Re: P0300, P0301, P0306 codes
I fought this same war all summer. Had a professional mechanic working on it with me. Tried EVERYTHING...no dice. Even tried a new ECU. My problem ended up being the valvetrain. I had the head sent to a machine shop and gone over and not a single problem since. My symptoms were identical to yours. I went over ignition, fuel injection, ECU, spark plugs, coil, etc. etc. etc. even had compression checked, etc. Nothing solved the issue so I finally pulled the head and BINGO the valves needed work.
YJ, 2 KJ diesels, ZJ, 2 JKUs, and a WJ
I love Jeeps!