It's the crank sensor!
Join Date: Nov 2007
Location: Central Minnesota
From 38 years of wrenching on Jeeps, here is my recommendation for plugs for the XJ.
87-99: Champion Copper
00-01: NGK copper (Champion work okay, but the NGK gap holds up better over time because of the different ignition system).
No fancy Saturday morning commercial plugs needed for this very simple engine.......
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!