Cliff notes before you all give up!
Injectors OK, no leaks. Fuel pressure dropping like a blind roofer.

OK, long version now!


First, here is what I am running:
Walbro 255 pump
Aeromotive FPR
Stock TII 550's
Ford secondary 1600's

Have a problem here. I think. Last week I had finally gotten my rebuild together and the engine fired, ran, then died in a few seconds. After trying to start it after that, it never did run. I suspected since it was a fresh rebuild, it could be flooding. I figured correctly. I checked the plugs and they were stinky with fuel. I noticed after priming my pump, the pressure would drop (I have a gauge) extremely quick. Within 2 minutes it would go from 35-40PSI to nothing. At this point I had the manifold off so I could see the system in it's entirety. No leaks on the rails or lines anywhere. I suspected it was an injector. I sent my injectors out for service (thanks KG!). The results... AHA! Leaky primary injector! Post cleaning/service everything is great; leak test passes!

I reinstalled the injectors tonight. I wasn't planning to start, I just wanted to prime it. After priming I got the usual 35-40PSI. After 30 seconds or so, it was down to nearly 20PSI After 5 minutes or so it was around 20, maybe a bit less. I didn't stick around, as I was pretty mad and it was getting dark.

It's not dropping like before, within 2 minutes, but it's still dropping too quick I think.

Something tells me this can't be right for fuel pressure drop like this. Maybe it's my FPR not set right? I should note my car ran 2 years ago until I blew it (I screwed the timing, my fault) so these parts have all been sitting 2 years.

Regardless. What is happening? I will try to start it again regardless tomorrow.

 

my Aeromotive FPR loses pressure in seconds once the pump is off and I have no problems...

what is triggering your pump? What engine management do you have? With stock style wiring the circuit opening relay needs to be triggered by something once the key leaves the "start" position. On the factory ECU the AFM provides that ground, or the fuel pump check connector. If you have a standalone you need to make sure that its fuel pump trigger is set up correctly. try jumpering the fuel pump check connector and leave it hooked up while you crank the car over.

 

I run a haltech E6k. The car primes when the key is set to on. I didn't think this was normal for the pressure to drop that fast. If this is normal, then I should be OK. I will try starting the car tonight.

 

It is not normal and it is not something that you should dismiss as no problem. Fuel pressure should hold for hours.

As I told you before Arghx, that is a huge problem. Do you have a fuel pressure gauge inside your passenger compartment? How do you know your fuel pressure is not bleeding off when you go into boost? Every car I have ever seen with a fast fuel pressure bleed off had a problem with pressure drop in the high rpms/boost.

Beefhole, you have already solved the leaking injector part of the issue, now it is down to the pressure release valve in the Walbro or a piece of debris hung up at the ball valve in the FPR. If it is the fuel pump, there is a very good chance that the release will pop open when the fuel pressure should be rising to accommodate boost. The good news is that Walbro pumps are inexpensive. To check the FPR just remove the 4 screws and inspect the ball valve in the middle of the diaphragm. I have also found that a basic test for a weak pump valve is to try and raise the base pressure to 65-70 psi with the FPR, if the pressure starts bouncing and pulsing at around 50 (or if you find that you can't raise it above 40 at all) then the pump needs to be replaced.

 

Thanks for the help. I will inspect the FPR tonight. As for the walbro, I hope I am understanding right. You're saying the valve can be getting stuck open, and without the pump running, my fuel is flowing back via the supply line?

 

The pump has a check valve and a safety valve either could be bad. I have had the safety valve fail in several walbros, causing erratic lean conditions

 

lame, that seems to be like what I'm dealing with. Randomly runs lean and sometimes under full boost it'll just start creeping leaner and leaner like the fuel pressure is dropping...

Do you think spending a good chunk more on an aftermarket nippondenso from say rx7.com would be worth it?

I'm almost about to do it because my walbro is really loud, and it only has like 10000 miles on it

 

Strange. Not that I don't believe you (there is a lot of room for you to be completely correct) or that it isn't also a symptom of a failing pump but that contradicts what I was told by Aeromotive techs. I noticed this same problem straight away after installing one many years ago and suspected a bad regulator. I called Aeromotive and the tech that I spoke to explained to me that holding pressure for > 20 minutes was an emissions concern (to avoid poor hot-starts due to excess cranking I guess.) He went on to say that this behavior is completely normal on their FPRs. At the time I had tried it with 2 different pumps (original FD and a brand new cosmo) and had the same reaction.

I do not log fuel pressure, so I don't know how much it drops (I'm sure it drops a but due to low voltage.. I have not rewired the pump) but duty cycle has remained fairly consistent over the years.

..for what it is worth.

 

Dropping pressure to 0 within seconds of the car being turned off is not normal, even with a stock FPR. After 20 minutes it should still be at least 20 psi based on a regulated base pressure of 40 psi. Sounds like the tech at aeromotive was trying to avoid dealing with a warranty issue. However 9 out of 10 times it is the pump that has failed. I have only seen a few bad Aeromotive FPR's, typically the owner had installed SS lines but failed to clean them out before installing, this led to metal wires damaging the ball. Others have small pieces of teflon tape from improperly applied fittings.

 

Even the FSM fuel pressure holding spec for a completely stock fuel system is to maintain a minimum of 18-21 psi after 5 min. with a prime time of 10 seconds.

 

Not trying to be argumentative or beat a dead horse here.. I leave plenty of room for being lied to by tech guys... but his point was that an OEM FPR has a specific requirement to hold pressure and racing parts do not. The argument that "even a stock FPR holds pressure...." really goes to his point. His point was that their product was meant to flow more, be adjustable, etc... but not necessarilly engineered to hold pressure after shutdown.

All that said, I have a good oportunity to go through my fuel system soon and will go through check valves in the pump and polish up the seat on the FPR ball.

 

bringing up old topic. how do you know if its a fuel pump issue or the specs of the after market FPR. is there a test to do with the fuel pump minus the FPR to see if the fuel pump is at fault or the fpr