P0303 Cylinder 3 missfire. HELP!

Hi y'all

I have a buddy who just bought a 1999 XJ. It has about 180k and is clean. He's been driving it for a couple months and just the other day it started running rough, and threw a P0303 code. The engine ran fine and quiet, had the normal 4.0 #6 wrist pin rattle, but thats it. It started running rough and pulled the code. Any ideas on where to start?

Thanks,

Mac
 

Judesign

Caught the Bug
Start with the basics like plugs, wires and ignition. Being a single cylinder it could just be a bad plug or wire hopefully. After that, being that it's a single cylinder, he could do a compression test.
 
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