Thanks for all the posts and replies here! They helped me get to the bottom (I think) of my latest issue on our 1998 XJ 4.0L.
I recently replace the ignition lock cylinder and it has been starting great for the past week. Previous symptoms were intermittent starting over the past 6 months, getting more often recently. It would start and run great for a week, then 2-4 days, then the battery would die and it would need jumped. Start in the morning and then not start in the afternoon. I was always able to get it started with a jump. Sometimes it would crank, crank, crank and not turn over. Give it some gas on crank, still not turn over. Turn the key to prime the fuel pump a few times. Always was able to get it started though and seemed random on how would get it to start. Battery is about one year old. I had charged it several times and had it tested to know it was still good. I had cleaned the grounds, replaced the battery cabling (relatively inexpensive and made sure I had good connections), replaced the starter (had it benched tested and it showed some pausing/hesitation in the solenoid), tested the fuel pressure. Fuel pressure tested at 48-50 psi running, then turn off, and pressure drops to 25 psi after 5 minutes (so I think I have a future fuel pump issue coming at me). Did parasitic draw tests too. Sometimes get a small draw (less than 1 amp), sometimes no draw.
After realizing I could take the key out of the ignition at any position, even with vehicle running, I replaced the ignition lock cylinder. This made sure the ignition was in the off position. I think it was sometimes not completely in off position. Now nothing is drawing battery overnight to drain battery and gives engine enough power to start on its own. The intermittent start makes some sense now knowing we probably sometimes turned the key to the off position randomly, then sometimes not quite in the off position, so battery would drain slowly.
