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Thread: 1:50,75 AFR-- no knock ??

  1. #1
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    Default 1:50,75 AFR-- no knock ??

    My first scan is very disappointing.C6 6Speed. 2 questions about it .
    I captured an OL Drive 1st gear 48%TP showing 50,75:1 for AFR at 0,872
    and 0.885 Volts.spark 28.5 KR is only 0.6. How can this be … no knocking this lean.
    This around 50 value appears also with lover rpm during acceIleration.
    I installed a catback before I had the Scan tool.
    So i rely on novice guessing. Is this possible by less backpressure only ?.
    Second finding, bank 1 and 2 long term fuel trims are simular distributed
    over almost all cells, but 5% apart . Looks like a different head.
    The ltft #s tend to be positive, the car runs lean, okay…. But it is very fast, maybe
    It could be fast already driving 200 Km/h an then accellerating.

    Any ideas …

    Greetings from Wiesbaden

  2. #2
    Joe (Moderator) joecar's Avatar
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    GV,

    Welcome to the forum...

    Which wideband oxygen sensor do you have...?

    Cheers
    Joe

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    Hi Joe ,

    your question is my answer. I don’t have anything other than the O2 sensors.
    That means it only makes sense to look for the voltage not for the calculated
    AFR-.. does it ?
    What do you think about the bank difference. Is 4-5 % less over all LTFT cell
    Within the normal rage.? It there a way to trim that anyway?

    Thanks

  4. #4
    Joe (Moderator) joecar's Avatar
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    GV,

    Oh, I see, you have the narrow band O2 sensors...
    So 50.75 is the commanded AFR....!?
    That is very strange.
    The LTFT1 and LTFT2 being 4-5% different may be due to an air leak on one bank, or something else.
    What are your LTFT's...?

    You can trim LTFT's by modifying the VE table B0101 and/or the IFR table B4001,
    but this trimming will not make LTFT1 and LTFT2 equal each other.

    You want the LTFT cells to approach 0%, and at WOT you want 920mV or a little higher.

    But... without a wideband sensor you cannot see what is the actual AFR.

    If you have a log, include a picture using this procedure (post #1 or #2): showthread.php?t=3064

    Cheers
    Joe

  5. #5
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    Hi Joe ,

    I still don’t know what to do about it, but I understand the data now.
    If I play the log watching the LTFT table gets filled I see a quick jump to
    the right side, high maps and the cells get filled downwards according
    the refs .When I shift a quick jump to the left with high values typically 13,3%
    for 15, 20 25 cells.
    So maybe this electronic throddle ( I do what I like ) pids rule here.
    The other bank then reads 10,9% or so. The difference looks worse then it is.
    And its’s in red , you know. That helps to be a little shocked.
    I will scan more specific, its fun.better than a videogame. :-))

    P.S. there is no VE table in V2, maybe this will be an upgrade

  6. #6
    Joe (Moderator) joecar's Avatar
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    Hi GV,

    So left bank reads 13.3% and right reads to 10.9%... that's a difference of 2.4%... that is small and is ok.

    Yes, it is much better than a video game...

    C6 Corvette may not have a VE table in the PCM... but I'm not sure of this.

    Regards
    Joe

  7. #7
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    You get these high AFR Value if you scan LS2 with the GM.AFR_1 Pid.
    a swap to GM.AFR_B_1 will make a almost fixed 14,7 and in open loop
    you see 11,5 to 13 which makes more sense although it is no replacement
    for a wideband.

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