I've got a 2000 XJ with a CEL. it's throwing codes PO300 (random misfire), PO304 (cylinder 4 misfire), and PO305 (cylinder 5 misfire), as well as PO432. The oil looks good, coolant levels are fine, no overheating (stays right at 210). Also it starts, runs and drives fine. I haven't dug into yet since I'm at work, but I'm worries that these all point to a cracked head. What are your thoughts?

 

Do you know the condition of your spark plugs? Checking those is often the easiest way to see what's going on in your cylinders during combustion. It doesn't sound bad enough that a plug would be wet but it would be distinctly different from the others if you have a leak into the # 4 or 5 cylinders.

 

I'm going to pull them when I get home. I think I might have just freaked myself out a little bit, overthinking it at first. I'll probably swap plugs and the coil pack this weekend, and then see if that clears the PO300 codes. Then I'll deal with the cat issue.