2002 Sierra 4.3 high fuel trims

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by a.graham52, Aug 24, 2013.

  1. a.graham52

    a.graham52 Rockstar 100 Posts

    At cruise my LONG TERM fuel trims are +9,any other time (idle, wot) their around +3.

    Truck mods are:
    Trimmed butterfly (currently has stock I stalled)
    K&N filter (tested with stock paper)
    Flowmaster 50 exiting in front of The rear tire.
    Also has a mild tune (high fuel trims have been a problem before tune)

    Things I've done to try and correct the problem:

    Smoke tested intake and sealed all leaks except for the whisper of smoke coming from the throttle blade shaft.

    Redone all intake gaskets.

    Swapped modded parts for stock parts

    I've checked fuel pressure. 56psi KOEO, 53 at idle and 62 with ur foot in it. All seem to be within GM specs.

    Swapped out both MAF and MAP sensors for known good sensors.

    Removed PCV system from I take and plugged.

    If I unplug the MAF senso and run in "speed density" long term goes to negative 4! Major difference which says vac leak but I can't find one for the life of me.

    Anyone have any ideas where to go next?
  2. redvett

    redvett Rockstar 100 Posts

    You must have a crank case vent system or the engine will suffer. Your PCV will lower trims some if working right.
    Running too lean – High positive fuel corrections can be traced to MAF and O2 sensor faults, vacuum leaks from intake gaskets/hoses, unmetered air (intake snorkel leak), clogged or dirty fuel injectors, fuel delivery issues, and exhaust restrictions such as a clogged catalytic converter.
  3. a.graham52

    a.graham52 Rockstar 100 Posts

    I had reinstalled the PCV system yesterday when did intake gaskets. O2 sensor new 20k ago as we'll as the electric injectors (x engine). Fuel pressure seems to be within spec (for the x engine). Swapped out a the throttle body (Tps and iac included) and that made no difference. A clogged converter would cause rich fuel trims (lake of oxygen) and when I smoke tested the intake I did not find any smoke coming out of any place other then the throttle blade shaft.

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