MHG

So for some reason I needed to create a new account here. Haven't needed to post in a while and I guess they dumped my account.

4.0l 2000 Sport Could not start. No spark. Occasional code for crank sensor (i forget the code number). Replaced Crank Sensor with MOPAR, starts right up. Ran a little rough. Down the road no issues then stalls. On the way home, needed to drive with two feet every so often to keep it from stalling at a light. Even stalls on highway at 55mph with throttle. No codes, just dies. It particularly likes to die in reverse.

Mechanic we use at work says, possible Cam sensor as well. Both lead to timing issues. Replaced that with no change.

Drove it to local mechanic. He said I need to bring it to someone else because he would just be guessing. "To confirm its timing you need to scope it" and apparently not all mechanics are created equal.

There is no doubt the crank sensor was bad so I looked up all the wiring and ohmed it out to the PCM. Signal line is zero ohms. Ground and Power both run through factory splices and those are about .3-.4 ohms each. I am guessing the inductance of the other sensors is the cause of that slight increase in ohms. The signal wire is the only direct wire.

PCM Is my next guess because I cant see much else causing a stall at 55 mph...

For reference the jeep has 140k miles. Long block was replaced with a Jasper at 130k miles.

MHG

So hooked it up to an Autel Maxsys to see what I can see and test.

fuel pump tests fine
ASD. Test fine
injector shut off one at a time test fine
reset the PCM successful and it still runs like crap.

monitoring misfires and they are mistake zero but intermittently they all flash 255.

I personally don’t thing these old PCM’s don’t respond fast enough or have limited diagnostic capabilities. But it’s my only XJ and I have seen others online monitor misfires quite well. Which bring me to my next point. The scanner was taking for ever to connect and in many common tools it could not connect.

I am leaning towards the PCM. I can’t see the coil pack making it quit running outright and not throw a code.

MHG

Well its not the PCM. Guess I own a spare PCM...

MHG

These old schools PCM's are worthless on a diagnostic meter. Every reading is all over the place leading you down the wrong path. Although I was able to test the IAC stepper and monitor (somewhat) the live data. Unplugging injectors made no difference, so I am guessing the missing is on all cylinders. But misfire monitor shows nothing. So I decided to replace the coil pack and that fixed the issue.

MHG

Und of day Bad Crank Sensor and Bad Coil. For what its worth the aftermarket cam sensor works just as good. My sync was off about 13 degrees but no difference in running after correcting that.