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TJ 1999 randomly cuts off while driving for a second


NAXJA Forum User
Hello everyone,
I'm new in this forum and I would ask some advice regarding this TJ with a very random problem.
The vehicle runs fine all the time but, at one point, engine cuts off for one or two seconds while driving and then back normal, sometimes is not possible to reproduce the problem for one or two days, it doesn't memorize any DTCs the rpm gauge doesn't drop. The cut off is very sharp, like someone switch off the engine and start again very rapidly.
CPS, distributor sensor, spark plugs, distributor cap, high voltage cords and coil were replaced in the summer during a big service.
After that, we replaced the coil gain with a known good one, TPS, relays, and re-wire positive and grounds on the PCM plus re-wired the connection with the coil.
One time I managed to reproduce the problem while my oscilloscope was connected to the injectors and the signal was there.
I'm suspecting that the distributor could be the problem, since the shaft has some play left and right or maybe the PCM itself, I read many stories about PCM.
Does someone had the same problem?

Thank you

A couple questions to try and better define the problem:

Is there any driving behavior that correlates to this issue (does it happen when you first apply brakes, make left turns, make right turns, hitting significant bump, etc.)? does it happen if you're simply sitting in the driveway idling it, or does the vehicle have to be moving for it to happen?

Is it only the engine that cuts out when this happens, or do all switched 12V items (climate blower fan, radio, etc.) blink out too?

It sounds to me like either one of the new sensors is acting up or you have a loose/damaged connection somewhere that's randomly intermittent.

Is the new CPS a genuine Mopar one? Been reports of aftermarket sensors not working as well as OEM.
Good morning and thank you for your reply.
It happens during normal driving and cruising with a 25/30% of throttle and around 2000 rpm, was never noticed on hard acceleration. Is not related to turning or speed bump, I also tried to drive on a corrugated track, I said, if is a connection or a wiring problem that would be the place to reproduce it but nothing, it seems it not happens on off road... Apparently, with new information, the problem starts after replacing the A/C compressor clutch and condenser from another garage, it seems that with A/C on the problem is more frequent, I will try again this today to confirm.

I don't think the CPS sensor is original Mopar. I don't have experience with Jeep but only with european vehicle but, usually when the CPS goes bad, the rpm gauge also goes to 0 or at least shake a lot, in this case the rpm gauge remain in his position, no drops or shake, maybe someone here with more experience than me on jeep can confirm if is the same with this type of vehicles.
Nothing cuts off except the engine, no radio, no light no gauges on the dash, the engine got off, time to count "1" and it runs again.

Thanks again for your help, I have no experience with Jeep, your help is very precious.

Hm. Since the problem seems to have started since the A/C work and having the A/C on makes it worse, a good place to look next is that area as it suggests that something got disturbed during that work.

At the very least, it's probably worth taking a good close look at any wiring harnesses/connectors near/around the A/C compressor and condenser - pinched wires or damaged/loose connectors could have resulted from the job, and could be disrupting voltage or ground to other parts of the engine bay. If you see any damaged wires or connectors, that's at least part of the problem.

Another thing to try: with the engine idling, take a voltmeter reading across the battery with the A/C both on and off - if there's something wrong with the new compressor clutch, it might be causing a "brown-out" - reduced voltage to the point where things like the computer can't run (usually that sort of thing requires a minimum voltage to operate, and if the power drops below that it's like it was "unplugged"). I'd expect a small dip right when the clutch activates and it should recover quickly to the normal approximate 13.5V for engine running; if it dips significantly and does not recover fast, it may be a sign of something not being right with the clutch or its wiring.

The sentence about the A/C work being "from another garage" is a little unclear - that work was done by a professional mechanic? If so, how recently?