Weird compression test results 2000 986 S
 

Can’t make out what it could be, The needle on the gauge does not move when cranking but when you push air into the cylinder, it holds pressure and you can’t hear it leak out of the exhaust or throttle body. Took the oil cap off, no noise anywhere. Cyl #1 misfire on obd II. Changed coil and plug, nothing. Engine shakes badly, very down on power, raw fuel smell from exhaust. Quit working under light load at 2000 rpm, just cruising. I’m lost, any ideas???

How are you pushing air into the cylinder? Are you using a leakdown tester? If yes, does the needle move THEN?


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I used a tire fill rigged to the same hose of the compression tester. The tire fill gauge goes up to 100 psi and no air escapes out the exhaust or through the intake. Not a leak down check per say but i think it would be similar in nature. Ready to call it dead, unless someone can help me figure it out.

I've seen this once before, on a pushrod V8. I don't know why it wouldn't be plausible here as well. That motor had a broken valve spring, so when the motor was cranked, no compression. When air was introduced at 100psi, it was enough to slap the valve up into place and hold it there. I surmised then that this is one reason why a leakdown tester has a valve that allows one to introduce air more gradually.

If I were you, I'd get a borescope in there and have a look around.

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