P0303 Cylinder 3 missfire. HELP!

[Thegreenmachine12]

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]

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.