OK, 99 Grand Cherokee is new to me 4.7L. I've done a little maintenance such as changed oil, tranny fluid, and put new sneakers on it. I have put ~2k miles on the vehicle since purchase and yesterday I had a check engine light with code P0108. I had been planning to change plugs and air filter so I decided to do this minor maintenance, reset the light and see if it came back on. I pulled out the filter box connecting hose and air delivery system (don't know what the plastic parts are called) and changed plugs. Had two coil boots that were cracked / broken where they attache to the post / retainer so I replaced them.put it all back together, put my code reader on the vehicle and cleared the code.
Went to start and it will not turn over. Lights come on, I hear the fuel pump engage and it will not even click. This thing has not had issues with starting or battery power. Decided I'd throw the battery pack on it, which is at 92%, just in case and no change. But my charger / Jumpstarter with 200 amp jump start on it and nothing. I tried disconnecting the negative lead from the battery to let it reset but no change. Any idea what I might have accidentally hit to cause this.

Thanks in advance for any advice

 

OK, may now understand my issue but will have to look up next step. May have cleared more with the code reader than I wanted. I put the code reader back on and have the following message:

"No Powertrain DTC's or Freeze Frame Data is presently stored in the vehicles computer"

 

Well, took it all apart again and reviewed everything, all looked good. 12.4 volts on the battery, all fuses looked good, swapped starting relay with wiper relay and no start. Reassembled all the intake pieces and one last try... it started. Drove 20 miles and parked in a convenient location, shut it down and it restarted. Not a lot of confidence with no clue as to why so I'll just run it close for now.,..

 

I had the same problem. 99 WJ would not start, everything you just described is what I also had. I found it was the shifter cable that comes from the shifter itself and the clip that holds it to the shifter base. It was loose and not clipped in correctly. I fixed it and clipped it in correctly and tested it, and to date no more problems. Starts every time. Maybe this is your problem maybe not. Just FYI.

 

Thanks, I'll double check it!!!