apyah

Hello, I have a 96 z28 automatic 80,000 miles. last week I noticed the car hard to start. took three tries before starting but ran fine. I was hoping not the fuel pump. last night I put pressure gauge on it and it would prime to roughly 20 psi then bleed down. running it is only at like 35 psi. so i took off the regulator and replaced it. injectors appeared dry but I did not test if they leaked not sure how to. anyways put it back together but still bleeds down just not as much and car starts on first crank even next morning. I will do fuel filter today. but my question would be that I see 40 psi running should be the norm but I run in the mid 30,s does anything change this. I have cold air kit , headers(shortys), hypertech power programmer, lt4 knock module . I am afraid its going to be the pump and I wont pay to have that done if thats the case I will have to do it myself, other than that the car runs great. any advice would be nice. thank you Allen

should add leaked down just slower with new regulator.

BUBBA

Well, usual pressure is 43-45 with vac line disconnected and about 8 less with line connected. The hard starting could be a symptom of FP getting ready to expire. Even with bleed down, when ignition on, the FP should prime for starting. Hopefully someone here can tell you how to check your FP condition. Try a search. JMHO

apyah

I did not have vacuum line off when checking fuel pressure I must have missed where it said to do that, that will make pressure correct if it should be 8psi lower with line connected.

Granite00

It's still a good possibility your problem is a fuel pump. There is a valve in the pump that keeps fuel pressure for a little while. Usually about 5 minutes. If your system bleeds down right away, your fuel lines will be full of air. On the next start, the fuel pump has to purge all the air out, or the engine is trying to run on air at first. They won't hold pressure indefinitly, but they should hold some pressure for a short time.

Also, as the pump gets older they loose efficiency. They can produce good pressure, but the volume will be less. When you accelerate hard, the demand for fuel goes way up, that's why the fuel pressure regulator kicks the pressure up under high load. If the pump is border line, you will have some stumbling on hard accel and long crank time.