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This has been covered many times on the jeepforum.
Your problem is probably electrical, and very possibly the ignition module under the wiper water bottle on the left front fender.
Look at your tachometer when your turning the engine over. Does the tach needle bounce up and down a little? If it doesn't, the module is giving you headaches. You may want to try to find one in a junkyard somewhere that you can plug in and try.
Also, if it's the module, you can sometimes push the vacumn advance lever back and forth a few times, and if you hear a faint clicking noise, you may be able to get the module to fire again.
Hope that helps. This advice comes from personal experience. Same thing happened to me
DOMINICAN STORM RIDERS JEEP CLUB, SD,RD, Member #1, 1990 Cherokee, 4.2, Autmatic, A/C, Stock.
It's my seventh jeep, had em' all my life, did all my 4 wheelin' on sand dunes.
My jeep loves me.. right?