Aopsahl7

Hey guys,

The battle with my fuel system continues.

Recently I installed a fuel pressure guage on the fuel rail so I could keep tabs on fuel PSI from inside the car. Anyways I started off today trying to fix a problem I have had for a while.

The problem is that the fuel pressure in the key on position (without cranking the engine) does not hold. You can hear the pump crank up, and the guage rises, but quickly falls to nearly 0 PSI. The engine will start and run fine, but starting it takes about 3-5 seconds of cranking (I assume due to lack of fuel PSI).

SO today I replaced the fuel pressure regulator under the plenum and made sure that the vaccuum line attached to it was getting good vaccuum. BUTTTT that did not fix it. So now I am coming to you guys.

What do you think it is?

C409

What is the pressure while running ?? I wouldn't be too concerned with what it does with the engine off .............

Aopsahl7

While running it sits around 50-60 PSI. Shouldnt it be able to hold its pressure at key on though?

ch@0s

Fuel injectors or fuel pump could be leaking down.

Aopsahl7

OHM tested each injector. I have a hunch that it may be something with the fuel pump assembly.

ch@0s

If I remember correctly there is a ck valve in the gas tank.
To verify the injectors you will need to clamp the return line on the fuel rail. Put a fuel pressure gauge on the rail and time how long it takes to leak down.

John A. Marker

... Here are the sure fail tests for the fuel system to save you time and money.. Take a fuel pressure gauge attach it to the Schrader valve.. Turn the key on and off a few times to build up the pressure in the system... If you are having starting trouble the pressure will probably drop as soon as it hits 38 or 40 and the pump turns off it will probably leak back to zero within a few minutes. Ok now right after you prime the system pinch off the return line near the tank if the pressure drop stops it is a bad fuel pressure regulator.... Next pinch off the feed line if the pressure holds then the leak is before the point where you pinched the line IE fuel pump check valve..hole in the metal line on the sending unit caused by it rubbing on the inside of the tank you should visibly be able to see this if you pull the pump and the sending unit...(this was my problem) or the pulse dampener which is the piece between the pump and metal line on the sending unit.. the diaphragm tears.. and last if you pinch both the feed and return line near the tank and the leak down of the pressure continues then a fuel injector is your problem.. This is the GM test.. saves time and money..

C409

[QUOTE=Aopsahl7;1575997444]While running it sits around 50-60 PSI. Shouldnt it be able to hold its pressure at key on though?[QUOTE]

50 - 60 psi is pretty healthy ... you must have an adjustable reg ... with the key on the pump only runs for a few seconds just to build pressure for start-up ... I really wouldn't worry about the drop-off if the pressure stays steady while driving ...........

Aopsahl7

Is the check valve built into the fuel pump?

Also, a slightly different problem, but same catagory. My Fuel level gauge is pretty inconsistent. It never seems to be right on. Any ideas about what is wrong with that? (Its not the cluster I just had that completely restored with new internals)

John A. Marker

Check valve is built into the pump.

cumbercr

There's another possibility that I found on my 85. My fuel pressure would only hold a few seconds after the switch was turned off. I went through the entire fuel system to include fuel pump, pressure regulator diaphram, and injectors. The problem turned out to be the fuel pressure regulator body. Apparently there was not a good seal between the diaphram disc and the regulator body return line. You could not see it with the naked eye.

Try clamping off the supply and return lines at the gas tank immediately after putting pressure to the rail. Make sure they are clamped off tight. If pressure holds, you know the injectors are fine. Then release the clamp on the supply line. If pressure holds, you know the pump is good. The regulator is the only thing left. It's just a process of elimination.