Did compression test and average 200psi across all cyl. Is this good or bad?

101,745

Asked by Sep 22, 2012 at 01:32 PM about the 1991 Mitsubishi 3000GT 2 Dr SL Hatchback

Question type: Maintenance & Repair

3L DOV v6 (non turbo).  Compression ratio is 10:1.   Did compression test and average 200 psi across all cyl.  is this
a good or bad psi for this engine?   

4 Answers

101,745

Believe I got the answer. Psi should be 15 to 20 times the c/r for stock engines. If that is correct mine is right at the top of the range. So I am going to take it as a good reading. If anyone knows of any reason this might not be correct please let me know. Thanks

1 out of 1 people think this is helpful.

a few qus for you...how many revolutions did it take? if more than 3-4 then dosen't mean much..each rev should yeild a higher number...You may be able to crank these cylinders enough times to come close to the other cylinder's total PSI, and this is one reason to limit the number of compression strokes. Poor rings usually cause this condition. Be aware that a cylinder suffering from excessive oiling, even from bad rings, can yield high compression test results because the excess oil in the cylinder seals the rings..secondly what was the largest difference between cyclinders...more than 21 pounds generally indicates worn or broken rings, leaky or sticky valves or a combination of all....

101,745

I do all compression tests only eight revolutions per cylinder(I do not advice doing more than that) and with all the plugs out. So that all things are equal. If one has a lower number than the others I add a little oil in that cylinder and redo the test. If number remains lower than others it's probably a valve or head gasket issue. If number increases (to almost where the others are) with oil in cylinder on top of piston then you probably have a ring issue. Have learned a lot about these engines since I asked this question.

1 out of 1 people think this is helpful.

I currently own a 93 mitsubishi 3000 gt/sl/na. one morning went to start it up sputtered and noticed RPM gauge onle going up to 2000 or so. Pulled the upper cam timing covers off to check the marks on the sprocket to head alignment per intake and exhaust marks.front bank was way off and rear was 1 tooth off.what is totally blowing my mind is this car still starts and runs but sluggish at idle. Another thing to point out is my power steering belt has ate all the way through the lower timing cover, possibly causing adjuster or idler pulley damage.hope i havent damaged valves.All you techs out there solve this one,Next is plenum removal and compression check, then line up all the marks, If i still have a problem looks like rebuild. or FOR Sale AS IS. Thanks RWH.

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