4.3 W/ Zero Compression...HELP!!!!!
 

OK here is a good one for all you gear heads out there...

The culprit- 1999 Chevrolet Silverado (new body) w/ 4.3 liter V-6

The issue - Zero compression on #1 Cylinder - All 5 other cylinders are within 1 PSI of 165 LBS.

Scenario - I checked and rechecked the compression after buying this truck with a really bad miss. Like it says above #1 cylinder is the issue. I have pumped air into the cylinder and could not hear it through the exhaust or throttle body thus theoretically eliminating a valve issue. I already had the valve cover off at this point and observed both rocker arms moving through the same motion as the others. So I assume it was a ring or head gasket issue and removed the head. The gasket appears to be intact with no obvious breakage. The piston doesn't have any cracks or in this case with zero compression a huge hole. I then remove the valve springs from the intake and exhaust to check for a broken one and they were both fine. So then I flipped the head over and filled the combustion chamber with denatured alcohol to see if maybe I missed the leak with the air being pumped in. It held the alcohol with zero loss after an hour. Now with the head removed I turned the motor over to check the cylinder walls and to make sure the piston was moving up and down. Everything checked out fine. I then brought the piston down as low in the cylinder as possible and filled the cylinder with alcohol to see if I had a ring issue. It too held perfectly. I also checked to make sure the lifter were moving up and down and they are, just like the others.

What am I missing???? Could the hydraulic lifters some how not allow the valves to close fully with the motor cranking and running???? I am at a total loss of ideas here.

HELP!!!!!!

I may be way off here but it seems like the problem maybe only occurs when the cylinder is under pressure. As much as I hate to suggest that you throw parts at it, you've already got it torn apart, might as well replace the head gasket and rings??? It's a guess but even though it holds the fluid, that doesn't necessarily mean it'll hold up under any kind of pressure. Is there a test you can do with the head off, applying pressure into the cylinder???

I am thinking along the same lines, not so much the rings, but the lifters. I think they may not be allowing the valves to fully close when running or cranking. I am going to take the head to the machine shop on Monday for them to test it. If they don't find anything I think I am going to buy 2 new lifters and put it back together like that. In my opinion that is all that is left. If anyone can think of something else let me know.

Bolt the head and gasket on another motor???

What kind of lifters does that motor have?? Roller or hydraulic??

They are hydraulic roller lifters.

Get the heads checked at a machine shop where they magnaflux them. Other than that, I would have to say what you are thinking, a bad lifter.

Yeah thats the plan. I should know something tomorrow. I will post my results.

Well the head checked out fine...I guess I pulled it for no reason (besides practice)! I hate it when that happens. The guy at the machine shop suggested I pull the piston out and inspect it. I just don't see a ring messing up and A: There is no scaring of the cylinder wall and B: It holds fluid during a leak down check. I went ahead and had the guy clean the valves and head up for $50 so I all I have to do is clean the block and stick it back on. If the rings hold fluid than they should make some compression even if it is low (in my opinion). I think I am going to put 2 new lifters in and put her back together. If it runs - great, if not you'll see it on eBay in the parts vehicles section. This is definitely a first for me!!!!!

Dam man!!! Sorry to hear that. Its frustrating I know. But maybe later the bug will surface. Im stumped myself.