I have a fuel pressure problem. The system (with gauge on test port on RH fuel rail) will get up to pressure, then immediately drop when I shut down.

I was hopeful that it was the check valve. I checked the check valve by pressuring up, then clamping the feed hose to the pump. The pressure still dropped.

Two possibilities I see: leaky injector (really leaky -- the pressure drops from 60 to 15psi in seconds) or faulty return. (No gas smell in vacuum hoses coming off regulator and dampers.)

How is the fuel return supposed to work? It seems to come off the front fuel damper; does this damper also act as a pressure regulator? Would a faulty front damper cause a pressure drop like this?

Any other possibilities?

Thanks,
Mark.

 

Your arrows are reversed.

#5 is the front damper from the fuel feed through the rails to #3 the rear damper and #4 the regulator to the fuel cooler and back to the tank through fuel hose 10a.

Check the dampers and the regulator with a vac guage.

Have you checked the spark plugs to see if any are wet with fuel?

 

The difference between 60 PSI and zero is a few DROPS since liquids do not compress. The S-4 is supposed to hold 3 bar of pressure for 20 minutes. The only fuel pressure regulator is the one at the rear of the passenger fuel rail it acts as a check valve on the fuel return line. Pinch off the rubber return hose on the top of the fuel tank ( under the carpet /black access circle ) jumper the fuel pump for a moment and see if the system can hold the pressure.

 

Ah. Suddenly it all makes more sense, Malcolm.

Jim, I did, and the system didn't hold the pressure. I'll go try again after dinner, and make sure I've sealed the hose off. If it still won't hold pressure: injector leak? The injectors had recently been cleaned and were working fine when I took them out; I haven't yet started her up after my intake refurb, so if one is leaking it might be dripping down onto closed intake valves.

 

Okay. It holds pressure much better with the return line clamped. So: bad FPR. (Also need a new o-ring between the gauge and the fuel rail, but that's a relatively small seep.)

 

If you haven't done it so far with the FI and intake work consider all fuel lines especially the ones at the back of the engine.

I have a stock FPR sitting in the parts bin but the shippin's restrictive.

 

https://rennlist.com/forums/showthre...highlight=edco

Edco had this exact problem....it was the fuel pressure regulator!!

 

Malcolm, I did all of the fuel lines.
Brian, I didn't want to believe that my $175 928 Specialists FPR was defective out of the box. I talked with Dave about it today, and he reported:

So I'm going to button everything up, roll her out, and fire her up.

 

[/QUOTE]Malcolm, I did all of the fuel lines.[/QUOTE]

Excellent

Brian, I didn't want to believe that my $175 928 Specialists FPR was defective out of the box. I talked with Dave about it today, and he reported:



So I'm going to button everything up, roll her out, and fire her up.[/QUOTE]

I have 928 SP FPR and it doesn't do what your does..........perhaps jumper the FP relay and adjust the FPR to their suggested pressure above stock, remove the jumper and time the pressure drop...........Jim listed the spec.

 

Malcolm,

That's what I've done, and the pressure drop is quicker than the Porsche spec (and Jim) say it should be. If your 928 Sp FPR doesn't do what mine does, then Dave is mistaken.

I'll button a couple of other things up, test it again, and report back. Thanks for the help.