I have been working on my XJ for a while now, its a 2000 (4.0 Inline 6 Cyl) it had loads of issues, I bought it from a driveway where it had been sitting for 3 years. It had misfires and rough running all kinds of codes etc.... at first it ran really poorly, then i got it to where it would idle for 10 mins then cut out when it came up to temp, and would not re start. It was a mess.

I have finally got it to the point where it will start and run. When i run the car, and switch it off, it will re start after 5 or 10 mins, when its warm, but if i leave it over night it needs a PCM reset to start. Then it really labors on the cranking and i have to feather the throttle to get it to fire, but once it starts, it runs great and Idles ( a little high)

Parts list I have replaced:

Fuel Pump
1 injector
Coil pack replaced with a Dodge Caravan "Viper" Upgrade
New spark plugs
New Crank Sensor
New Cam sensor
Upstream O2
Downstream O2
Idle Airflow sensor ( on Intake )
MAP airflow sensor (under throttle body)
New Auto Shut off Relay
New Fuel Pump relay

All of these have been to rectify a problem ( or a combination of parts to fix a problem) After every part and sensor replacement I reset the PCM with the process of disconnecting the battery discharging the PCM capacitors, then the lights on lights off process. It will start smooth and clean. Then when it runs for a while and i shut it off, for a period of time (overnight) it wont start again and i have to reset the PCM to get it to start. In all the posts i have read the message is that the PCMS rarely fail so ..... I'm out of Ideas here. Happy to answer any questions, i'm a bit stumped. Thanks

 

What error codes are you having now?

What's the fuel pressure during all this?

Will it start if you prime (turn key to on 3 times then try to start)?

What's the spark during all this?

 

Thanks for jumping in to help Dave51.

I have no error codes showing on my hand held OBD scanner.
The last time I checked the fuel pressure it was around 50-53PSI I believe, That was after I installed the new Fuel Pump, which has less than 5 hours total run time on on. I haven’t rechecked it recently, I’ll get a look at it this weekend. When I press in the center of the shraeder test valve on the fuel rail, I get a solid squirt of fuel out so there is at least pressure there. I have a test kit I can get a reading.
It doesn’t seem to matter if I prime it or not, I can hear the pump engage, but if I turn the key once or multiple times to start it, that doesn’t seem to make a difference.

I went out again after I posted yesterday and cranked it and it labored crank a bunch of times and then fired into a really rough idle after about 15 seconds smoothed out to idle just under 1,000 rpm’s


******** Update, I just went out to it this morning, turned the key it cranked over and started, ran and idled at around 1,000 rpp with a little bit of rise and fall. Came up to temp, turned it off, turned the key and it started straight back up again. ********

 

Hey, I would start by checking all the ground wires, even add a new one from engine to body.

 

Turn off the parts cannon. Park the vehicle safely and start the engine. While it is idling, shake the wire harnesses that go to the engine controls/sensors. Harness to coil pack, crank position sensor, pickup coil, throttle position sensor, everything. Go through all of them periodically and see if engine rpm changes, and/or if those symptoms come up.

If all that checks out, then start checking sensors.