DoctorD415

alright so i've been having some trouble with this one cylinder since i got my 85 GT. The spark plug has been fouling up and causing the cylinder to not fire. There has been some smoke coming out the tails and the color was showing signs of both a little water and oil foul. I took off the vavle covers first and saw that the rockers were all working and whatnot, and then i changed the intake manifold gasket, both because of mabey some water foul and because it needed it, but i still got the smoke. I then decided taht acompression check would be the next best option, figuring that cylinder would be much less and that mabey a head gasket was at fault or mabey a piston ring worn out. So i did a compression check and they all came out the same, would this eliminate both those? Where do i go from here?

kilgorq

Was the engine Hot or Cold when you did your compression test?

Try both ways. Also post your compression summary here. Also post a picture of the plug so we can see what it looks like. It sounds like you have a head gasket issue but I would swear by it. Compression test is a good direction to go, but if you have a head gasket issue or a craked head it may not show up.

capri debris

If the compresssion is equal or close toequal in all cylinders, then it's not the rings. My guess would be that the valve stem seal is bad in that cylinder. You can change them while the heads are on the car... you just have to make sure the piston is in the TDC position on the cylinder you're working on so the valve can't drop down in when you remove the spring. A bad head gasket is possible, but not probable.

DoctorD415

I got a compression of around 125 - 135 in all cylinders. This normal for a stock 302? The first few were when the engine was hot and they seemed a bit lower than the ones i did when the engine was cold, but overall that was therange. I wasnt able to get an actual picture of the bad spark plug yet, but i just put a little description on a picture of a good one to let you know details on the plug. Ill try and put an actual pic up when i get a chance. I think im leaning towardsa head gasket also. With compession all around the same numbers though, this would for the most part eliminate worn piston rings correct? What else could it pretty much eliminate and what do you think i should do next? Is there anything i can do to narrow it down further, before taking a head off.

[IMG]local://upfiles/76165/9E42DB287D81444BA2FBBB009E324E65.jpg[/IMG]

DoctorD415

had some trouble with the picture on that page, but here is it.

[IMG]local://upfiles/76165/0A3DA67791F945BDAA768B881D6A8ED9.jpg[/IMG]

mjr46

Wrong, just because the compression is good doesn't mean the rings are good....remember if you are getting water/coolant in the cumbustion chamber it will not foul a plug...it'll normally wash the cylinder and all carbon away clean.....anyway back to the ring issue.....all a compression test will tell you is that the compression rings are sealing....it does not test the oil control rings which are under the compression rings....which could be carboned/ gummed up and or have weak tension ..allowing oil to slip past fowling the plug.....if the plug is fouled....is it fowled up with black soot or hard black crusty material = oil fouled you may have leaky valve seals which would be evident after letting the car sit and starting it in the morning and seeing a cloud of blue smoke upon start up.......

DoctorD415

alright, thanks for all the info. This problems frustrating me because i keep failingemissionsbecause of it and cant get a sticker, but we'll figure it out.

mjr46

what does it fail for?? HC, NOX, CO...........

kilgorq

A black and dry plug points to an ignition system problems. The cylinder it running too rich or loosing spark.
A black and wet plug points to oil issues. Rings or Valve seals. (Compression is good I would suspect valves seals)

Black smoke is rich.
Blue smoke is oil.
White Smoke is water.

From your description of the spark plug you are loosing spark to that cylinder. Plug wires cap and rotor.

Gary H

Might also have worn guides. Is it CFI or carbed? BTW, put a little oil in each cylinder before the compression test, that will tell you if there's a ring problem.