Heres one for ya. I have an 87 with a new 4.0 and it starts when it wants to. It cranks good, plenty of fuel, and good spark. Tested the cps and its good. I have spark at all six plugs. Heres the kicker even with spark and starting fluid it wont start. I couple others and I think it may be the ecm? Just seeing if you guys have any ideas?

 

Could it be a worn out ignition switch? Maybe its only working when it wants to. Try jumping the starter next time to see if it fires up. Just a thought

 

check the TPS, and IAC. they might be sticking, or your throttle body might be super dirty/carbon deposited. check those and see. I had the same issue for a bit. if none of those things fix it, check to see if your coolant temp sensor is bad-if it reads a low temp, it will overfuel itself to get up to operating temperature and too much fuel will cause starting issues.

 

Dose it run good when it starts? If it dosent and won't run on starting fluid I would check the timing.

 

Not really Jeep advice but if there is spark, fuel, and compression, about the only thing left is it's flooded.