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Thread: Idle fueling open loop

  1. #1
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    Idle fueling open loop

    Looking for some help with a rich condition at idle.

    I have a sbc with a 230/236 duration 110lsa cam, and long tube headers. Im having a hard time getting my engine to idle at the commanded afr in closed loop. Im able to get the fueling right in open loop, but as soon as i put it back in CL the LTFT brings it back rich. Commanding 14.52afr and seeing 13.5 at idle. Fueling at part throttle and wot is good.
    Stock injectors, stock intake, P01 GM Gen 3
    Last edited by motoXXX; 10-03-2022 at 10:11 AM. Reason: Open loop Closed loop

  2. #2
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    Any ideas about what i should look at? Or where I should start?

  3. #3
    Im guessing you may have meant that you can get it to idle at your desired fuel mixture in OPEN loop, but then the fuel trims bring it back rich in CLOSED loop?
    What are your narrowband O2 sensors reporting at CL idle when your WB says rich - are they agreeing with your WB and saying rich as well, or are they indicating stoich mixture? (which they should if theyre driving fuel trims that direction). Is the voltage swing of the sensors relatively quick and consistent?
    The camshaft overlap (EGR effect) may be throwing off the perceived fuel mixture at idle, and the long tube headers may be fooling with the transient time from combustion to reaching the sensors. Maybe poke around those two potential phenomena

  4. #4
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    Quote Originally Posted by CaudleDynamicsLLC View Post
    Im guessing you may have meant that you can get it to idle at your desired fuel mixture in OPEN loop, but then the fuel trims bring it back rich in CLOSED loop?
    What are your narrowband O2 sensors reporting at CL idle when your WB says rich - are they agreeing with your WB and saying rich as well, or are they indicating stoich mixture? (which they should if theyre driving fuel trims that direction). Is the voltage swing of the sensors relatively quick and consistent?
    The camshaft overlap (EGR effect) may be throwing off the perceived fuel mixture at idle, and the long tube headers may be fooling with the transient time from combustion to reaching the sensors. Maybe poke around those two potential phenomena
    Yes you are correct. I had open loop/closed loop backwards in my initial post. Idle mixture is fine in OPEN loop, but goes rich during CLOSED loop according to my wideband. The O2 oscillation at idle seems erratic and inconsistent. Once O2 oscillation becomes consistent at partial throttle, fuel mixture becomes correct in CL.
    What parameters should i look at to adjust the transient time you have mentioned? Or is there a way to turn off CL correction only at idle?

    Thanks!

  5. #5
    Its been a while since I was really in-depth with a GenIII PCM and at the time was mostly using a different tuning package. Someone else might be able to point right to the exact tables, but I can take a look if you have a tune file (some OS's and applications have different tables available than others).