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Thread: Short Term Fuel Trims Offline 0.0% at WOT

  1. #1
    Senior Tuner CCS86's Avatar
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    Short Term Fuel Trims Offline 0.0% at WOT

    Has anyone seen something like this?

    I see no signs of fueling system error, but as soon as it enters "power demand enrich" fuel source, the STFTs just flatline.
    Attached Files Attached Files

  2. #2
    Airflow - General - MAF Adaption - Enable

    [ECM] 2005 - MAF Adaption: Enable/Disable fuel trim updates during enrichment or enleanment.

    Any chance this is disabled and causing it?

  3. #3
    Senior Tuner CCS86's Avatar
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    That's a good thought, as the description sounds exactly like the behavior, and that setting is disabled in this tune. But, I also run that setting disabled on my personal car and have STFT's all the time (after the O2s warm up).

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    This usually occurs when you dont have enough o2 sensor delay so the widebands cant correct and sets a fault.

    Go double the delay in the area it occurs and see if its fixed.

  5. #5
    Senior Tuner CCS86's Avatar
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    Quote Originally Posted by decipha View Post
    This usually occurs when you dont have enough o2 sensor delay so the widebands cant correct and sets a fault.

    Go double the delay in the area it occurs and see if its fixed.


    That would also make sense. But this car is running stock headers and cats. The tune has nearly stock transport delay values (within about 2% at high load).

    I am running modified closed loop proportional/integral gains, so I can try reverting those. The values I'm using have run fine on a lot of similar cars, but maybe this particular strategy doesn't like them.

  6. #6
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    Bad O2 sensor or sensors. Transport delay is a property of the sensors responce rate not location.
    It gets compared to time constant to predict fouling and aging. Threshold of number of events for code may not be meet.
    I've seen the exact behavior just after clearing a sensor code.

    LOL just looked at your log 5 hours later.

    O2 sensors codes.PNG
    Last edited by murfie; 04-08-2021 at 04:03 AM.

  7. #7
    Senior Tuner CCS86's Avatar
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    Quote Originally Posted by murfie View Post
    Bad O2 sensor or sensors. Transport delay is a property of the sensors responce rate not location.
    It gets compared to time constant to predict fouling and aging. Threshold of number of events for code may not be meet.
    I've seen the exact behavior just after clearing a sensor code.

    LOL just looked at your log 5 hours later.

    O2 sensors codes.PNG



    Ha! Good eye!

    I completely missed those codes. You think some fresh O2s will likely clear that up?

    It is interesting that the codes are all related to a downstream sensor. I would think that if the widebands are online and working, it would keep using them to trim fuel. I thought the downstream sensors are only used to track catalyst performance and for FAOSC.
    Last edited by CCS86; 04-08-2021 at 10:49 AM.

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    is it not throwing a check engine light?

    that should have been obvious
    decipha @ EFIDynoTuning
    http://www.efidynotuning.com/

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    Unless the codes were set to no mil light which is a possibility?

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    Senior Tuner CCS86's Avatar
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    He says that no CEL was thrown. Maybe they were still pending?

    Either way, thanks for the help guys. I appreciate it!

    I'll report back whether no rear O2s fixed the issue.

  11. #11
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    Same here, bad o2s, when I see Fuel Source go into OL FMEM it was the o2 sensor. It can't read the fuel at that lambda, STFT are 0, no corrections, then the ECM cuts the injectors. Fuel Flow Rate went right to 0, let off the throttle and got right back on it.
    I change my o2s maybe once a year, I've had a lot of o2 issues before i fixed the issue. I know they can read adjust the fuel incorrectly and not throw an engine light. The bad o2 was barely making it, the good bank was keeping the adjustments going with no CEL I'd guess. These o2s seem to be in sync with each other.

  12. #12
    Was there something causing the car to eat sensors once a year?
    You mentioned until you fixed the issue

  13. #13
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    i have a 2016 GT PP car with only 4,800 miles on it and the LTFT stay at %0.
    No CEL at all but, I was thinking the same thing with mine. (bad O2's)

  14. #14
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    LTFT at 0% is either good, or you have a tune on it that has them disabled. Not likely an O2 issue.

  15. #15
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    You were right, not bad O2's, I did some more logging and it took about 25 minutes for the LTFT to start populating. I'm trying to build an airflow graph now. I know how to add the channel and make a graph but, I'm not getting the right parameter name in for it to build correctly. I'm searching for a thread on it, I'm sure someone has given proper instructions on it so I'll eventually find it. (Hopefully)