Discussion Engine compression test

[Knox7095]

So I finally got around to doing a compression test. Did them cold and hot as well as throttle open, closed and only 4 puffs (compression strokes) The results are cylinder 1 .. 160 , 2 .. 165 , 3 .. 165 , 4 .. 165 .. seems good to me of course this is just the top of the motor. Oil pressure test next. Also seen no reason to do a wet compression test .. sorry I haven't been on here in a wile broke my phone. 2000 grand am 2.4 l ...... 276,547 miles

Yea no obvious blow by, like maybe a little steam by removing the 710 cap, but that's more than likely hot oil. The only real reason I was doing this is it still has a random miss at random times .. mainly at idle and I seen smoke one night. Someone peed me off and rode my butt like a whore in church so I floored it she when to 5800 rpm and there was some type of something that came out the back to be fair it was a fair amount. Not at all sure. When I did the compression test I only did four puffs no more or less. So the compression is really like 170 or 180 if you let it go 6 or 8 strokes. I don't know the max psi there. I'll deffo be gitten back to do a re-re-re-test.


Ok well re did test to see max pressure.. after 7 or 8 puffs it came out to 180, 185, 185, 185... and it stayed there even if you did ten puffs

 

[JCH13]

Do a leakdown test if you want to know if things are okay or not. A compression test can be influenced by starter and battery health and if you have the other spark plugs installed. 170-180psi sounds healthy, especially given the mileage, but those numbers are not especially useful if you don't know what the FSM sets the threshold at. I've seen numbers range from 135-205psi depending on the engine. I don't think it's worth anything to retest compression at this point.

To hazard a guess I suspect that you're leaking some oil past your valve guide seals and maybe have a sub-par PCV system. Extra oil in the cylinders will result in some fun smoke, would let your compression test look super good despite the high miles, and can lead to fouling of plugs or general not running super nice.


Having said that, if you don't regularly let the go pedal meet the firewall it is not surprising that some shit built up and kicked out when you floored it. I notice the same thing with my MR2 that has leaking valve guide seals.

 

[Knox7095]

What is FSM ??

JCH 13 thanks for the input

It burns about one quart every 2.5 to 3k and use full synthetic high mileage oil of 5w30

No all the sparks where out when I did both tests, engine was hot then cold same readings. I'm sure plus/minus 1 .... I think it is the PVC system. It uses an air-oil separator instead of PVC valve. No the sparks don't really foul out. I drive mainly highway sometimes 75-80 mph for extended times. Another thing off topic is at 80 mph the rpms w torque lock up on cranks 2475-2500 RPMs so when I hit the petal it jumps to 4200 to 4600 ishikawa (<--- that's spell checked haha) I looked at the crowns as best as I can and see that there not real dirty to say, can see some writing, now you know that means I can't see the valves or even the whole cylinder though....

 

[olds]

Factory Service Manual

 

[Knox7095]

Factory Service Manual

Damn I was in the army I should have know haha