My pressure goes to 50 psi then immediately drops to zero.Is it the fuel pressure regulator or could it be some thing else.This happens with the key on off test and jumper wiring the aldl g fuel pump circuit.

 

Regulator, checkball in the pump or injectors and areas where fuel pressure will leakdown.

 

with 383vett.

Here is the information you need to continue...

••••• TESTING FOR LOSS OF FUEL PRESSURE

... 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..
•• disconnect the vacuum line from fuel pressure regulator

 

Had the same issue on my 87 just put in a new fuel pump regulator tested fine.

 

Well I took the plenum off today.I changed the diaphragm in the fuel pressure regulator.Same problem,50 psi then zero.Did the fuel pump check per factory manual 50 psi.I could here the fuel passing through the back of the fuel rail.Pulled the fuel rail and new injectors I bought.Put the old injectors back in and pressurised the system.It held pressure like it is supposed to and no leaking injectors. I suspected it was the new injectors because the engine seemed like it was hydro locking .I hope I didn't ruin my engine.It's holding fuel pressure now I just haven't tried to start the engine cause I worked on it all day and wanted a fresh start in the morning to see if I damaged my engine.

 

Pull the plugs out now if you suspect the injectors were leaking fuel into the cylinders. Check oil level and can you smell fuel on the dip stick. At 50 psi you can dump a lot of fuel into a cylinder.

Did you find fuel in any of the cylinders? if so.... I would also pull the red hot wire from the distributor and turn the engine over. If you find one or more cylinders with fuel. Try and get out as much as you can. Perhaps hit the cylinders with compressed air if you can. Then squirt a small amount of oil into the cylinder....since you probably washed down the walls with fuel and have removed all the oil that was lubricating the walls.

 

When I had the plenum off and the the old injectors and fuel rail back on I cranked the engine over and blew any excess fuel out of the cylinders through the intake runners.I am going to change the oil befor I try to run the Vette

 

Steven,
I just had that same occurrence on MY '90. I did the 'pinch test' on the return hose at the tank, no change, did the same on the supply hose and my pressure held. Have someone turn the key on a couple of times while you are at the fuel tank. Pinch the supply line as soon as you have 50psi on the gauge. I'm betting the fuel pump is bad if you have known good injectors. My check valve is bad in my almost new fuel pump. I'll just live with it. It starts great and holds 39psi running and 48psi vac hose off engine on.

Mick

 

is the pump priming?

 

Thanks for all your responses guys I will try all of your suggestions.Yes Z-51 the pump is priming.