Compression and Misfires. I need help

[jshuman]

Hey everyone,
I recently got my 92 gsx back on the road. It has a manley/mahle 8.5:1 bottom end and a ported 7 bolt head with a bc valve train and stock cams, ARP studs and a cometic head gasket.

I am having a misfire on cylinder 3. It started off slight and intermittent, but now that cylinder is completely dead. I have replaced the plug, wire, and coil pack and have verified that it has spark. I also swapped the injector with a known working injector (I'm running stock 450s).

I did a compression test and cylinders 1,2,4 were 176-178. Cylinder 3 was 147. I know that is low, but I didnt think it was low enough to cause a dead miss. The head was installed and torqued 30,60,90. I was having an oil leak that we couldn't find the source of and after about 500 miles of driving decided to retorque the studs. I had read some posts of people torqueing the arp/cometic combo to 100ft/lbs, so I did that. Then two days later is when the misfire started.

Am I overlooking something, or do I need to pull the head and get a new gasket?

Any input would be considered helpful.
Thanks!

 

[c2ypt1c]

I would definitely consider performing a leak down test:
Leak Down Test VFAQ

You probably already know this but just in case - you could try a quick and dirty compression test of the rings, just for the hell of it, by putting a capfull of oil in that cylinder and see if the compression goes up.

 

[jshuman]

I should have mentioned that I did put a large capful of oil in it. It raised it to about 158. But I am wondering if it was just due to the volume of oil taking up room in the combustion chamber. Also, the car does not smoke at all.

 

[WES_393]

Your correct about the oil. With dished pistons (especially how deep Manley's go) your most likely just increasing the compression ratio. The ideal method would be using a flexible hose attached to an oil can to squirt oil onto the cylinder walls.

However, at this point I wouldn't waste my time with any tricks. I would run a leak down test on that cylinder in order to get an idea of what went wrong before tearing it apart. It could be simple as a pumped-up lifter or serious as a broken ring. Either way, 147psi on a new engine is way too low.

 

[jshuman]

The engine isnt brand new. It has about 5k miles on it. But still I cant stand the thought of 3 being right on and 1 being low. And the fact that there is a miss on that cylinder means I dont have any choice but to fix it.

 

[jshuman]

I pulled the head last night and this issue was definitely with the comedic head gasket. Which really pisses me off since it has less than 200 miles on it and has never seen over 10 psi on a 14b. There was a little "channel" on the front of cylinder three and it left a nice oil path from the combustion chamber to the front of the block about 6mm wide. The head was milled and the block was inspected before the gasket was installed with arps torqued 30,60,90 with moly lube just like every other hg I've done. Put the new gasket on last night, but didn't get everythin put back together. I should be able to post back late tonight with new compression numbers.