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Thread: positive LTFT on Idle

  1. 03-16-2018 #1
    Holdensbizz
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    positive LTFT on Idle

    Have a quick question and wondering on some thoughts. Just swapped a 5.3L in a 91 Jeep for a guy, got it up and running but I have super high fuel trims when idling. (like +25). When I unplug the MAF the LTFTs come to a normal level +/- 5.
    Swaped out the maf and same thing. he didn't want to put new 02 sensors in so i reused the old 02 sensors. Is the MAF so far out that its reading that high on the 02s or would/could the 02s be bad? OR could the MAF be calibrated? OR just change the injector flow rate?
    Any thoughts would be helpful.
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  2. 03-16-2018 #2
    5FDP
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    Is everything stock, down to the intake manifolds and manifolds?

    Have to double checked for vacuum leaks yet?

    My bet is that something is changed from stock, incorrect fuel pressure (must be 58psi) or you have a bad leak after the MAF and before the o2 sensors.


    On a side note here, NEVER change the injector flow rate to compensate for a real problem. The IFR should only be changed when the injectors are changed to a different size.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.
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  3. 03-17-2018 #3
    Holdensbizz
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    I was not a fan of changing the IFR, a couple people I have worked with do that to bring in the LTFTs.
    Stock 5.3L, looks like new intake manifold gaskets, stock injectors, stock manifold and throttle body.
    Sanderson headers, CCLS1c I think, the air intake is a fiber "cold" filter, rubber 90* and 45* and a piece of aluminum all 4''
    checked for vacuum leaks at first, couldn't hear or feel any, did the old brake cleaner trick carefully as well.
    Checking the PSI now...
    Thanks for the info and help.
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  4. 03-17-2018 #4
    Holdensbizz
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    PSI is holding steady at 58
    Copy.hpl
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  5. 03-17-2018 #5
    5FDP
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    How high in elevation are you?

    The KOEO map KPA readings are in the mid 80's, that would be wrong if you are closer to sea level.

    Post the tune if you have it.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.
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  6. 03-17-2018 #6
    Holdensbizz
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    Copy.hpt
    4500 feet elevation
    looked all over for a broken manifold, or something couldn't find anything showing an air leak.
    Also popped off all the injectors to see if one was stuck of something strange, all opened fine.
    Fuel pressure dropped after the engine was shut off, regulator on the rail seemed to work fine.
    Thank you again for your help
    Last edited by Holdensbizz; 03-17-2018 at 08:10 PM.
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  7. 03-18-2018 #7
    Holdensbizz
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    So Just found out from the owner that the computer is from a different vehicle, then all the sensors.
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