pletzvet

85 Coupe
Other than the smell of fuel in the FPR vacuum line or the presence of fuel, is there any other indication that a stock FPR is failing?

The reason I am asking is after going through the diagnostics for loss of fuel pressure, I'm still at a bit of a loss for a conclusive diagnosis.

There is no smell of gas or fuel in the vacuum line.

Here's the symptoms:
1. Fuel lines unpinched at the tank, turn on key and prime system for 2 secs - pressure goes from 0 to 34 lbs instantly. As soon as FP stops, pressure drops to 8-10 lbs within a minute or so.

2. Pinch the return line, turn on key, system primes to about 60 lbs instantly and holds. As soon as I unpinch the return line - pressure drops to 8 - 10 lbs within a couple of minutes.

I don't think I have a pulsator or FP check valve problem based on the diagnosis...

car5car

Regulator

pletzvet

Thanks for your (brief!) response - however, what I really need to know is - given the diagnostic information that I have gathered...what exactly is happening with the FPR that is causing these symptoms.

383vett

The fuel pressure regulator has 2 components (along with a spring); a diaphram and a seat/disk assembly. If the diaphram fails, the regulator will not hold vacuum and fuel can seep by the leaking diaphram into the line and intake. If the seat is not sealed against the disk, fuel will leak by and not hold pressure when the pump is turned off.

jmrl98

When my diaphram went bad, gas was in the plenum...

pletzvet

Your answer is helpful...just a little more details - since I have no fuel leaking into the line/intake, I am thinking the diaphram is okay (old, but okay and probably should be replaced anyway), but will test with a vacuum pump. However, can you tell me a little more about the seat and the disk...is this located in the body of the FPR or is it part of the diaphram kit?, and if it is leaking and therefore not holding pressure is there a fix or is this a replacement? The OEM delphi FPR is hard to find - the best that I have so far is a back order on the whole FPR - part # FP10009.

Thanks

EastCoastHD

RockAuto.com $72.99

John A. Marker

If the diaphragm was broken, it would allow fuel to seep to the other side and therefore enter the vacuum line. It is the diaphragm that fails in the regulator, not the spring as indicated by your reading of 34 PSI. I do not believe the regulator is at fault. It is built to allow pressure (for the 85) to reach about 34 pounds and then return excess fuel to the tank. When you pinched off the return line your pressure went up to 60 which is the highest pressure the stock pump generates and the pressure held. If you had bad/leaking injectors, the pressure would bleed off at this point, but it did not. This would indicate to me that the check valve in your fuel pump is about shot and is bleeding off pressure. If the check valve was good, your pressure should hold at 34 for about an hour and slowly bleed down to 6-10 PSI in about 12 hours.

Go for a new fuel pump.

pletzvet

So, I just did a vacuum test at the FPR with my vacuum pump. It held steady at approx 23 inHg or 11 psi. This confirms the diaphram is not leaking.

I started the engine and then pulled the vacuum line to the FPR. Fuel pressure jumped from 34 psi to 39 psi. The fuel pressure guage needle is not bouncing around. Re-connected the vacuum line at FPR and blipped the throttle - the fuel pressure increased momentarily to approx 37-38 psi and then settled to 34 at idle.

Shut the engine off and, as usual, the fuel pressure started dropping immediately and was down to 8-10 psi within a minute.

Based on my previous posts, I have eliminated injectors, cold start valve, any leaks/blockages in the lines. I really don't want to guess this one through, if I can help it.

Remember...when I pinched the return line before priming/pressurizing the system, it held steady at approx 60 psi as soon as it primed. When I pinched off the supply line only after pressurizing the system I still had the same leak down as soon as I unpinched the return line. (This makes me think FPR) Incidently, pinching the supply line when the system was holding steady at 60 psi (i.e with return line pinched), it pushed the reading to approx 70 psi.

I'm now questioning if the head pressure created at 60 psi is making the check valve in the fuel pump seal, but not sure whether it is completely sealing when there is no head pressure??? Alternatively, with the lines unpinched and when the system is pressurized during the 2 second prime, the fuel pressure guage hits 40 psi as expected, but then if the FPR is working properly, it would naturally release pressure to 34 and then hold there, would it not?... I'm thinking that it should hold at 34 and this is where I'm at a loss...Seems that I am down to 2 possibilites and I cannot eliminate one or the other - is it leaking at the seat in the FPR or at the fuel pump?

rons85

Pinching off the return line causes the drop in pressure to not happen = regulator seat not sealing well. And proves that the injectors aren't leaking.

Take the regulator apart (yes, this means taking the manifold plenum off) and you will probably find that there has been water collecting/pooling in the cavity around the Seat located in the fuel rail section. This seems to be a low spot and for whatever reason if there is Any water Ever in the fuel, it finds it's way here. It Also causes the stamped steel spring retaining ring on the regulator assy to rust. If the rust gets Bad enough it will prevent seating at all.

Water here will not corrode the (apparently) stainless steel seat,or the stainless sealing disc on the regulator assy, but will encourage crud to stick here and this crud will ruin the leak-tight seal.

Take it apart and see what you have. You will need the "security" type Torx bit for the OEM screws, if they haven't been replaced with non-security type yet.

Or - the bare fact that fuel pressure drops rapidly after the pump shuts off, while it's not Supposed to happen, really doesn't hurt anything. As long as the regulator is sealing well enough to get the pressure Up where it should be, quickly after the pump starts, then there are no negative side effects that will bother anything.

As long as you Know that the pressure drop isn't because of leaking injectors, don't worry about it. It doesn't matter..

pletzvet

rons85,
Thanks for sharing your thoughts/experience. I'm leaning toward the same conclusion about the source of the leakdown problem. Just for curiousity and preventative maintenance, I'm going to go ahead and update the FPR diaphram when I go in and inspect for corrosion/build-up at the FPR seat. I noticed that the #10 torx studs are indeed the safety style and will need to get a special bit for that. I've got them in other sizes but not #10.