Thread: Compression Test question

I just performed a compression test on my Sr engine a few days ago. Normal numbers for cylinders are 149-170psi. When I performed the the compression check I am getting 185's-190's. What could the issue be? Does my compression tester maybe need calibration? What could be some other causes of this?

Most likely calibration or the type/brand of tester you are using. If you browse around, pretty much everyone gets different numbers with different brand testers. The main thing to watch for as i was told from the wisemen is the variance between cylinder. +/-5psi between cylinders IIRC. If any of your friends have a different brand of comp tester give it a try. I used a Harbor Freight off brand and a Craftsman and both gave me different numbers by about 10 psi but i was solid across the board 2psi variance max.

was the car warmed up

Is it a de or a det? If its a de, thats right about where it should be according to alldata.

when i did my test on my ve i got 180 accross the board, i heard your suppose to open the throttle body when doin the test but i did not because i didnt read about that until after i did my test, i've done the test on a few cars an all usualy end up reading pretty close to the same #'s as long as the engines good..

Yes , I warmed the car up for about 30 minutes.


Yes, I held the throttle wide open and also disconnected the fuel injectors.

The reason why I am so curious is that This engine has about 190000 miles and I doubt it should be reading that high.....I mean a brand new engine but not this one....

there are some reasons that a engine could run higher compression, or not run, but read higher compression and that could be from carbon build up on the valves, carbon build up on the pistons, it could have carbon caked on there and could be giving you higher compression readings like that.

Let's say the engine was a has high/low compression pistons, would this affect my readings?

"Yes" to your latest question.

Just to hop on this question again could I get a accurate compression reading if I rotate the engine by hand?