Misfire cylinder #6

[WaXJ_Skier]

Ive been dealing with this for about 2.5 weeks now and I'm ready to ask for help. This all started last time I went wheeling. My muffler was semi damaged to begin with and I intended to replace it soon anyway so bashing it on a log didn't bother me too much. The XJ was loud on the way home I assumed it was the fatty hole in the muffler. I had a noticable loss of power. I replaced it with a Flomaster 40 series a couple days later and I was still running extremely rough. I repleced Cap, rotor, plugs and wires a few days later which helped a lot. Now it only misses when in 4th and 5th gear mostly. The lack of power and vibration caused by this bothers me on the freeway so I double checked my sparkplug gaps yesterday. reset the few that were off a small bit(all @ .035). What bothers me is the #6 sparkplug, it's completely black 10x more than the others and blacker than the ones I replaced and this is all in less than 2 weeks of use. So i'm going to assume cylinder #6 is where the misfire is coming from. Any suggestions/errors in my thought process etc?

1992 HO 185,000 miles

 

[RichP]

Injector, swap 5 and 6, use new o rings too.. Also do a compression test on the engine, post results.