[jpd1899]

I need some help interpreting these compression test results. I have a AMC 258 4.2L, in a 1978 CJ7. I did a dry compression test today trying to determine if I have a leaking rings, valves, etc. The engine was cold. I can't keep it running long enough to heat up the block. Here are the results-

1st Cylinder (Closest to the radiator)-150 PSI
2nd-70 psi (dry)--85 psi (wet)
3rd-90/110/120 (1st needle jump/2nd needle jump/etc)
4th-60/90/100/119
5th-90/120/140
6th-150

Cany anybody give me an idea of what may be going on. If its a possibility are multiple things (leaking valves OR worn rings OR cracked cylinder OR etc) what to try to rule them out.

Ultimately what I am want to know is am I looking at a deep tune up or a complete rebuild/replacement?

[mrosseker]

I'm pretty sure your valves are not the problem. If a valve doesn't seat, the cylinder won't progressively build pressure. It'll stay the same, and be quite low. I'm guessing you're leaking past the rings, and they're sealing better as the fuel mixture settles on the rings. If you let it dry out for a while and test it, and the numbers are the same, I'd think that's what's happening. You could also squirt a little oil into the spark plug hole, and it'll temporarily seal the rings and your compression will go up.

Also, what kind of shape were the plugs in when they came out? Fouled, covered in oil, burned, smell like gas? Check them with a reference guide, they can help to figure out what was going on in that cylinder.

You should do a cylinder leakage test. If you've never heard of it, it involves using compressed air to pressurize the cylinders to determine where the leakage is coming from. You'll need a compressor, a cylinder leakage test hose (a piece of airline hose with a fitting the same size as your spark plug hole on one end, and an air chuck for an air line on the other. Shouldn't be tough to find one, call your local auto parts stores.), and some form of regulating the air pressure.
Pull out all of the spark plugs, remove the rad cap, oil dip stick, and air cleaner. Pressurize one cylinder at a time, starting slowly. It shouldn't be necessary to go above 25 p.s.i., which is where the regulator is needed. Listen for the air leaking, and it'll point you in the right direction. If it comes from the dip stick or the P.C.V. system, your rings or cylinder walls are shot, or there may be a crack into an oil passage. If it comes out of the intake or exhaust, your valves or seats are the problem. If it pressurizes the cooling system, or the coolant level rises, it's a head gasket or crack into a water jacket. And if air comes from another spark plug hole (adjacent cylinder), you've got a head gasket or cracked block/head.