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

 

Fuel in oil is likely caused by a leaky injector. Fuel is much, much more vicious than oil so it can easily seep by the rings.

 

So should I look at my injectors first, before my piston rings? How Do I Check The injectors?

 

injectors leaking or not flowing the same, plugs (make sure they are all good and firing), fuel pressure to high. best way to check injectors is the take em out and have them cleaned and flow tested at an injector shop. i tested mine for leaking by taking the injector rack off with injectors connected and cycled the fuel pump by turning key on and off to bring pressure up. also placed pieces of card board under injectors to show if fuel was coming out.

 

You can check for leakage by using a fuel pressure gauge on the fuel rail fitting. Turn on the key to get the pressure up to about 40-50 psi and wait to see how fast it leaks down after the pump stops. More than a few psi per minute is not good. Leakage indicated is not always caused by the injectors, but if they are leaking, that will show it. To find out which one is leaking, you have to pull them up and repeat the process while watching.

 

You should really get the whole "I have gas in my oil so my rings are bad" out of you mind. Bad rings do not cause that. When gas and air enter the cylinder the fuel is a vapor. There are two things that can happen once the air/vapor mix enters the cylinder.

One it fires, the gas is all burnt It takes a lot of pressure to blow by even a worn out rings the only thing getting passed a worn ring is exhaust gas not raw fuel.

Two it does not fire. In that case you have a dead miss in the car and the air and vapor do not generate enough pressure to blow past the ring and the air/gas just goes out the exhaust valve.

I have worked on cars that the rings where so bad they would just blow out the valve cover gaskets as soon as the car would start it would puke oil into the air intake cause smoke out of the tail pipe. No gas in the oil.

I have works on 100's of cars with misses, no gas in the oil.

I have worked on cars with gas in the oil and you need to be carful and get that out of the engine asap. I have seen valve covers blown off motors before. I have seen three reasons for gas in the oil, An old school mechanical fuel pump with a cracked diaphragm ( your car does not have one), a stuck float on a carburetor ( no carb on yours either) on a car with a aftermarket electric fuel pump and a leaking fuel injector.