and it no longer stalls when I punch the gas pedal right after cold start. I just need to work with it a bit more to try to find the sweet spot to get that idle destabilization down to zero seconds without messing up the other facets.

    Speaking of this B4307 table, can anyone tell me why the values in the Park/Neutral column are all zeroes? I checked a stock tune for a 2002 Z06 and that is what is there too. And there are other tables where there are only values in the In Gear column, but nothing but zeros in the Park/Neutral column. Is that the way it is supposed to be?

    CorvetteFlorida.com

    2002 Corvette Z06
    427 RHS block built by LME
    STS rear mounted twin turbos
    It nearly died on the operating table, but I'm bringing her back.

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