Only 45lbs of compression

[fearnot]

1998 Grand Prix 3800 NA. 130k miles Dad's car.

I'm no mechanic but here's what I have.

Compression - #1 is 45lbs. #3 and #5 are 175lbs.
Leak down at TDC - #1, pressure seems to flow right out the exhaust, At least that's the only place I can hear it from. no leakage into #3, no pressure spike in coolant, no air out the dipstick.

Valve lash on #1 was very similar to the rest, indicating to me that the valve might be fully closed and not hanging on carbon or something. I haven't yet measure the valve stem height or valve guide play though.

If the valve is closed and the pressure soundslike it's comming out of the exhaust, I'm guessing it indicates a burt valve. I don't see how a head gasket could do that, right?

Am I looking at pulling the heads and having them worked? Or is there something else I should be looking at first?

Thanks in advance for any input.

Ian

Some back up info.....
It developed a miss that would come and go. CEL would light solid and go away after time. Most times it would run fine, but occasionally it would develop a miss while at highway speed and it would stay, from idle right on up. The only code was P0300 misfire. Dad tried chasing the problem down with coils, plugs and wires. It was fine for a while, then the miss came back and stayed for good. CEL started blinking, codes are P0300 and P0301 (misfire in Cylinder #1).

Previously, when chasing the problem and changing plugs, they all looked lean. Now they're all lean and #1 is black with gunk.

[richtazz]

I moved your post from the tips and maintenance sub-forum to the regular Grand Prix forums to increase it's visibility.

It sounds to be that you have a bad exhaust valve. It's either bent, burnt or so clogged up with carbon that it can no longer seat and hold conmpression. A bad head gasket will normally cause other issues (coolant in oil, oil blow by, etc...) and not just leak out the exhaust. Repair will require removal of the cylinder head.

[tblake]

fearnot...

It sounds like your on the right track with your diagnosis.

I agree with rich, but you can try one more thing....

Remove the rocker arms for the number on cylinder and do a leakdown test again. This will verify that the valve is closed 100% if its not bent/burnt/carboned up. Also while your there, inspect the valve springs.

[fearnot]

Originally Posted by tblake

fearnot...
.............. Remove the rocker arms for the number on cylinder and do a leakdown test again. ........... Also while your there, inspect the valve springs.

Done and Done.

Ian

[tblake]

and its still leaking out the exhaust? Then your pretty much looking at a new valve job. Sorry man, but hey, its a 3800 so its very easy to take apart and when your done, you'll have taken care of replacing your head and intake gaskets.