Manifold gasket failure?

[eaglescout526]

Eagle has developed an issue to where cyl 5 is not firing at idle and while cold. But seems to fire when warm and under higher RPMS.

258ci or 4.2L for anyone about to ask. 
 

89MJ and I have been going back and forth on this since I discovered the issue a couple nights ago. We are now to the point where we think its the manifold gasket that has failed at cylinder 5, I found the bolts at 5E, 5I and 6I loose(I=intake E=Exhaust). Made somewhat of a difference but not noticeable enough to be pleased with such. I can tell its been serviced as it has one of those full modern gaskets like what you would find for a 4.0 vs the original gasket that seals the intake only.

 

Can the gasket get worn out to the point where it will no longer seal correctly at a single cylinder? Trying to confirm a theory. 

 

Otherwise, from what I can tell, 5 has compression and spark. My compression tester set doesnt fit the head and so I cant confirm how good the compression is. Though it would tell me the condition of everything that makes that cylinder run. But I have had nothing but issues with that full gasket style even on my 4cyls. 

 

For your viewing pleasure, here’s what the spark plug looked like on 5 prior to cleaning:

 

I think it looks like this because of the valve cover leaking oil and seeping down the manifold gasket and the intake sucking the oil in and basically creating this mess.

 

[eaglescout526]

Bump because I made this post last night.

[derf]

Could be a head gasket.  That's a lot of carbon buildup.

 

I'm doing the intake and exhaust on the 258 in my CJ.  I did the Fel-Pro gasket set.  The main gasket goes on first, then loosely bolt up the exhaust only bolts. The two top center and the two at either end.  Put the second part of the gasket in place and be sure it goes on the alignment dowels.  Then the intake.  Maybe start the lower bolts first.  Then the upper bolts.  Torque to spec (23 ft-lbs for the CJ) in a circular pattern inside out.

 

I left out the second (intake only) gasket and had a gap.  The other gasket looks to have sealed it up pretty good.