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Fuel Pressure drop @ WOT?

This is a discussion on Fuel Pressure drop @ WOT? within the General Help forums, part of the LSx Technical Help Section category; I'm diagnosing a lean condition at WOT. Pretty much have it something in the fuel delivery. I checked the fuel ...

  1. #1
    Member 666ws6's Avatar
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    Fuel Pressure drop @ WOT?

    I'm diagnosing a lean condition at WOT. Pretty much have it something in the fuel delivery.

    I checked the fuel pressure, 58 steady, and then dips to 54-55 when I hit WOT. Pops right back to 58 when I let off the pedal. I assume that is a normal drop, right?

    So if pressure is good, does it mean the pump is perfectly fine? Or is there some other way to check?

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    Slow'er'Ass Mr. Luos's Avatar
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    Completely normal.

    Flow = loss of pressure.
    2008 Trailblazer SS
    Yank PTB3600, Kooks 1 7/8" LT's, 4" intake, E-fans, Magnaflow, Sonnax kit, tranny cooler, tune.
    Lowered, HID's, tinted.

    1999 Pontiac Trans Am WS.6 #1747 SOLD
    531.1 RWHP 481.3 FT/Pounds all motor.

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    Member 666ws6's Avatar
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    So if that pressure is normal, should I assume my pump/regulator is good and look elsewhere?

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    Slow'er'Ass Mr. Luos's Avatar
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    What mods?

    If you are at 54PSI with WOT...that is normal. Maybe just a touch low, but you are safe over 52-53.

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    Member 666ws6's Avatar
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    My mods

    228R cam, pulleys, LT headers, LS6 intake, GMAF, lid, SY3500 converter w/ shift kit, 3.90 gears, cutout, borla...

    I've eliminated the GMAF (problem remains even in SD mode) and I think the fuel pump/regulator is fine do to that pressure test.

    Even when we forced the air/fuel ratio to 10.1 through EFILive, it still logged data at 14.7/1 at heavy throttle.

  6. #6
    Slow'er'Ass Mr. Luos's Avatar
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    What tuning changes did you make when you ran SD?

    Got a stuck injector?

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    old timer blue02Z's Avatar
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    Mr. Luos that is what i was thinking. maybe its stuck, but that would most likely set a P030X code. how lean are you at WOT

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    Member 666ws6's Avatar
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    I don't have the full extend of all the details, and I'm away from my car until the weekend. Wouldn't a stuck injector be an easy find and wouldn't I feel it in performance?

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    Member 666ws6's Avatar
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    Lean problem found!

    I finally found my lean problem at heavy throttle.

    I had an A/F gauge as a place holder tapped into the wires just before the PCM. When I removed that, I still had the lean condition, but when I went to SD (disconnected MAF) I now showed a little rich at WOT. So I got a new stock MAF and left the A/F gauge out... and all is good. A little rich at WOT, but my tuner will tweak that.

    That stupid A/F gauge was masking the ture problem because before when I drove in SD with the gauge still wired in, I still was lean.

    Feels so good to have it fixed!

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    old timer blue02Z's Avatar
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    are you running a K&N filter by any chance?

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    Member 666ws6's Avatar
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    K&N has been in for 50k miles or so. But the new MAF fixed my issue. I had a GMAF, instead of the stocker. Living proof that staying with the stock MAF is a wise choice.

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    old timer blue02Z's Avatar
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    fo sho. my slp maf was messing up a few weeks ago so i swapped my stocker in and runs great now. kn is excellent at getting oil on your maf wires and f'n it all up. glad to hear its running good now

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