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. Also, the needle on my FP gauge dances around at idle and in OD and only becomes steady under load. It bounces from 35psi to 60psi. 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. A reliable source mentioned that the sock on the pump may have collapsed. How can I narrow it down to injectors, regulator, or pump? Here's my mods 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

Thanks,
Paul

 

I forgot to add that my fuel pressure drops to around 15psi very quickly after I shut the car off or when I just cycle the pump before starting.

 

I just messed with it some more and the pressure is dropping to 0 within 20 seconds after I shut it off or cycle the pump.

 

Well first of all clamp the return lines and make sure no fuel is leaking out of the pressure regulator, then prime the pump and see if the pressure falls off. If so, remove the plenum and pull the fuel rail out with the injectors attached, then prime the pump. You will be able to visibly see if any injectors are leaking.

Make sure your fuel pressure tester is tight on the schraeder valve, that could cause fuel pressure to appear to bleed off quickly if not attached properly.

By the way, remember how I pmed you about how my car wouldn't get fuel when warm? Well the problem has gone away on it's own, I have no idea what was/is wrong. But I'll tell you one thing, I had texaco gas in it when it wouldn't start and it clogged one of my injectors. Since then I've only been running mobil.

 

ttt

 

You haven't changed the fuel pump have you? I had a stock fuel pressure regulator in mine when I put the Walbro pump in and the fuel pressure would bounce just like you are describing. I put down the money for a Holley AFPR that comes with the new spring and diaphram and it cured the problem. Might be worth a try.

 

No, I have a stock fuel pump with an Accel regulator. Perhaps it may be the regulator.

 

pressure drop after shutting down is probably leaking/stuck injectors.

 

I pinched the return line and primed the system and it held the pressure. When I let go of the line the pressure dropped to 0 in about 25 seconds. This leads me to believe that the problem is the regulator.

 

Son of a bitch.....I just replaced the pressure regulator and it was wroking fine after I put it back together.......then it wouldn't hold more than 40psi. It was working great but then it started just sitting at 40 when I got on it. It holds when I shut the car off now. So now I have a new pressure regulator and a new walbro pump but still no fuel pressure.

 

Ummm say that again? It sits at 40 psi, but you don't have any fuel pressure? Stupid question, did you put the filter in the right way?

 

Lol, read the whole thread, smart *** My last post wasn't very coherant because I was furious, sorry about that. It won't hold more than 40 pounds of fuel pressure at WOT. Hell, it just sits at around 40 the whole time. I have the AFPR set for 50 at WOT. After installing the new AFPR it was spiking to 50 like it was set for but it only lasted for about 10 minutes. Could this be some sort of problem with the injectors that only shows up when they're hot? I'm getting pretty damn sick of taking the SuperRam plenum off.

 

Ok, now I unnerstans.

If you can't get it to hold pressure where you think it should be the pump might be on its way out.
Try running the car at idle and note the pressure, next remove the vacuum line from the regulator and plug it, note the fuel pressure now. If it dosen't go up when you remove the line then either you have the regulator maxed out or your pump is going bye-bye.

 

It's a brand new pump. I installed it last week. I know how to work the AFPR, lol. It goes to 50psi when I set it with the vacuum line off and capped. It just doesn't go to 50 when I go to WOT.

 

How old are the injectors and what flow rating are they? Try setting the pressure to about 40 with the line connected and car idling. Or set it as GM suggests, engine off, key on, let the pump charge the system and adjust to 43psi (will take several cycles of the key while adjusting).

 

Ok, thanks, i'll try that. The injectors are 24lb'ers out of a '94 Z28.

 

If the injectors were not cleaned and flow checked/matched before being installed it may be time to do that. You may have one or 2 injectors stuck open and starving the others causing a lean condition in some cylinders.
If you have access to an injector tester like the one Sunpro made, you could do an injector balance check and see if there are any faulty or stuck injectors.

This is the tester here.
http://actron.com/cgi-bin/web_store....id=1951293_504

 

ttt

 

I have the same problem. Brand new walbro pump, new filter, and holley afpr. i cannot get enough fuel pressure. I sent the afpr back because i can dead head the pump at 95 psi. i can only get a max of 42 psi with the regulator. I will let you know when i put my new one in what happens. I have to make it to the shop before it closes though to borrow a T-10 tamperproof bit.

 

Thanks, let me know what you find out.

 

Turns out that my FP gauge must have been off a little bit. What was wrong with the car was the distributer shaft

 

Ok, how about this. Try hooking a vacuum gauge to the motor and drive it down the road at WOT. See what the vacuum gauge reads. I've heard of instances where the intake bellows will suck together and starve the motor for air, causing an increase in vacuum, causing the regualtor to not raise the fuel pressure. Might be an easy check and fix.