As some may know I'm having a fuel pressure issue. New FPR Diaphragm, new FP and new Bosch III injectors. Still leaks down.

What I've done

Replaced affore mentioned items, not once but twice!

Raised car up and looked for fuel line leaks, couldn't find any.

Put paper towels around fuel rail connections looking for gas, couldn't find any.

Primed the heck out of fuel rail and looked and smelled for leaking fuel in a closed garage, couldn't find any.

Done the fuel line tests so many times I dreamt about it last night!!

So what I am going to do now

I am picking up a line valve, with turn off, to hook up to my fuel line/return line to get a more accurate test than pinching the lines in order to do the tests again.

I also picked up a cap to cap off off the fuel line so I can do an independent test on the lines themself in order to try and isolate the problem to the fuel rail or injectors. ( I got the injectors from Jon and he's been a huge help but we can't seem to find the issue)

Here's my question. Can I close off the fuel line and do a pressure test, by letting the pump prime, on the line itself without damaging anything. I've never done this before so input would be welcome.

I'm at my wits end on this and I have a leak down somewhere and can't find it.

I also have a couple questions. I changed out the diaphragm on the FPR. Is there any other thing that can and does go wrong with the FPR?

When looking in the ports for the bottom of the injectors, the ring around a couple of the ports seems off center to me. I didn't think that should matter or cause a fuel issue but I guess I just want to address any possibility.

Input is GREATLY appreciated. I will address that stupid idle stumble at a later date

Thanks

 

Have you tried a different pressure gauge? I don't have any personal experience with capping off the return line, but I can't see how it would hurt anything. Good luck.

 

Actually I have not. I was thinking about that as a possibility but I have a cold hard start issue and when I prime the pump 2 to 3 times it seems to start up ok. Some days it seems to fire right up.

 

You may want to check you lines for the emissions evap canister. My canister went bad and the charcoal plugged up the line and the line from the tank to the canister may be leaking back as the valve may be bad also. Mine is a '93. Took a while to clean out the plastic line that goes to the front. Replaced oem lines with new hoses and the valve. On mine removed tire, inner fender liner, plastic cover on right rear fender.

 

Hmmm, I thought of that as a possibility also. I did replace the first line, that goes from the tank to the connector/valve?, because it looked all boogered up. I'll have to do some research on this.

Can that cause a leak down issue?

 

I had this same problem. It went away when I put in a new FPR body. This was after new injectors, FPR diaphragm, cold start delete and new fuel pump.

If you block off the return to the tank, you can run your pump briefly to find out max pressure and bleed-down for all but the return line (pump check valve, injectors, etc.).
After I did this, and the pressure held, I was certain it was the FPR base/body. A search showed at least one other forum member had reported this same problem/solution.

I got the complete FPR through Rock Auto. After installation, the pressure did not hold right away. A simple turn of the key didn't do it, no matter how much I bled the pressure gauge line. It did hold perfectly after running the engine.

Good luck

 

you know I was actually starting to lean this way, but I didn't know if the body could be the problem for sure.

I have pinched the lines and nothing held so my valve cut off should tell me more.

I did block off the return line a couple times and the pressure went up to 60 and held. But here's the weird thing. I could get it to do it a couple times but themn it wouldn't hold either and I couldn't duplicate it

The reason yours wouldn't hold at first is because you had air in the system. You have to either bleed the system through the rail with your valve by releasing the pressure on your gauge or start the car. FWIW

Thanks,

edit: Oh, I see you did bleed the line. Oops

 

How quickly is your fuel pressure bleeding down. In my opinion, a slow bleed down is acceptable. I had a fuel pump that bled down to zero in 10 seconds or so, but there was still enough pressure and volume to run 10.60s at the correct afr.

 

it varies. Sometimes it drops to 20 pretty fast and then slowly goes to zero in about 1 minute or so. Then sometimes it drops steady to zero in about the same minute.

 

The first thing I'd do is to determine if the pressure drop is being caused by something up front or out back. There are ONLY a few places that can cause the pressure NOT to hold.

As you already have, use the clamp the hose procedure to ID front or back. If you have NO external leak, pulling the fuel pump and installing clamps on the pump hoses and/or replacing any that seem worn/brittle/cracked/leaking will solve the out back issue. All the rubber fuel hoses should be suspect. If they're hard, replace 'em; hard doesn't seal well.

Replace or eliminate the pulsator (I believe it's called). On my 86 I replaced mine with a short length of fuel hose and clamps. Could never tell it wasn't there.

Up front it's got to be the fuel pressure regulator and/or injector(s). Anywhere else would show up visually.

Jake

 

tried all that. new pump with hose instead of pulsator. Double checked that as well to make sure it was tight and seals and even replaced the hose although it was only a few months old.

Can't find any external leaks at all.

But I do know one thing, it's leaking down somewhere somehow. I'm going to try the shut off valve thing and see if that won't isolate the problem better than crimping the line.

Is it possible to be leaking air and not fuel? I don't think so.

 

Your guess is as good as mine.

Hell, it could even be the fuel pressure gage you're using. At this point I wouldn't discount anything.

Jake

 

Never run ANY pump 'dead-headed' (100% no flow), even pumps handling pure water have experienced explosions when run with discharge flow totally shut off...isolate piping section in question with caps/etc and use 50 psi orifice flow restricted compressed air with air feed disconnect to assure no 'extra air' enters during test, pressure gauge in test zone, remove tank fill cap....after pressurizing test zone with comp air (NEVER use oxygen) remove air supply link and watch gauge, 'soap solution' at suspected external leaks may be useful, audible 'hissing' inside tank may indicate leakage inside.

 

A pinch test is only as good as the pinch. If you not 100% pinching off the flow, you will have leakdown and won't know exactly where the loss is from.

Good Luck, I hope you find the problem.

 

Thanks guys!

Last night I installed my fuel shut off valve back at the tank and connected my return line to it. It took a couple primes to pressurize the system but once it did get pressurized it shot up to 60 and stayed there for a good while. Then it very slowly leaked down to 50 and then even more slowly to 40. This held for at least 20 minutes before I released the the pressure some and then shut it back off. The pressure fell to 10 and stayed there.

SO, what I am now convinced of is the FPR body itself is shot. (is there some kind of check valve in these things?)

Anyway, would anyone disagree it's the FPR body? All indications seem to say it is even though the diaphragm is new. (I know nothing about the workings of the FPR other than the regulate fuel pressure)

FWIW, the valve and fuel line is a very efficient way of checking the FP system IMO.

Here's a picture of a valve similar to what I installed. Then just attached a piece of 3/8 inch fuel line to one end and your line to the other end and then test away. works way better than pinching and way more efficient.

http://www.rcaccessory.com/newfuelshutoffvalve.aspx

 

Mike are you saying that all of these problems started after you replaced the fuel injectors ?

 

No I had a bad FPR when I bought the car. I replaced the FPR diaphragm, and while I was at it I went ahead and replaced the FP and the injetors so I would know the history of them since I didn't know when they were last changed.

At first everything was fine and then it happened again. I always suspected the FPR so I replaced the diaphragm again but it didn't work. I tried and tried to get an accurate test and everything pointed to the injectors.

After mucho work and help from Jon I couldn't isolate it. so I came up with a better way of testing fuel pressure that didn't leave room for error. And now I am almost 95% sure my issue is the unit itself and not the diaphragm.

Moral of the story. Always go with your instincts. But it's difficult to when you are only a shade tree mechanic and never worked on a TPI system.

 

Ironic, I too have a stock 90' L-98 that is presenting a very similar issue. If you would like you can view my related posts here:
http://forums.corvetteforum.com/c4-t...tor-d-c-s.html
http://forums.corvetteforum.com/c4-t...er-key-on.html
Very curious to see how you get things resolved. I ended up pulling my injectors and there on the way to Jon for testing. Like you, my instinct leads me to believe it's not the injectors. The issue with the FPR body is new to me? So today I pulled it apart to take a look. Both the seat and the disc appear to be ok.
A couple pics...

You can see the nice, even ring where it contacts the seat


The darker area is discoloration. I checked it closely and found it to be nice and flat in the seat area

 

I have read a couple times people having to replace the body due to the diaphragm not seating on the body properly and another one who couldn't tell what it was but replaced the body and it cured their problem.

Also Rich Silvestris responded here and said he had the same issue and it was the body.

what the heck, I'll change it out in a couple weeks and see if that's the problem. right now that's the ONLY thing I can make sense of with my checks and rechecks.

i'll definitely come back and post my end results.

 

You blocked the return with that valve, but what are you using to block the feed line. If the check valve or pulsator are failing, you will lose pressure.

Maybe another valve is in order.