Need help diagnosing fuel pressure drop...
Thread Starter
Instructor
Joined: Aug 2001
Posts: 123
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Need help diagnosing fuel pressure drop...
Over the last few weeks my GTA has been getting progressively slower. I've since found that i'm dumping fuel pressure under load. I set my pressure regulator at 50psi and it drops to around 40psi and the engine pings like crazy under severe load. By "severe load", I mean foot on the floor while doing 50mph. The trans downshifts to 3rd and the engine just pings and the FP drops. My timing is set at 6 degrees. I'm pretty confident the ping is caused by the lean condition and not spark knock. I just replaced the fuel filter, fuel pump(Walbro 255) and AFPR in hopes of fixing the problem. Upon replacing the AFPR the pressure was spiking to 50psi as it should but it only lasted for about 10 minutes and then it resumed it's hold at 40psi. Here's my list of modifications if that's relevant................
355 10.8:1 compression
LPE ported Edelbrock RPM heads
CompCams 1.6 ratio Pro Mag roller rockers
LPE "219" cam
SuperRam
Accel AFPR
LT-1 (24 lb) injectors
Accel 300+ ignition box
Ed Wright custom PROM (garbage)
Precision Industries Vigilante 2600rpm torque converter
I know it's not a 'Vette but this problem is killing me. I've had strange problems resolved by 'vetteforum members before and I hope you guys will be the cure one more time.
Thanks,
Paul
355 10.8:1 compression
LPE ported Edelbrock RPM heads
CompCams 1.6 ratio Pro Mag roller rockers
LPE "219" cam
SuperRam
Accel AFPR
LT-1 (24 lb) injectors
Accel 300+ ignition box
Ed Wright custom PROM (garbage)
Precision Industries Vigilante 2600rpm torque converter
I know it's not a 'Vette but this problem is killing me. I've had strange problems resolved by 'vetteforum members before and I hope you guys will be the cure one more time.
Thanks,
Paul
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Re: Need help diagnosing fuel pressure drop... (7xchampcar3)
Put a vacuum gauge in the line to the AFPR and assure that you have vacuum to hold the AFPR spring open under load.
Thread Starter
Instructor
Joined: Aug 2001
Posts: 123
Likes: 0
Re: Need help diagnosing fuel pressure drop... (65Z01)
Wouldn't it be stuck at 50psi if it wasn't getting enough vacuum? I was under the impression that it's the lack of vacuum at WOT that allows the pressure regulator to raise the fuel pressure.
Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
Re: Need help diagnosing fuel pressure drop... (7xchampcar3)
Wouldn't it be stuck at 50psi if it wasn't getting enough vacuum? I was under the impression that it's the lack of vacuum at WOT that allows the pressure regulator to raise the fuel pressure.
I would tape a fuel pressure guage on the windshield and take it for a ride at WOT to see what your delivery actually is .
[Modified by ittlfly, 7:15 AM 9/8/2002]
Thread Starter
Instructor
Joined: Aug 2001
Posts: 123
Likes: 0
Re: Need help diagnosing fuel pressure drop... (ittlfly)
I have been taping a pressure gauge to windshield. That's how I know the pressure won't go any higher than 40psi.
The injector o-rings are new and where seated properly.
The injector o-rings are new and where seated properly.
Team Owner
Joined: Apr 2000
Posts: 27,818
Likes: 8
From: CT
Re: Need help diagnosing fuel pressure drop... (7xchampcar3)
My pressure was dropping also(Taped a gauge to the windshield and tested) I traced it to a bad fuel pump. New pump in, problem solved.
Good luck
Good luck
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Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
Re: Need help diagnosing fuel pressure drop... (7xchampcar3)
Since you replaced the FP AFTER the problem started and it didn't cure the problem, it's got to be the FPR. (assuming the fuel filter and FP sock is OK).......Were you having the problem before or after you replaced the FPR? It really sounds like the regulator is craping out on you.
Thread Starter
Instructor
Joined: Aug 2001
Posts: 123
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Re: Need help diagnosing fuel pressure drop... (ittlfly)
Sorry, I replaced the AFPR after the problem started. I tested my old AFPR by pinching off the return line and priming the system. It held pressure while pinched but quickly bled off when released. That told me that my AFPR was bad. I replaced it and everything worked fine for about 10 minutes but then it started just sitting at 40psi and never risisng with RPM.
