My first XJ and first post to NAXJA (Long post)

[XJ-ARNIE]

Nope. Cat and o2 are related to all 6, your miss would be random or on all 6.

I'm of the opinion the compression is low, but not bad enough as well, however, it may be worth your time to preform a wet compression test on that cylinder and isolate the cause of the low compression.

I'm pretty sure you said you did a leak down, where did you hear the air pressure escaping? This is my favorite way to isolate low compression issues. Listen in the throttle, the tailpipe and the valve cover (or dipstick tube)

It's no coincidence that your low compression and your miss live on the same bucket, stay on track, and don't let it get to you. Sooner or later, through deductive reasoning you will find it.

Can you verify that EVERY time you press on that injector, your miss goes away?

 

[evan1395]

Misfire is GONE!!!
I threw half a can of seafoam in the crankcase, drove it around 300 miles, did my oil change with with GTX high mileage and a 16 oz can of Engine Restore. As i was draining my oil I kept hearing "plops" into the oil catch pan below. Drove around about 5 miles after the oil change and was really brining the RPM's up through every gear. My check engine light just shut off and the misfire is gone. Its been about 150 miles now and still no CEL or a single misfire. Not sure if it was the seafoam or the Engine Restore. But either way, im happy

 

[evan1395]

My guess is the valve was gummed up, and the "plops" i kept hearing drop out of the drain hole were sludge deposits that the seafoam helped loosen up?
Cant wait to do another compression test and see if that can of Engine Restore brought the compression back up in cylinder 1.