I have been having this problem of a miss/studdering from idle to about 3000-3500

checked fuel pressure it goes to about 40/42ish but as soon as the pump shuts off it drops to 0 in about 2-3 seconds leaky injector or bad regulator is what I was thinking so i checked that out and pressure tested the rail with injectors installed while out of the car and it holds with no leaky injectors so that means thats good but still loses pressure pack thru the pump???

not really sure what the evap system actually does would it have anything to do with it????
any ideas

 

Regulator - or at least it sure sounds like it ...

 

There is a check valve in the pump that could be leaking. This happened to me, but with out the miss. I think it took longer for my car to bleed down to zero, so if it is leaking bad enough I wouldn't doubt the car would have a miss/studder.

 

As long as the pressure is where its supposed to be when the engine is running, and there are no leaking injectors, and the FPR is working, the sudden loss of pressure on shutdown should not cause misfires. The check valve in the pump only comes into play whan the pump shuts down. Should not affect it when its running. You do have to check the fuel pressure under load (on the road, full throttle/high RPM) to insure the pressure does not drop below 40psi.

The EVAP canister in the driver's rear fender strips hydrocarbon vapor out of the fuel tank vent gasses, adsorbing it on the charcoal particles. The PCM opens the EVAP purge solenoid (bracket on passenger side of intake manifold) to use engine vacuum to pull air through the canister, to remove the HC vapor from the charcoal, mix the vapor with air, and burn the HC vapor/air mixture in the engine. Why do you ask about the EVAP system?

If the canister is saturated with liquid fuel, you could be pulling raw fuel into the engine through the EVAP solenoid, rather than a mixture of fuel vapor and air.

 

i asked about the evap cause I had no idea what it actually did and wondered if the evap purge solinoid or what ever could have gotten stuck and was bleeding the pressure that way

 

EVAP system has nothing to do with the fuel pressure.

 

well I can cross evap off my list

I figured it was either a leaking injector or bad regulator checked the injectors by popping the rail off and turning the key on and no spray so those arnt at fault then I disconnected the fuel lines then tested with compressed air and it held pressure until the regulator started regulating but would hold a steady pressure at about 38ish with no vacuum
some times it does it real bad at idle once it gets hot but fuel pressure is about 40-41 when its running I'll try and figure a way to rig my pressure tester to be able to see it when I'm driving and see what it does

I know with out knowing about the fuel pressure it sounds like wires or something spark related Ive triple checked my wires to make sure they wernt melted or arching they are newer but are a cheap brand so I swapped out the drivers side with some msd's but made absolutely no diff so I did not go after the pass side (wonder why ) has a brand new msd coil I had that for the build I'm doing so I just swapped it with the stock coil no diff

whats weird is it gets better at higher rpm, normally things get worse

I'm at a total loss I'm about to say screw it and just deal with it until my 383 gets put in in a few months but It sounds like the thing id cammin hard and when your at a stoplight people start things and sometimes you just cant play