I recently did a compression test on my 2.9 with 133k miles.
The results were as follows:
#1- 173
#2- 185
#3- 180
#4- 180
#5- 181
#6- 182
Only #1 cylinder was tested twice.

Having less than 7% variation between high and low cylinders these numbers seem very good to me.

However, I have read that it is possible to be too high and that high numbers could reflect carbon build up. My Haynes manual does not list optimum compression figures, it only states that it should be > 101 psi.

Any ideas?

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1989 XLT 4x4
5 speed Mitsubishi
2.9L

thats perfectly acceptable yes 1 is a little lower but it isnt something i would worry about at this time if it was in the 160 or lower then i would consider looking into a problem. run it your fine

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Depends on how it's checked. I usually check when the engine is cold and don't mess with the throttle (either because I don't care or the engine isn't in a state to be ran). You can get higher numbers if the engine is warm and throttle is open. But variance is what you're looking for. I wouldn't worry if it was 110PSI as long as the numbers were consistent. If it runs, it runs.

Might be right about carbon build up, I rebuilt a 2.9L and was 175PSI across the board with fresh cylinder walls and brand new heads. My 1993 Tempo gets 130-135PSI with 180K miles on the clock. I would expect more or less similar results on an aged 2.9L, but then again it depends on how the test was done. Could try and Seafoam, but really wouldn't worry much about it unless you think it's contributing to a problem.

Hi,
Thanks for the responses.
The test was run engine warm, all spark plugs removed, coil wire removed.
Cranked for approximately three seconds with wide open throttle.

__________________
1989 XLT 4x4
5 speed Mitsubishi
2.9L