From what I've read, the timing chain stretches out as you rack up the miles on your Cherokee with a coil rail and at some point it gets outside of the range the computer can correct for it. Mine got there right after I installed a new crank position sensor and hit 130,000 miles.
The process is easy. You need a helper, a toothpick or small drill bit, some basic hand tools and a "mirror on a stick" so you can see the timing marks on the bottom of the cover.
Remove the coil rail, the first spark plug and the camshaft position sensor.
Carefully place a finger of the spark plug hole.
Have your helper bump the starter a little at a time until you feel pressure.
Break out your mirror and check your timing marks.
Use a ratchet or wrench, 19mm I think, to turn the crank forwards to the zero mark.
Remove the camshaft position sensor from the camshaft synchronizer.
Loosen the retaining fork that holds in the camshaft synchronizer.
Find the small hole in the outside of the housing for the oil pump drive shaft.
Find the small hole on the magnet inside that indicates camshaft position.
Carefully turn the housing on the camshaft synchronizer until you can align those two holes and insert a toothpick or drill bit straight through them.
Tighten down the retaining fork, reinstall the camshaft position sensor, spark plug and coil rail.
Enjoy quicker starts and having avoided the problems that this stupid sensor causes when it gets even further out of spec
The NAXJA guys
finally found my problem and provided me this link
to learn what the fix was. The process for finding top dead center and zeroing the timing came from my dad although I performed the work myself. It's basically the modern iteration of setting the timing on something you're led to believe you don't have to set the timing on.
Also, this is just the shade tree mechanic version of the fix. Alternately you can take it to a shop with a DRB scan tool and they can reprogram the computer to compensate the difference without ever having to open the hood or turn a wrench. A JF member in a thread I don't recall posted that the shop he went to wanted over $100 to do this. A guy in my Jeep club said he'd do it for free for me. Like anything else, YMMV.
(This may still be edited for terminology and additional accuracy.)
To illustrate the location