Need some advise please..low compression #3
 

I have a 2006 Express 2500 with 6L and about 225k miles. Engine code was random misfire. Ran great off idle but stumbled noticeably when idling. Checked with scanner and found #3 cyl. was culprit. Did compression check and found it was way low...like 80# compared to ~165# in others. Squirted oil into cyl. and retested with same reading.

I thought it might be a bad exhaust valve so I pulled head. I removed the valves and I can't see any damage or indication that either of the valves are the problem. Also, I can't see where the head gasket may have failed. Intuition now says compression ring? The cylinder looks and feels good with no irregularities. I was even surprised that the ridge at the top of the cylinder is almost undetectable. This engine has been very well maintained I might add.

I'm thinking I can do 2 things now;
1. pull the oil pan and remove the piston to inspect. This job doesnt look to bad at 1st glance but... I've never done it before on a van or an LS engine. It does look like there is enough room between the cross member to get it off in the vehicle but it seems likely there will be some unknown issue removing it.

2. put a new head on and test compression again. A reman head from the parts store is ~$300. The head I have has 2 broken exh. manifold bolts anyway...both outer bolts which I did not do. Not sure how or why, someone may have over-tightened them to stop a leak I suppose.

Is it possible one of the valves is not seating properly and I can't see why? Or am I just subconsiously avoiding the messy, pita job of removing the oil pan, piston, honing the cylinder (which I think would be near impossible in the vehicle given it's location), re-ringing...etc?

Any of you experience LS/Express guys have any thoughts/suggestions?

Thanks in advance.

If you suspect a valve seat issue, I'd put some water in the exhaust port. If the seat is leaking, it will show.

ok, so I got this great idea, brilliantly simple...it goes like this: pour water into the ports and then see if the valve leaks :D

Sure, sure its my idea, ill take credit for the whole thing. Although I feel like there should be a $300 tool for this...

So I checked all exhaust and intake ports. It was grueling. I had to take a 12 oz bottle of water and lift it up to the port. Next I had to use skilled and masterful coordination to manipulate the position of the bottle so that water would pour out at the perfect rate of flow. Timing was critical as the amount of water delivered had to be just perfect. This technique had to repeated 7 more times! I was physically, mentally and emotionally exhausted after this procedure. It took about 360 seconds to complete and I even got my boots a little wet!

I know, the suspense is killing you...

3 of the 4 exhaust ports trickled water ever so slightly, including #3. Only one of the intake ports leaked, #3, and it was like a sieve.

I conclude that the low compression condition in cylinder #3 was caused by a bad intake valve seat. Hmmm, I wonder why though. :confused:

I know, I should have been a writer...right?!

Thanks for your help Kevin! That was so simple that I feel like an idiot.

I'll let you know how things turn out with the new head.