Questions Regarding My Compression Test

[cmjdskates]

I preformed a compression test yesterday and got (from left to right) 178, 178, 163, 178psi. I have a 96 gsx so 178psi is what it should be, but why do I have 163psi in that one cylinder and what could I/should I do about it? Thanks for the help.
Chris

 

[diablos991]

Usually a difference of that stature between cylenders is a sign of a bad Head Gasket. Did you perform a wet test?
What prompted you to do this compression test? Any smoking/leaking? If so let us know so that we can better help you.

 

[Big Woo]

Was the engine warm when you ran the test?

Generally speaking you don't want to see more than a 10psi swing between cylinders. There could be alot of factors involved here, such as number of compression cycles per cylinder during the test, throttle position, engine temp. Or it may be the start of a bigger problem, like a ring sealing issue, or a valve seat problem.

Before doing anything I would prefom the test again, with the engine warm, good battery voltage, throttle open and equal compression pulses for each cylinder. If you still get a low value on #2 cylinder (asumming your left to right as you were viewing the engine) add a couple of squirts of oil to the cylinder and retest, see if the pressure value increases by 10 psi or more.

For a more accruate test try a cylinder leak down test to verify where the leak is comming from and how big it is.

 

[cmjdskates]

I preformed the test because while I was tuning with dsmlink I tried to push to far. Started loosing power. That turned out to simply be a combination of boost leak and blowing the boost source hose off the fpr (caused a "fuel trim malfunction" code). Before I figured that out I assumed I did some serious damage.
I don't have oil and coolant mixing and I do blow a bit of smoke under WOT but it's a dsm so if I wasn't burning a bit of oil...well that would scare me. Smoke is not white. Haven't done a wet test yet. That just entails a cap full of oil in the bad cylinder, wait ten min. and test the cylinder again??? Is there more to it then that? And oil in the cylinder, this is ok to do and not clean it up? Just let it burn off while driving?

 

[TSIfreek]

What do the plugs look like? Any tips melted??

 

[cmjdskates]

No, the plugs are cool. Just put them in on Sat. along with new wires Sun.

 

[Dark_Horse]

Haven't done a wet test yet. That just entails a cap full of oil in the bad cylinder, wait ten min. and test the cylinder again??? Is there more to it then that? And oil in the cylinder, this is ok to do and not clean it up? Just let it burn off while driving?

It's just fine to leave the oil in there. It will work it's way out once you start the car up again and you'll have a bit of extra smoke for a few miles from it. But it doesn't do any harm so long as you don't use too much oil.