Anyone know how to diagnose and pinpoint which fuel injector is losing pressure if there's no misfire?

My Maxima's fuel pressure drops to 0 psi within a half a minute after turning the vehicle off. Stupid thing is I thought it was the fuel pump so I replaced it already and of course it still does it. I capped the line going to the fuel rail so I could test the pump and it holds much, much better than uncapped so I want to say the fuel pump is good. The FPR has no fuel in the vacuum line so I assume that is good as well. For some reason I can't even find the damper so...heh...

I'm assuming it's an injector or o-ring...any way to tell which one(s) exactly without taking the rails out?

 

You can attempt to remove ignition coils and turn key to ON position and remove spark plugs to see which one is wet and smell of gas.

 

Ya, I was thinkin that...I'll give it a shot!

 

Well, I ended up taking both fuel rails off the manifold and pressurizing them from the fuel pump...none are leaking. I'm now thinking the fpr is somehow allowing fuel to flow back into the tank via the return line. Pressure is good with and without vacuum....I never really studied the insides of a fpr, but I assume it's something like a valve or diaphragm that obviously controls pressure. Now is it possible it's stuck at a certain angle where the pressure when the car is on is still within spec, but when the pump turns off the valve is still stuck open or something?

 

ok, well i plugged up the return line after the fpr and it's holding much better...looks like that's solved...guess working pressure isn't a full diagnostic after all...learn something new every day..

 

Which means your FPR needs replacing which should also indicate that during winter, your car starts and then cuts off correct?

 

Is there a problem with the engine that's making you look at FPR values after the engine is turned off?

 

hmm, haven't had the car that long...

 

random hard start/long cranks.

 

The hard start is random, but the fuel pressure fall off happens every time the car is turned off? Does the pump prime correctly when the key is turned on?
Don't concern yourself with the pressure fall off, check for an initial prime as you start.
Fact is most systems bleed down to zero over time, don't chase that, just verify you get pressure when you attempt to start.