Gio93z

Basically, I dropped the car off to have tuned and he said he couldn't finish the tune because my fuel pressure was dropping off at higher RPM's. I'm trying to pinpoint my problem. The vehicle is a 93 Camaro LT1 383ci.

I have a Granatelli 255lph fuel pump and an Aeromotive fuel pressure regulator and gauge. Also have Accel 30lb injectors.

When I had the car dyno-ed awhile back I had a lean condition while running this set up at an idle psi of 42. When the car was attempting to be tuned it was also at an idle psi of 42. The tuner told me that the fuel pressure was actually dropping as the RPM's went up esp under load.

I just bumper my idle fuel pressure to 50psi just to see what reaction I would get form the car and teh fuel pressure gauge. At idle it was staying at 50psi and under normal driving it stayed at 50 and went to about 52psi. Around 3/4 throttle, the fuel pressure blipped up to around 55psi and then ranged from 42psi to 48psi which obviously is a lower fuel pressure than at idle.

Any ideas anyone. I havn't checked voltage at the pump yet. All I have done so far was put a new fuel filter in, even though the one I took out was not clogged at all.


Thanks!

Injuneer

Are the pressures you are reporting for idle measured with or without the vacuum compensation line connected? Did you set the pressure at 50psi without the vacuum line connected? The fact that the pressure spikes when you go WOT would appear to indicate that you measured them with the vacuum line connected, and that when the vacuum disappears at WOT, the pressure is rising to 55psi. If its 55psi without the vacuum line connected, having the pressure drop to 42psi would indicate a weak fuel pump, a clogged filter or a faulty AFPR. Many people have had problems with the Aeromotive LT1 AFPR. Might want to check it out.

(NOTE to the person who is going to complain that I am knocking Aeromotive products, and that don't know what I am talking about - I am not knocking Aeromotive. They make some great products and are used on many high end perfromance vehicles. I am just noting that there appears to be a problem with the Aeromotive AFPR, and I am simply pointing that out based on the NUMEROUS posts on this site alone. Aeromotive admitted there was a bad batch, and offered free replacements - you are the one that came here and made the offer )

Gio93z

Basically I adjusted the fuel pressure with the car idleing and yes, with vacuum applied. I set it at 50 psi. While driving steady or just cruising the fuel pressure stays right near 50 psi. When I give it 3/4 pedal, if not more, and stay on it, the fuel pressure bumped upto about 52 - 53 and then as I hold the pedal it falls and ends up staying around 42 - 46 psi.

Injuneer

You should set your fuel pressure without the vacuum line connected. If the pressure falls off as much as 10psi fomr that pressure, there is a definite problem with your fuel system.

mrmint69

I would guess the pump. I have heard of problems with the fuel injectors your using. It probably doesn't matter but it could make a problem already there even worse.