Odd compression. Rings? Valves? Both?

[SonySlave]

So I broke something at the track last Saturday. The car was running great all day long. The car ran a best to date 12.2@114 and 12.2@117 (thanks to Brummellz). I was ecstatic! Then on my last run, during the 3-4 shift, the car started shuttering really bad. The motor was missing really badly. My friend Lucas was thinking I burned another valve just like I did last summer. So I packed up and drove it home.

I pulled the plugs first to check them. Plugs 2-4 were all intact and dry with regular carbon buildup on them and no peppering. Plug 1 was also intact, but had oil on the lower half of the threads near the electrode. Also, oil had kind of seeped out from cyl. 1 between the head and exhaust manifold. I looked onto the piston tops and #1 was wet. I also pulled the exhaust manifold off and there was oil around the #1 port area.

So I did a compression test. It was a cold test, which I know reads lower, but better than nothing. Cylinder 2 had 125psi cold, cylinder 3 had 130psi cold, cylinder 4 had 75psi cold, and cylinder 1 had 10psi cold. So I added a capful of oil to #4 and it jumped to 135psi. Added a capful to #1 and it made no difference at all. Still 10psi.

I'm a little confused about the 10psi compression. Last year when I burned a valve, there was 0 compression, I mean NONE! But now the gauge definitely jumps right to 10psi. So I'm starting to wonder about things. I don't have access to a leakdown tester, so obviously I'll need to pull the head to check the valves, but I'm more concerned about the motor itself. The head was rebuilt last summer because of a burnt valve, but the bottom end has 138k original miles on it. I really wouldn't be surprised if something in the bottom end is bad, possibly the rings, due to the oil coming out of the #1 runner. However, the car doesn't smoke at all. I don't know...

Any ideas or recommendations?

 

[Boost92awd]

You should really try to find someone that will let you borrow a leak down test. Maybe go on your local DSM forum and ask around there. A compression test is really hard to pin point whats wrong.

 

[assault187]

You should warm the car up to operating temps to do a compression test, If the compression raises with oil in the cylinders its a ring problem, if it make no difference then its a valve, or HG problem. Then you move on to the Leakdown test to troubleshoot further.

 

[Big Woo]

warming your car up will not increase the compression numbers from 10 to 130+.

Seeing 25 psi or less is not unusual, the cranking compression psi value is dependent on many things. You burnt or bent something.

Since you saw 0 psi last year, and this year you see 10 psi, just means you did not bent or burn something quite as bad as last time. I.E. a little smaller hole allowed some amount of cranking psi to be developed.

Since #4 jumped up with oil added, that generally means you have a pistons ring issue in cylinder #4. With number #1 you get 0 both ways, means the leak is bigger than a little oil can mask momentarily.