Looking for your expertise. My 92 Z28 TPI runs rough, it's losing power and misfires. Here is what I have done and have not done so far:

1. I connected a fuel pressure gauge and it reads 38 psi. The fuel gauge would fluctuate while driving so I replaced the fuel regulator and it fixed the fluctuation.
2. Fuel pressure does not hold, I turn the key position ON, the fuel pump primes and pressure goes up to 40 but then immediately drops to zero. I pinched the return line and no luck. Another reason why I replaced the fuel pressure regulator. So I replaced the inline check valve and it did not help.
3. I had installed a new fuel pump 3 years ago but it wasn't a AC Delco, I figured putting a new AC Delco would solve the fuel pressure issue, no luck.
4. I installed a new distributor, no change.
5. I found one spark plug to be clogged up pretty bad, looks like it has a mixed of fuel and oil. I replaced the spark plug with another one, no luck.
6. The car used to have long cranks and it would take a long time to start. That seems to be fixed now after replacing the fuel pump.
7. So by now, I've replaced the fuel regulator, fuel pump and one spark plug.

What I haven't done:

1. Check for leaking injectors. I purchased the SouthBay injectors and only put about 3k miles on them.
2. Maybe fouled plugs, or spark issue?
3. I have no codes so I need to perform all tests myself.

Thanks in advance!!

Anyone?

A couple of things off the top of my head:

Misfires are generally ignition related. I'm assuming you replaced all the spark plugs; what about the plug wires? You stated you found one of the plugs oil-fouled; that may be your issue. You'll need to pursue that with a compression test to determine what is causing the fouling of that plug.


Have you tested at all the injectors with a noid light? While they are batch-fired 4 at a time, you need to ascertain that all 8 injectors are getting the signal to fire at each injector.

Thanks,

I have not replaced the spark plugs only that one that was clogged up. The wires only have about 3k miles on them same as the plugs and the injectors. I’ll need to test them out with a noid light.

Good idea on the compression test, didn’t come to mind. Will do that.

I basically replaced a lot of parts when I restored the cars 3 years ago, that’s why I’m struggling. Aside from that spark issue, any input on why it’s not holding fuel pressure?

Thanks

Turns out it was the spark plugs, but not the one that was clogged up. I replaced them all and that fixed the issue.