Yesterday, I changed the 6" rubber fuel hose that attaches to the rear of the fuel rail because my old line had a pinhole leak in it. Before changing it, I relieved fuel pressure by pulling the fuel pump fuse and cranking the car. After changing the fuel line, I put the fuel pump fuse back. Now comes the strange part.

I tried starting the car and noticed that it took longer than normal. So I tried again. I turned the ignition off and then back to on. When I did this, I noticed that my fuel pressure gauge immediately jumped to around 40psi (which is normal), but then fuel pressure quickly fell to ZERO. It literally drops from 40psi to 0psi in ~5 SECONDS. It does this everytime I turn the ignition from the off position to the on position.

Even with a bad fuel pump check valve, shouldn't pressure slowly rise if I keep the ignition at the on position? It doesn't. Also, I don't think it's a leaky injector (how could changing a simple fuel hose immediately cause an injector to leak?); it must be one hell of an injector leak if fuel pressure drops from 40psi to 0psi in 5 seconds. I don't see or smell ANY fuel. Moreover, I am 101% sure that the fuel line that I replaced is secure and leak-free.

Now, if I want an easy start, I have to turn the key to on while watching my fuel pressure gauge. When I see the fuel pressure jump to 40psi, I crank the engine, and it'll fire up just fine.

What could be the problem? I didn't have this problem before changing the rubber fuel hose (and cranking the car w/o the fuel pump fuse, which I've done many times before) yesterday. Again, I can't SEE nor SMELL any fuel at all so I'm sure it's not a leaky fuel line.

 

Fuel pressure regulator perhaps... was the gauge upstream or downstream of the FPR?

 

The fuel pressure gauge sending unit is installed right after the fuel filter, which is upstream of the FPR. Anyway, I doubt the FPR is bad. Fuel pressure from idling to n/a WOT to spraying nitrous is normal.

I just find it highly strange that I would have this problem right after simply replacing a fuel hose...=P Having residual fuel pressure drop as fast as mine does seems indicative of a non-existent fuel pump check valve!!

 

That is strange... Now I'm really pulling ideas out of my a**, but you could try another fuel pressure guage?

I guess you know there is a fuel pressure problem though, since you said it only starts when the guage reads 40psi.

Is there is a check valve? I didn't even know that. Is it part of the pump or a seperate replaceable part?

 

haha...thanks for the suggestions, but I'm sure my fuel pressure gauge is working fine.

Yeah, there is a fuel pump check valve and I believe it's built in the fuel pump. It prevents fuel from leaking back into the fuel tank when the car is off for easier starts.

Hmm, I think I'm answering my own question. =P I'll plan to do some tests tonight (clamping the fuel line in certain spots & monitoring residual fuel pressure drop off). It seems as if the check valve went bad all of a sudden...

 

Sorry I'm not more help ...

Do you see the fuel pressure build up as you crank? I'm just trying to get a better sense of your problem to help you isolate...

I'm not sure how you'll clamp the fuel line.. you'd almost need a second person to help - i.e. get the fuel pressure up to 40psi, and then put the clamp on...

Unfortunately fuel pumps aren't cheap...

 

If I try to start the car in one continuous motion beginning from the off position (like most ppl do), fuel pressure will continously fluctuate up and down from ~40psi to ~20 psi. It will do this for a few seconds before the motor will actually fire up.

I plan to clamp the return fuel hose in the engine bay, turn the igntion to on (thus pressurizing the fuel rail, lines, basically everything before the return hose), and monitor the fuel pressure gauge. If residual fuel pressure doesn't drop, then it's most likely the check valve.

 

I need to get a fuel-pressure gauge on my car. I have extended cranking too.. and its consistently extended... I know i30ds had the same problem and it turned out to be his fuel pump. FYI, he tried a Napa pump and it ended up being faulty out of the box, so used a OEM one instead. He highly recommends an OEM replacement fuel pump.

Your idea on the clamp sounds fine... so the check valve is on the return side... (if I understand correctly).

 

Even when you turn off the car, the fuel pressure does not drop to zero quickly. It gradually migrates itself on down. Your fuel rail is not maintaining adequate pressure...not even close. I would have to suspect the fuel pump.

 

Yes, I know it's not supposed to drop to zero quickly. That's the point of me starting the thread. =)

I suspect the fuel pump (check valve), too.

 

The only question is, why would ANYTHING go bad after changing a piece of tubing???

 

That's the question I want answered, too.

Assuming that it is the fuel pump check valve, I can only think of 2 possibilities.

1) The fuel pump check valve was already on it's way out; it's just a coincidence that it completely crapped out at the same time I changed the tubing this weekend.

2) Before changing the fuel hose, I cranked the car without the fuel pump fuse to relieve fuel pressure (I've done this many times in the past w/o a problem). Perhaps this last time "aggravated" the fuel pump in some way, although I don't know how. I'm pulling ideas out of my *** now, too. =P