So I'm trying to diagnose a bad ring or burned valve. I have done a compression test on all four cylinders and the fourth one just hissed when cranking. There is no colored smoke coming out the exhaust. The plug is wet from gas. Also, when the engineis running it seems gas is getting into the oil. Im thinking about dropping the pan and checking for debris. I also thought about doing a leak down, but need to find a gauge first.

 

Any thoughts advice or things to watch out for? Thank you for your thoughts in advance
-V

 

If I remember correctly, if you do a compression test dry, then after squirting a tbs of oil into the cylinder,
the readings will go up dramatically if the problem is the rings, but not if the problem is the valves.

 

^^^ Do a wet test as cristo suggests.

 

Ill give that a try and see what happens. But, if im getting 0 compression on cyl 4 wouldn't it be pointless to do this test again especially on the 0 reading cylinder?

 

Clearly a broken/burned exhaust valve, with zero compression!

 

Is that sarcasm?

I just hope its within the head and not the block too.
Thank you for the input and if you have any more ideas let me know.

Im going to invest in a leak down gauge and compressor since it costs pretty much the same for the service at a shop.

 

Burned valve, leaks out the exhaust port.
Messed piston/ring leaks thru the crankcase.

 

Thank you, I'll look for that when testing.

 

One question....
Sounds like you are on the right path....
But the gen2 cars often get so much carbon on the valves, they loose compression...
Have you looked or tried to clean them yet? Have seen MANY gen2 cars get towed into my local shop, even 2 in one day, with dead cylinders, zero compression, due to carbon on one cylinder ... Such a common event on the "prince" motors...gotta bring it up...
Now tuned cars DO have piston failures...the stage 3 tunes are too strong for stock internals...the pistions fail in the "skirt" area around the wristpin and the rings...basicly takes out the motor, gouging the block...

 

Oddly enough I had someone do the blast at a mini dealership and the car is stock. I'm heading up to northern tools this afternoon to pick up a leak down gauge. If I have time this afternoon I'll report back. But, it might be til tomorrow. So from what I gather the piston that's being tested has to be at tdc correct? What would be the easiest way to position it?
Thank you all for the valuable info. BTW, anyone from Houston?

 

On the prince motor, NEVER rotate the engine backwards....ONLY forwards...this is to to the vanous (vvt) system.....