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Updated - See below. Definatly VERY low fuel pressure.
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My car is running lean and i'm going to be borrowing a Fuel pressure guage. I have a hunch that the cars not getting enough fuel either because of the fuel pump going bad or the fuel pressure regulator. I can see how a fuel pump works, but i'm not sure about the regulator. How do i test my fuel pressure regulator and how does it.. well work

I want to see if the problem's my fuel pump or the regulator... (as the fuel pumps a royal pain in the *** to fix...) Any help would be really appreaciated...

 

You can check the health of the fuel system by connecting a pressure gauge to the Schrader valve on the fuel supply hardline behind the passenger side fuel rail. Start the engine, and pull the vacuum compensation line off the fuel pressure regulator (behind the drivers side fuel rail). The fuel pressure should be 43.5psi +/-2.5psi, so anything from 41-46psi meets spec. Then reattach the vacuum compensation line, and the fuel pressure should drop in proportion to manifold vacuum. For a stock cam, that would be a 6-8psi drop. Less drop for a hotter cam. So... you are looking at 35-38psi with the vacuum line connected.

Tape the pressure gauge to the outside of the windshield and drive the car. Fuel pressure should respond to throttle movement. Push down fast on the throttle, and fuel pressure should rise close to the value it was at at idle, with the vacuum line off. Then take it out to redline. Fuel pressure should stay near the "no vacuum" value.

If it doesn't respond this way, could be:

-worn fuel pump
-clogged fuel filter
-faulty fuel pressure regulator.

When you pull the vacuum line off the fuel pressure regulator, it should not have any fuel in it, and should not have a strong fuel odor. If it does, good chance the diaphragm in the regulator has failed.

Just curious... how do you know its running lean?

 

Cell 14 and 15 are reporting 160's on the left and right BLM's. (spent a whole long weekend getting scanner educated and had some fun with some snap on diagnostic thing ). The integrators were also maxing out at 160's non stop too during the "stumble" which was cell 14 and 15 as well. I know the o2's are working correctly as they show fine fuel/air mixtures during the other rpm's. I didnt get a chance to floor the car and see the scanner at the same time, but when i do floor it normally the car (after around 4k+ rpm) feels like its has zero power and it just barely pulls. Periodically when i'm going WOT the check engine light will come on as well near the top of the rpm band and throw a code 55 (engine lean code).

I'm about 90% sure that this fuel leanness is causing my low rpm stumble and now this new dying at WOT. The car kinda doesnt really miss, just feels like its barely accellerating... Thanks for the info! Got me a fuel pressure tester yesterday and am gona find out which connections your talking about next I'm not too familiar at all bout the fuel system on our cars...

Oh, if you don't mind could you confirm that the vaccum thing im supposed to pull is what connects to the #10 on this diagram... http://csce.uark.edu/~jgbertr/rb/fuel_rail_94-97.jpg ?
Just wanna make sure i'm doing the right test The schraeder valuve is #7 i assume.. right?

Your post is going to be a huge help in helping me diagnose this

 

Yes, #10 is the fuel pressure regulator. The vacuum line connects to the nipple that points off to the side. When you pull the vacuum line off, plug the line up to avoid a rough idle.

#7 is actually the cap that screws onto the Schrader valve, and underneath that is the valve core. Your "test pressure gauge" should have a pin that depresses the core of the Schrader valve when you screw the connector on it. If it doen't, you need to remove the valve core with a tire valve tool.

 

Perfect thanks for the help, going to do the test right now! It's amazing how little you know about something until you do it at least once... even with craploads of reading n stuff haha..

 

Holy crap! I just did a fuel pressure test on my car and something is DEFINATLY bad. Very very bad. Normal PSI for key in the ignition is in the 40's mine was way down in the 23's. I bled the fuel out a bit using the gauge and key on engine off, onthe car again, same number 23PSI. Tried to crank the car and it took forever to start! Anyhow once idling it was staying around 23 PSI steady, if i gassed it a tad, it moved down to 22 psi or so. Something is DEFINATLY wrong.

Could someone toss a hand here? Do you guys think its the fuel pump or the regulator? Someone please please tell me its just my fuel regulator is it at all possible the return and feed lines for the fuel might have been crossed? I did have the engine rebuilt.. and am not too confident in the engine builder (after he had built it for me)...

When i disconnected the vaccum line there was little or no change at all on anything, the engine ran the same and there was no increase or decrease from the 23 PSI it was at.

 

Hey Injuneer, If the diaphram failed and there is a strong gas smell what problems will it cause ?

 

I would expect the O2's to detect the car running too rich as bit of fuel will likely be coming into one or more cylinders more than it should be (From the rupture). If its minimal it might barely be noticeable in that case i think it would cause lack of fuel pressure when WOT as the regulator wouldn't compensate as much as it should. Tiz only a guess but im going on what i know about regulators.. if they work the way i think they do