I have a 99 xj 4.0. It recently started badly miss firing under load. I’m stuck on why to do. I’ve done a complete tune up, tps, and an upstream o2. Checked grounds and everything. Not sure what to do next. Any ideas?

 

You did plugs and wires ? Cap and rotor ? Verified spark to each cylinder with a spark tester ? Compression check ? When asking for help always try to include as much information on the issue at hand as possible .

 

Is the CEL on or flashing when this happens? A misfire usually throws a code. Even with no CEL, i would still look for any stored codes.