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Thread: Confused by Fuel Trims

  1. #1
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    Confused by Fuel Trims

    I've been trying to adjust my fuel tables (Fuel Mass vs Inj PW and Inj PW vs Fuel Mass) by means of data-logging while driving around (not using a dyno)

    I will do start ups, easy driving, more aggressive driving in stages to dial in my fuel tables....

    Just when I think I have my fuel tables dialed in based on the data-logging and the applicable adjustments to the fuel tables, I will go for one last drive to verify all the changes are still showing good LT and ST fuel trims and then all of a sudden ALL of the logged data will show that every cell in the fueling tables is way to lean or rich (30%) and I will have to start over again.

    Each time I adjust the fuel tables I reset the adaptives, but there will be that odd time where the data log shows required fuel adjustments of 30% in every cell of the table.

    What am I not seeing? It's like there is a hidden LTFT that just decides to reset itself to zero and screw everything up.

    any help would be appreciated.

    2012 Challenger, 392 based 426 with 2.9 Whipple, 6.2 cam, 80# injectors
    Last edited by rich s; 06-02-2020 at 05:48 PM.

  2. #2
    Advanced Tuner
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    Do you have a datalog and corresponding tune of the issue?
    Are you logging other parameters that could effect the fueling such as ECT, IAT, MAT, PE etc?

  3. #3
    Tuner
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    Quote Originally Posted by HaasExp View Post
    Do you have a datalog and corresponding tune of the issue?
    Are you logging other parameters that could effect the fueling such as ECT, IAT, MAT, PE etc?
    unfortunately no. I will make an effort to save the log with a name I can identify.

  4. #4
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    and just to clarify..... it's not like i'm making adjustments then driving the car two days later and this occurs.... I'm logging, I pull into a parking lot, make the revisions, upload them to the car, drive some more within minutes of making the changes and boom.... 30% correction required....

  5. #5
    Potential Tuner
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    Jan 2020
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    better people to answer than I, but log IAT and make sure it's not getting heat soaked while setting in parking lot between tuning runs...
    2009 H2 6.2L Gen4 L9H w/ 6L80e AWD TSP VVT1, CNC Ported Heads

  6. #6
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    Quote Originally Posted by rich s View Post
    unfortunately no. I will make an effort to save the log with a name I can identify.
    Please also post the tune file.

  7. #7
    Advanced Tuner
    Join Date
    Feb 2016
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    Try an extra key on, key off, wait 10secs then fire it up after completing flashing the update.
    I have had this same thing happen at times...its like something messes up during flash procedure...strange but an extra key cycle usually sorts it.
    Worth a try.