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Thread: Fuel Pump Problem?

  1. #1
    Advanced Tuner coachcrow56's Avatar
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    Fuel Pump Problem?

    After 105,000 miles, I have my first real problem with my 2000 GTP. When I punch it, the car falls flat on its face at 4000 rpm---scanner shows that it goes crazy lean. Fuel Filter is new, and about 500 miles ago I installed a Caspar Fuel Pump rewire kit. When I attach a fuel pressure gauge and cycle the key on and off 3 times, I have 40 psi with key on, then key off and it slowly drops---after 15 minutes it is down to 32.8 psi. This car has 2 fuel pump micro relays--14 and 15 (F/PMP SPD CONT).

    When I crank car, I have 42 psi at idle. Disconnect vacuum from regulator, I have 52. Turn off engine, gauge drops immediately to 33 psi. After 15 minutes, it is down to 20 psi.

    Could I have a bad high speed pump relay, trash in the tank, etc. ???? Any thoughts or suggestions are welcome.
    Last edited by coachcrow56; 03-08-2014 at 12:06 PM.
    2.8/3.0/3.2 Pulley/ZZP CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Stage 2 Intercooler/TOG Headers/Triple Edge Performance Stage 3 Transmission/3.29 Ratio/NGK TR6ix IRIDIUM .40 GAP/ZZP Fuel Rails/ZEX 100 shot NOS/GMPP Sway Bars/KYB Adjustable Struts/Power Stop Performance Pads/Rotors

  2. #2
    Senior Tuner Russ K's Avatar
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    It's normal for the fuel pressure to drop off after 15 min. Tape the pressure gauge to the windshield and do a WOT to redline to test the pump.

    Russ Kemp

  3. #3
    Advanced Tuner coachcrow56's Avatar
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    Russ---thanks for your help. I got a Fuel Pressure gauge from my son's shop with a long cord, did a WOT run----above 4000 rpm the AFR's went lean into the 13's as fuel pressure dropped below 40 psi.

    I purchased an ACDelco fuel pump for $340. I installed it today, and fuel pressures went up to 46 with key on and 48 at idle. I used your MAF tuning method to tune my AFR's, and now it locks at 11.5 at WOT. Car runs better than ever.

    I had been battling fluctuating fuel trims for several months--it would go lean at one red light, and then go extremely rich at the next red light. I never knew that fuel pressure had so much effect on tuning, but thanks to you, I have learned something new.
    Last edited by coachcrow56; 03-09-2014 at 06:31 PM.
    2.8/3.0/3.2 Pulley/ZZP CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Stage 2 Intercooler/TOG Headers/Triple Edge Performance Stage 3 Transmission/3.29 Ratio/NGK TR6ix IRIDIUM .40 GAP/ZZP Fuel Rails/ZEX 100 shot NOS/GMPP Sway Bars/KYB Adjustable Struts/Power Stop Performance Pads/Rotors

  4. #4
    Tuning Addict 5FDP's Avatar
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    Holy crap, 340 for a fuel pump..

    You coulda bought an upgraded pump for cheaper, but atleast the car runs alright.
    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.

  5. #5
    Advanced Tuner coachcrow56's Avatar
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    Fuel Pump Resistor

    Car has run great until this week. When cranked cold it dies. Takes 2 or 3 tries to get it to keep running. Fuel pressure at idle has dropped to 40 psi.

    When I turn on ignition key, you can hear pump kick on and gauge reads 52 psi, and immediately begins a rapid drop with key on down to almost 0. Any ideas??
    2.8/3.0/3.2 Pulley/ZZP CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Stage 2 Intercooler/TOG Headers/Triple Edge Performance Stage 3 Transmission/3.29 Ratio/NGK TR6ix IRIDIUM .40 GAP/ZZP Fuel Rails/ZEX 100 shot NOS/GMPP Sway Bars/KYB Adjustable Struts/Power Stop Performance Pads/Rotors

  6. #6
    Advanced Tuner coachcrow56's Avatar
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    Quote Originally Posted by coachcrow56 View Post
    Car has run great until this week. When cranked cold it dies. Takes 2 or 3 tries to get it to keep running. Fuel pressure at idle has dropped to 40 psi.

    When I turn on ignition key, you can hear pump kick on and gauge reads 52 psi, and immediately begins a rapid drop with key on down to almost 0. Any ideas??
    I have come to the conclusion that it is a bad check valve in the fuel pump---any comments?
    2.8/3.0/3.2 Pulley/ZZP CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Stage 2 Intercooler/TOG Headers/Triple Edge Performance Stage 3 Transmission/3.29 Ratio/NGK TR6ix IRIDIUM .40 GAP/ZZP Fuel Rails/ZEX 100 shot NOS/GMPP Sway Bars/KYB Adjustable Struts/Power Stop Performance Pads/Rotors

  7. #7
    Tuning Addict 5FDP's Avatar
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    Or the regulator on the fuel rail has failed.
    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.

  8. #8
    Advanced Tuner coachcrow56's Avatar
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    I have an AEM Fuel Pressure Regulator (AVM-25-302BK). I pulled the vacuum hose off while the car is running, readings on the gauge change, and there is no fuel in the vacuum line. So I think its good.
    2.8/3.0/3.2 Pulley/ZZP CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Stage 2 Intercooler/TOG Headers/Triple Edge Performance Stage 3 Transmission/3.29 Ratio/NGK TR6ix IRIDIUM .40 GAP/ZZP Fuel Rails/ZEX 100 shot NOS/GMPP Sway Bars/KYB Adjustable Struts/Power Stop Performance Pads/Rotors

  9. #9
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    Fuel Filter??

  10. #10
    Advanced Tuner coachcrow56's Avatar
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    Changed 1000 miles back.
    2.8/3.0/3.2 Pulley/ZZP CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Stage 2 Intercooler/TOG Headers/Triple Edge Performance Stage 3 Transmission/3.29 Ratio/NGK TR6ix IRIDIUM .40 GAP/ZZP Fuel Rails/ZEX 100 shot NOS/GMPP Sway Bars/KYB Adjustable Struts/Power Stop Performance Pads/Rotors

  11. #11
    Tuner in Training
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    You'll have to check the relays and grounds next.

  12. #12
    Advanced Tuner coachcrow56's Avatar
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    Relays and grounds have all been checked. Back when I installed new pump and AEM regulator, I also installed Casper's GTP Fuel Pump Hotwire Kit to boost voltage. All electronics are working correctly.
    2.8/3.0/3.2 Pulley/ZZP CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Stage 2 Intercooler/TOG Headers/Triple Edge Performance Stage 3 Transmission/3.29 Ratio/NGK TR6ix IRIDIUM .40 GAP/ZZP Fuel Rails/ZEX 100 shot NOS/GMPP Sway Bars/KYB Adjustable Struts/Power Stop Performance Pads/Rotors

  13. #13
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    Can You post a scan a drive?

  14. #14
    Advanced Tuner coachcrow56's Avatar
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    Sometimes it helps to call people who are smarter than me----LOL!!!. I called AEM, and the tech said it was normal for the fuel pressure to drop when the key is on---not started. I adjusted my tune (idle), readjusted the AEM regulator, and now all is good. Live and Learn!!!
    2.8/3.0/3.2 Pulley/ZZP CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Stage 2 Intercooler/TOG Headers/Triple Edge Performance Stage 3 Transmission/3.29 Ratio/NGK TR6ix IRIDIUM .40 GAP/ZZP Fuel Rails/ZEX 100 shot NOS/GMPP Sway Bars/KYB Adjustable Struts/Power Stop Performance Pads/Rotors