Fuel pressure would go up to 41 psi with key on then drop, not slowly quick and to 0 psi. It's a 96 z-28 and runs and starts well. Just replaced o-rings on all injectors (just because they were out) and replaced fuel pressure regulator. But no change, pressure still drops to 0 psi. I can here a air leaking (hissing) sound at the rear, seems like it's coming from the fuel tank. I realize the system bleeds back to tank but can fuel pump start and run the car and still not hold pressure? Should I replace fuel pump? What a good aftermarket in-tank pump?

 

The car will run and stay running? If so then it's not the pump, i

 

maybe your guage is faulty or just the place in the fuel line your getting the reading from, no car will run @ 0 psi.

 

from what I am reading I think he means key on engine off... I think... if that is the case it kinda sounds like the fuel pump is bleeding back into the tank, maybe going bad...

 

check and see what your fuel pressure is when running and thrn when not running....thast is before it drops to zero. if it is higher when running, the fuel pump is bad. it will run high because of the voltage jump you get when the car is running. sounds like a pump to me

 

Sorry didn't explain properly, test is with car off. System is to hold pressure, and doesn't drops off to 0 psi. With car running it stays in the 40 psi range, no real drop. It's the drop without car running that is the issue, the system is to hold the 40 psi and it doesn't.

 

There are four things that can cause the pressure to drop quickly.....

-leaks in the fuel lines.

-leaking diaphragam in the pressure regulator. You should have checked the vacuum pump before replacing the regulator, that would have told you if the regulator is the problem.

-leaking injectors. You can pull up the fuel rails, pressure the fuel system (do not try to start) and look for drips.

-weak check valve in the fuel pump. Hardest one to diagnose, but if you rule out the others, this is all that's left.