1994 Trans Am GT LT1 6-speed:
It's been doing this for as long as I've had the car, I just now have the money to fix it. It drives fine but is only an issue on starting.
When you prime the fuel pump KOEO it jumps to 20psi, gives up then drops immediately back to 0. Our possible culprits are leaky injector(s), bad fuel pump check valve, bad Fuel Pressure Regulator (FPR).
Based on random people's advice, spec pressure at idle is 40psi, and 43psi Wide Open Throttle (WOT). When you pull the vacuum line off while running, it should simulate WOT close enough for testing. The hardcore guys want you drive around with your gauge hooked up...but screw that too sketchy.
So I have conflicting results on FPR diagnosis:
FPR is OK:
Pressure jumps under simulated WOT
43-45psi under simulated WOT
FPR is bad:
SOME gas in vacuum line (not pouring out as people report)
36psi @ idle vacuum attached
34-36psi at 3500 RPM vaccuum attached.
Now most guys who replaced their FPR and fixed it were still able to get it to hold pressure for an hour before it slowly dropped, and were not able to simulate WOT. However, they also reported it running below spec which I am experiencing.
EDIT: I have an aftermarket Cold Air Intake (which I want to convert back to stock soon) but I don't think it should make a difference.
It's been doing this for as long as I've had the car, I just now have the money to fix it. It drives fine but is only an issue on starting.
When you prime the fuel pump KOEO it jumps to 20psi, gives up then drops immediately back to 0. Our possible culprits are leaky injector(s), bad fuel pump check valve, bad Fuel Pressure Regulator (FPR).
Based on random people's advice, spec pressure at idle is 40psi, and 43psi Wide Open Throttle (WOT). When you pull the vacuum line off while running, it should simulate WOT close enough for testing. The hardcore guys want you drive around with your gauge hooked up...but screw that too sketchy.
So I have conflicting results on FPR diagnosis:
FPR is OK:
Pressure jumps under simulated WOT
43-45psi under simulated WOT
FPR is bad:
SOME gas in vacuum line (not pouring out as people report)
36psi @ idle vacuum attached
34-36psi at 3500 RPM vaccuum attached.
Now most guys who replaced their FPR and fixed it were still able to get it to hold pressure for an hour before it slowly dropped, and were not able to simulate WOT. However, they also reported it running below spec which I am experiencing.
EDIT: I have an aftermarket Cold Air Intake (which I want to convert back to stock soon) but I don't think it should make a difference.