I'm doing a compression test on a 98 z28 and I'm wondering if anybody knows what psi I'm supposed to be looking for. I can find TDC by using my thumb on the plug hole, I just don't know the pressure. The resin why I'm doing a compression check is because I am having fuel in the oil and I'm testing the piston rings for proper seating. Any helpful tips/advice will be helpful

 

Usually 150 PSIG, if 10:1 static compression ratio.
The test you should perform is cylinder leakdown.
Bring piston to TDC, inject a known pressure and read the leakage.
Any value below 10% is good, if lower, add oil to cylinder and retest.
If value improves, bad rings.
If value stays the same, bad gasket sealing or valve seating.

 

i would suspect a leaking injector or failing fuel pressure regulator making fuel pressure to high. if your getting to much fuel to the cylinder or the plug is not firing gas is going to get into the oil. had the problem with a new engine and it was high fuel pressure shooting way to much fuel at low rpms.

 

My vote is leaking injector also and its leaking down overnight. I have worked on a lot of cars with bad and even cracked rings and gas in the oils was not an issue. There are a LOT of other issues that bad rings would cause.