what would cause fuel pressure to quickly bleed off in a EFI system? I'm working on a port fuel injected rig, the pressure with key on, goes up toward 30, but bleeds right back to zero when pump shuts off.

when I managage to get it started, it maintains 50 or so PSI. when I turn engine off, it bleeds right back to zero...

regulator or leaky injector.
only 2 options.

forgot.
if you pinch off the fuel hose after it hits 50 psi and it drops (with the car off) it is a leaky injector.

if it is the reg don't worry about it. happens, just makes it hard to start.

does the pump have a one-way check valve of some sort?

I don't know of one that does. mostly it is in the regulator.

thanks for the info!

UPDATE: I clamped the return line closed, and it STILL bleeds off pressure. must be an injector...

well not necesarrily.

depends on how it is setup.

like mine goes pump, regulator with return line to the injectors.

clamping off the return wouldn't prove anything.

dodge trucks do a returnless system, so clamping it off where it feeds the rail would show it is injectors.

I think ford does it where it pumps to the rail then returns off the rail.
in that case you would have to clamp both lines. the return first then the fill line.

What exacty are you working on? Knowing what it is may help with the diagnoisis.

a ford...1987,4.9 L(300 six)

Why dont you pop the rail and injectors out of the intake so you can see what they are doing? With them raised out of the intake, cycle the key, watching if they leak down. Does the engine act like its flooded when trying to restart? That would also be an indication of leaky injectors.

yeah, it is real hard to start...pulling the rail is a real pain on this motor. but it needs to be done. I will see what I find. thanks guys!