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Thread: Going Lean on WOT - is this a fuel pump issue?

  1. #1

    Going Lean on WOT - is this a fuel pump issue?

    My 1992 GMC with a swapped 5.3 from a 2002 Silverado is going really lean on WOT. I can see it go to 16.00 on my wideband and to 1.08 lambda on the scanner. The injector duty is also going way high. The truck has a 99 Silverado stock fuel pump.

    Please look at the log between frames 4950 - 5089. That section is pulling on the highway, WOT in 2nd and 3rd. The truck is a standard shift. If I need a different pump so be it, but I thought the stock 99 pump would handle this motor.

    The motor is all stock other than a CAI.
    Attached Files Attached Files
    2015 Corvette Convertible
    1992 GMC with 5.3 LM7
    Factory Five Roadster LS1 Tremec TKO

  2. #2
    Senior Tuner
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    Looks like fuel pump.

  3. #3
    Senior Tuner Russ K's Avatar
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    Check for plugged fuel filter, if ok then tape a fuel pressure gauge to the windshield and do a WOT run to redline. The fuel pressure shouldn't go less then 50 psi. I hope your not using the 1992 GMC fuel pump.

    Russ Kemp

  4. #4
    Thanks guys, I appreciate the confirmation. I'll get a gauge on it. I am using a new 1999 fuel pump. It doesn't seem to be keeping up at WOT.
    2015 Corvette Convertible
    1992 GMC with 5.3 LM7
    Factory Five Roadster LS1 Tremec TKO

  5. #5
    Potential Tuner
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    May 2013
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    I had this issue with my swap car last year. I mistakenly used hose clamps rather than fuel injection hose clamps. I bought the R10 submersible hose, however the incorrect clamp had caused fuel line deterioration and fuel pressure loss.

  6. #6
    Advanced Tuner
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    Is the tank 1/2 or below when this is happening? The fuel could be pulling away from the pickup. This has happened to a lot of guys with your swap.

  7. #7
    Advanced Tuner
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    Quote Originally Posted by Heavymetl View Post
    I had this issue with my swap car last year. I mistakenly used hose clamps rather than fuel injection hose clamps. I bought the R10 submersible hose, however the incorrect clamp had caused fuel line deterioration and fuel pressure loss.
    I had my hose come off the fuel pump using regular clamps. It sure sucks taking everything apart again. As they say you learn by your mistakes but if your lucky you will learn from others mistakes

  8. #8
    Senior Tuner
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    The way it flips from fat to lean during a WOT pull seems to
    say fueling, rather than anything like a spark blowout spoofing
    type problem. But your IPW readings are crazy - impossible,
    more like; you can't go past 100% duty nohow, no way, so
    what's the deal with that?

    Your O2 waveforms and how the STFTs creep say to me your
    NBO2s are untrustworthy. If you've gone and (say) tried to
    set up VE using a STFT based method, that could hurt you.

    Your MAF table, though, that's a flat-out mess. Pegged to
    max g/cyl about halfway up, on out. So if you are trying to
    use that airflow number, and adjusted fuel to it, the number
    will not change as RPM rises and this could account for a
    fading fuel delivered. I don't see any sign of this being a
    SD-only tune (MAF freq fail high, is a sane value).

  9. #9
    Senior Tuner
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    LTFT are active in the tune but not in the scanner. Im thinking as the o2 voltage falls off the LTFT are going way posititve and driving the ipw up.