Hi,

Just wanted to make sure that the procedure I'm using to do a compression test is correct. The FSM is quite vague about it. It does go into great detail about setting everything up, then it says open the throttle fully, turn the key, and get the compression number for that cylinder.

Here's my question. As the engine is cranking, the needle on the compression guage will jump up more and more for each revolution of the engine. After 7 to 10 revolutions, the guage is stable. The instructions that came with my compression guage say to take the measurement after 5 revolutions for each cylinder. Well, after 5 revolutions, I'm in the 120-130psi range. but after 7 to 10 revolutions, I'm in the 170psi range, which is good. So is that right? Do you crank the engine until the needle gets stable and take that reading? How many revolutions of the engine does that normally take? Should it stabilize after 3-5 revolutions or is it normal to take 7-10 revolutions?

Maybe after cleaning everything up and putting the engine back together, the pressure will stabilize after 3 or 5 revolutions (the intake valves and seats had a lot of buildup on them, and I installed new valve stem seals to replace the old ones that were as brittle as can be.)
Thanks.

 

When I did a search, it seemed like lots of people were doing compression tests... nobody has any insight on this?

 

When I did my 3.0 I set the gauge face at an angle that I could see it from behind the wheel as I was cranking and cranked until it stablized which was about 7-8 revs I guess.

 

Thanks.