Alright, here are the numbers, Im thinking I have a burnt valve or bent push rod or something maybe bent valve, it pops and backfires, alot of valvetrane noise on the passenger side. Not sure what compression should be but here it is.

#1 210
#3 220
#5 200
#7 210

#2 210
#4 180
#6 180
#8 (didnt do it, too hard, tried for an hour) guessing its around 200)

Let me know what anyone thinks of this. Help is appreciated.

 

I don't know they cylinder set up off hand, but I'm thinking if the low compression on 4 & 6 are right next to each other it maybee a problem with the head gasket.... wild guess but easy fix, what is it about 20 bolts to pull and $20 for the gasket or $35 if you redo the plenum

of course it could be a million other things

 

Is it acting funny? What do the plugs look like in those holes. The thing is ten years old, it is not going to be perfect anymore. If there are no issues I wouldn't mess with it.

-Geoff

 

The car was backfiring and popping, when it gets warm or near really hot then it will start popping like a shot gun. Its deffinantly missing really bad during idle and even running and doesnt want to climb RPM's, I have an ongoing thread about it until I fix the problem. Theres alot of valvetrane noise. I had someone come with HPTuners and tune it but there wasnt much the tune actually did. Its a 98 LS1/M6 swapped into a 96 Z28. I have tested everything else, replaced coils, checked timing chain, the only thing left would be a bad head, bad valve(s), bad pushrod(s), or bad lifters. This is why Im running a compression test. Thanks for any input on this.

As far as plugs, all looked normal, some cleaner than others, non burnt up or with anything built up on it. Some were blacker than others, but its just carbon probably from running a little rich or the misfiring that did it.

 

Pull the tappet cover on that side. It's pretty easy, you don't even need to pull the coils. Pull the rockers for the cylinders that you want to check then use your compression tester to put a steady stream of air to the weak cylinders and listen at the tail pipe and tb for hissing to tell whether you have bent valves.

 

sounds easy enough, also Im running headers and y pipe only so it shouldnt be hard to hear the hiss. You mean pull the pushrods correct, because youd have to pull the heads to pull the lifter.

 

I agree, them compression #'s look ok to me, but thats just from what iv seen.
What im saying is I do not think the compression is causeing the issue.

 

From what ive seen, compression is good, the numbers so far. I think I could have an issue with something being bent, maybe even a dead cam?

 

Yeah I meant rockers, not lifters.

 

Not Good.... How many Miles on the engine?