170 psi in 1/3/5? 0 psi in #2.

[WakkoSS]

#2 cylinder is 0 psi due to a hole in the piston. Doh. #4 and #6 were somewhere in the 136/140 range. 1/3/5 though were all exactly 170. The car has 47k miles on it, valve springs were replaced with LT1 springs years ago (per the previous owner). Could the cam be wiping?

 

[WakkoSS]

Nobody?

 

[750H.P.V6]

Wakko,

Have you actually verified you have a hole in the piston? Sounds doubtful to me. I'd tell you that you have a blown head gasket. The 170 psi sounds a bit high also but every compression gauge is different. If I was in your shoes I'd pull the heads off and see what's really going on.

Neal

 

[WakkoSS]

I had no milkshake and the crankcase was pressurized (car still ran fairly decently, too) so I definitely think it's a piston hole, but the heads are coming off anyway, so the proof of the pudding will come then. 170 across the board on one side and two different numbers on the other seems weird to me. A wiped cam was suggested to me, but I didn't want to assume that until I heard other opinions and verified the psi myself. Someone else did the compression check.

 

[83ttypecooled]

Hi,
If you had wiped some cam lobes, a situation I haven't heard of on a buick v6, you would still have some sort of residual compression. Zero? How about the companion cylinder, #3? I think, as per the other responder, that you are dealing with a blown head gasket. Did you have a detonation problem?
Good luck!
Dale

 

[QKRNYRS]

If you have, or can borrow, a cylinder leakage tester, that will nail down what the problem is. Valves not sealing, piston, head gasket.... etc... I've seen a completely blown head gasket to the intake valley that was low on compression by like 40 psi, but showed 90% leakage. So you must have something catastrophic going on there. Timing chain jumpped? Valve hung open?

Pat

 

[WakkoSS]

I had some serious detonation. I was making a high speed pass at 22psi when my propane lost pressure. I had audible pinging before shutdown and when I killed the throttle it was too late, smoke pouring out the tailpipe and under the hood. Popped the hood to find oil over everything and the dipstick blown partially out. Car still ran ok, just was missing. Before that, the car ran great.

 

[WakkoSS]

The cam lobe problem, by the way, was the suggestion for the over compression in 1, 3, 5...not the zero compression in 2.

 

[gmpower6]

Hey wakko what slugs are in the motor? I broke a ring land on my TRW's. So it might be that.

Sean

 

[S10xGN]

Pull the intake and check along the inner head-to-block surfaces for extruded gasket material. All three of my "0" psi blown gaskets were visible here.

 

[Steve V]

I don't think a copression test will show a wiped exhaust lobe,somebody correct me if I am wrong.

 

[EightSecV6]

Originally posted by Steve V
I don't think a copression test will show a wiped exhaust lobe,somebody correct me if I am wrong.

That is correct. I would expect to see a blown head gasket into the lifter valley