If the engine has been running for 5 minutes or so and I shut it off, should there be fuel pressure at the shrader valve when I shutoff the car? If there is supposed to be pressure, what would cause there not to be any pressure? Bad FPR? REALLY leaky injector? I ask because I can completely remove the shrader valve seconds after I shut off the engine. Hmmm...

 

Okay VetteNoob, I'll get it started here. The couple of times that I've worked with the fuel rail I've always experienced pressure at the shrader valve. My LT1 seems to develop (and hold) pressure on the fuel system even after I've attempted to relieve it by opening the gas cap. Once I tried changing the fuel filter after the car had set overnight and still had enough pressure at the shrader valve to cause gas to stream up onto the windshield! Now as far as why you don't experience pressure after running the car for 5 minutes - hmmm, I really don't have a guess for that. When you say you're removing the shrader valve seconds after running the engine - are you just taking off the cap or are you literally removing the valve inside the shrader fitting?

:seeya

 

Soudsn like a MAJOR fuel injector leak.
I have a slight leak in mine I think, as pressure drops after I turn the engine off from 45+_psi to under 20 within a few seconds, but It retains like 10psi for a logn time still somehow. Like for example, I had the car in the garage for over a week, and I purged the fuel from the shraeder valve to work on the engine, fuel splurted out still (into a container of course). If you lose all pressur eright away, I'd say either your injectors are totally leaking, or it is something on the fuelpump-engine fuel line or the pump itself? I am not sure.. Let us knwo how you make out.

:cheers:

 

I had the same trouble on an F-Body. Checked it for a leaky injector. No problem there. Ended up being the check valve in the fuel pump.

 

Get a normal fuel pressure gauge and start doing the tests to see if you have leaky injectors.

 

Have or did you just put an adjustable fuel pressure regulator on?

 

Boy, I sure hope it isnt the FP. It was just replaced about a month ago. I do suspect it is a leaky injector as I usually need to hold the pedal to the floor for a few seconds before I start the engine again if it has been sitting for a while. I dont have an AFPR (yet). This is on my list of things to get.

Scorp, can you explain what you mean by a normal FP gauge as opposed to the electrical ones you can get for the interior and how do I go about testing the injectors for leaking.

Oh and as for removing the shrader valve, Im talking about the whole valve and not just the core. I can completely remove the valve without leaking a drop of fuel.


[Modified by VetteNoob, 12:23 AM 12/22/2002]

 

I'm not sure then, the AFPR's will leak vacuum around the adjustment screw & thus let the pressure bleed off. My Aeromotive does this & when I swap my stock fuel regulator back on it immediately holds pressure again. :)

 

I just mean one of those $25 ones from autozone that have a hose on them that you screw into the scrader valve. First thing you want to do is stick that on and turn the key 'on' but don't start the engine. The fuel pump should prime the system for about 3 seconds. When the pump stops your fuel pressure should hold relatively steady.

There is actually a set amount GM says it should go down over a period of time before becoming concerned, but I cannot remember what that is right now. I'll get the book out later (on my way to the gym now) and take a picture of the test procedure to test for a bad regulator, leaky injector(s), or check valve in the fuel pump.

 

:iagree:
I just went through the exact same thing on my 96 and it wound up being the fuel pump/check valve. (Is yours having a hard time starting when its up to temp?)

 

You can narrow it down to the FPR, injectors, or pump fairly easy.

First, as Scorp mentioned, make sure you have a decent mechanical gauge to screw onto the rail. The $25 one from the parts store is fine - you don't need anything exotic.

Most the steps here are easier with a helper (pretty much impossible without). You're going to need to get to the top of the sender at the back of the car. It's the easiest place to do all this and rules out lines and such (not that that's your problem). It's easy to get the lid/bezel assembly off and pull the rubber boot out. Next you'll need to determine which hose is which back there. This is one thing I can't tell you for sure. I'm not sure if all years are setup the same and I don't want to guess. Maybe someone can point us in the right direction. You'll have a pressure hose, a return hose, and I believe a third one for the vapor canister.

Once you get them figured out, here's what you do:

To test the FPR:
Have someone sit in the car ready to turn the key on. Be ready to pinch of the return hose as soon as the pump stops (or just a tad before). You may want to have them cycle the ket a few times to get the timing down. Keep in mind that you have to leave the key off for 10 seconds or so each time to get the pump to cycle again. I've got a set of needle-nosed shaped vice grips that I use. That way I can clamp them on and go have a look-see for myself at the gauge. If your helper can get out and read the gauge for you you can use a regular set of needle nose. Don't be afraid to squeeze it fairly hard. You want to make sure to get it sealed well. If the pressure stays up a noticeable amount longer and higher than it was before then your FPR is bad or not working right.

Next is the pump itself:
Do the same as mentioned above but on the pressure hose. This HAS to be done as close to possible at the end of the pump cycle for obvious reasons. If the pressure stays up now then the pump is bad.

If neither of the above seem to help a noticeable amount then it's most likely one or more injectors.

Hope that all made sense. I tend to ramble somtimes and lose focus. Let us know what you find when you do. -Jeff

 

Thanks for the info guys. Ill look into this and see what I can find.