1998 wrangler 4 cyl 110,000 miles. The engine

There has to be either smoke or a leak. Have your Mechanic do a compression test on all cylinders. It will give you a lot of information on your engine

ever get a full 60k mile full tuneup this decade, no ? really?
the first tests are,.
is the ASD relay dropping out?
and is there DTC errors scanning the thing with any obd2 scanner made.
1:key in
2: scanner in. and on, it talks ok.
3:crank for 5 seconds
4: release key, not off, is scan tool puking DTC errors, BINGO !@!!

the 8 ways for ASD to drop

http://www.fixkick.com/Jeeps/ASD.html

if the ASD does not drop cranking...>>>????
check spark now. at all cylinders, no engine stated.
check fuel pressure
check engine compression.
all that good, crank with test fuel
if engine flooding crank with wide open throttle to clear the flood.

is this the 4.0L???

replace the fuel pump,the check valve that holds pressure on the fuel is in the fuel pump.The fuel in the lines is draining back into the tank

Check the crank position sensor. If this goes out, when it gets hot, the sensor will think the crank/timing is in the wrong position. They did this to prevent engine damage in the event that your timing is off. However, when the sensor gets old, as it gets hot, it malfunctions shutting off the engine. Then, when it cools down a bit, all is well.
IF IT IS THE CRANK SENSOR, REPLACE IT IMMEDIATELY. Repeatedly trying to start an engine w/the CPS out can throw the timing off. This happened to a friend's Kia Sepphia once and it locked up her engine.

The starter is most likely the problem,tap on the starter lightly with a hammer while trying to start the engine,dont get run over doing this it will take two people,if the engine starts,the starter needs replacing.

if you jump a car then take it to get tested it will pass no matter what it off and get it tested maybe???

It sounds like your new crank sensor is defective. It should be under warranty.

clog in your fuel line or you need to change your fuel filter.

What engine?

   What engine is in the Jeep. 4 or 6 cyl?  how many miles or her? May be a timing chain concern but i will need the asked for info.