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Thread: Fuel Pressure and Fuel Trims

  1. #1
    Advanced Tuner coachcrow56's Avatar
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    Dec 2004
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    Longview, Texas
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    Fuel Pressure and Fuel Trims

    Taking the advice of ZZPerformance, I removed my AEM fuel pressure regulator and re-installed my factory regulator. The engine now starts instantly ( took 3 or 4 seconds with the AEM regulator), but my fuel trims have spiked to -18. What has happened?

    The car is a 2000 GTP.
    3.0 Pulley/CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Intercooler/Headers/2500 Stall Converter/Autolite 104's/ZZP Fuel Rails/100 shot NOS/GMPP Sway Bars//I forgot the rest!!!

  2. #2
    Do you know what your AEM fuel pressure regulator was set at? The stock regulator is 48-55 so if it got tuned at 40psi you are now injecting too much fuel.

  3. #3
    Tuning Addict 5FDP's Avatar
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    May 2012
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    Is the factory regulator keeping it at the same pressure or allowing more fuel pressure?

    If it's more, I could see the higher negative trims because more pressure means more fuel will be going through the injector when it opens.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  4. #4
    Advanced Tuner coachcrow56's Avatar
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    AEM was set a 54 psi---supposedly!! Perhaps it was reading 54 at idle, but was actually lower! I have adjusted my LTFT's and now the car starts instantly, where before it took at least 2 to 3 seconds.
    Last edited by coachcrow56; 04-30-2019 at 07:25 AM.
    3.0 Pulley/CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Intercooler/Headers/2500 Stall Converter/Autolite 104's/ZZP Fuel Rails/100 shot NOS/GMPP Sway Bars//I forgot the rest!!!

  5. #5
    Advanced Tuner coachcrow56's Avatar
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    Dec 2004
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    Longview, Texas
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    Update to this post. The last few times that I have scanned the car, my fuel trims go lean, 6 to 7 to 8, under medium throttle at about 6500 mhz. I have no KR, but I know running extremely lean can damage the engine. Fuel pressure at idle is 48 psi. Didn't change after installing new pressure regulator. I think my fuel pump is failing to go into high speed mode. Replaced both of the fuel pump relays, no change. Attached a couple of scans. What do you think?
    Attached Files Attached Files
    3.0 Pulley/CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Intercooler/Headers/2500 Stall Converter/Autolite 104's/ZZP Fuel Rails/100 shot NOS/GMPP Sway Bars//I forgot the rest!!!

  6. #6
    Tuner in Training
    Join Date
    Apr 2015
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    14
    Can't look at your scan right now, but have u checked for any exhaust leaks pre O2 sensor? I had a leak at the crossover and it made me lean up till boost, then it was fine over 7000hz