#2 compression went to zero

Post by **erikv11** » 04 Jul 2011, 22:14

OK, maybe it is 10, not zero, but what's the difference.

See this thread - been running a 100k junkyard engine for a few days now. It has been running very smoothly, up to about 150 miles now since I started it. Still on the first fillup of dino oil, 10w-30. So I am sitting at a stop light a few blocks from home tonight, car starts running rough. Chug it home, CEL comes on, P0302.

Fearing the worst I immediately go to my compression gauge. #2 gives me almost no reading.

two days ago: 200-210-190-180-205
two hours ago: 205- 10-195-200-205

There was no blue smoke last 100 miles, no smoke at all in fact. Somebody please tell me this is just carbon, and not a burned valve, and more importantly how I might quickly figure that out without pulling the head. Maybe I need to get ahold of a camera.

Post by **jblackburn** » 05 Jul 2011, 06:01

It could just be a stuck valve/lifter.

Drive around for 3-5 minutes in a low gear above 4000 RPM and see if it frees up.

Post by **erikv11** » 05 Jul 2011, 08:41

OK that didn't change it, any other thoughts?

Post by **FlyingVolvo** » 05 Jul 2011, 08:52

The fact that all of them are okay, except one is not good... If they all had low compression, then maybe the sticky lifters would be to blame. But since you had good compression just a couple days ago, I'd say this is not good news.

Post by **vjaneczko** » 05 Jul 2011, 09:31

Did you run SeaFoam through it? I didn't see if you had in the other thread.

The oil you have; does it have any cleaners or stuff for high-mileage engines? If not, I'd change it to something with additives. Hopefully jblackburn is right...

Post by **jblackburn** » 05 Jul 2011, 09:43

Stick your hand on the exhaust pipe as its running (and the exhaust is cool

). If you feel it sucking in, there is a burnt exhaust valve.

You can also bring the #2 cylinder to top dead position (by rotating the crank around) and use an air hose/compression tester fitting. Listen for air out the exhaust.

Post by **erikv11** » 05 Jul 2011, 10:36

OK, I can do the leakdown test after lunch.

But will that distinguish between a stuck valve and a burnt valve?

Post by **boosted5cyl** » 05 Jul 2011, 10:37

Jblackburn made some good suggestions, although rather than using your hand for the exhaust test, use a piece of cardboard. Or bring it to TDC on the compression stroke and get some compressed air in there. You dont even need a leakdown, just listen to where the air is getting out.

In terms of checking weather its stuck or burnt you can....

Try and get a borescope in there
Pull the cam cover off and take a look
Remove the exhaust manifold, take a peek

Might well be better ideas out there, these are off the top of my head.

Post by **jblackburn** » 05 Jul 2011, 10:44

I just re-read your initial post, and two things make me think lifter:
1) It sat for a long time and made lots of noise at startup.
2) It's not dead "zero" compression.

In terms of diagnosing stuck/burnt valve:

https://www.matthewsvolvosite.com/forums ... =1&t=30063

http://www.pistonheads.com/gassing/topi ... e%20please

Since the high-RPM driving seems not to have helped it, the Seafoam or AutoRX might clean up some gunk on the valve stem that might be keeping it from closing.

If all else fails, you'll probably have to resort to yanking the head to find out for sure.

Post by **boosted5cyl** » 05 Jul 2011, 10:49

If you suspect a stuck lifter, pull the cam cover off, check it and maybe replace it. They are cheap enough and easy to do. I guess you could hit up the timing belt replacement at the same time if it happens to be due.