Someone wrote -
I did a compresion test and found -- #1-100 psi; #2-130; #3-95; #4-120.
Rob's Response -
Okay -- that tells a lot about the condition of the engine. 120-130 is fine, but 100 and below is not so good. So you have to find our WHY those cylinders are down on pressure. If the poor cylinders were both on one side, I'd lay odd on a head problem, but with one on each side being low...read on.
Try doing the test again on those cylinders (engine cold) and note the pressure carefully. Then squirt about 10cc of engine oil into each plug hole (test one cylinder at time) and do the compression test again. If the pressure now increases a little, it's probably worn rings/cylinders. If the pressure doesn't alter, then it's a valve/head problem. The oil helps seal worn rings s little, but does NOT help burned/tight valves or leaking heads -- so this simple test can sometimes tell you where the problem lies.
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Last revised 4 May 2004.