IIRC you have a 90 which has the only year of the TBI injection. Mine was a 91 which has the later style injection which was kept for the later production jeeps. When I replaced the failing dist in my 91 I screwed up and had it one tooth off. It ran, started and drove until I went to get gas and it would not restart. Yes, you can set the initial timing and the comp will adjust itself to a point. I say that meaning it can only compensate so far. This seems to be the same for many of the vehicles Ive owned (vehicle junkie 200+ and counting) Typically having the ignition timing off causes hard cranking, rough running, possible back firing up thru the carb or T Body, may smell funny running due to its poor running. low power and that type of issue. The timing should not slip out of wack unless you have a failure of some sort. Dist gear pin broke and the gear spun or the can teeth went away, it came loose and spun a bit perhaps the timing chain slipped a tooth or two which would screw up cam and ignition timing. Just so hard to guess on a comp controlled vehicle without more diagnostic testing. The computers do go bad in these things, its not uncommon by any means. Possibly talk with the folks at
www.wranglerfix.com aask if they have any insight into whats going on at this point on your YJ.