Intermittent engine shut off.

It's my son's 97 XJ, 150k, AW-4, 4.0. We've had it a few months and it has run well. We have replaced the plugs, cap and rotor, and coil. The plugs were black, but otherwise fine. It doesn't blow oil(YAY!).

The other day he told me that it died as he was turning into the driveway. I went to drive it a few days later, and it died shortly after starting. We replaced the CPS this last Saturday, and it seemed to be running well. Then the dreaded engine dying happened as before.

I have three thoughts: one is that the new CPS is bad, or out of spec, two is that readjusting on the bell housing might help, three is that something else is wrong.

Any other thoughts??

Fred

Test the CPS/CKP crank sensor, Tim_Mn has posted the information with diagrams numerous times.

What happens AFTER it dies? Restarts fine, cranks but no start, won't crank?

As the problem represents after the part change I doubt it was the that part in the first place.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Do the same for the grounding wires from the starter to engine block, and from the battery and engine to the Jeep's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU may behave oddly until you remedy this.

With a Jeep you don't know the service history of, you should just go through all the basics and inspect, clean, or replace parts as seems logical for the age and mileage.

Do a visual inspection of the engine bay wire harness and check all the wire plugs making sure they are firmly connected. You may want to get a can of electrical contact cleaner and disconnect and clean as many as possible.

Where did you get the CPS ? The CPS and the TPS are important enough sensors that I prefer to get them from the dealership or at the minimum NAPA. Cheap parts are cheap for a reason. The CPS does not need adjusting if it has two mounting bolts.

Replaced the plug wires yet ?

Clean the Idle Air Controller. Add a bottle of injector cleaner to the next two gas tank fill-ups.

Consider testing or replacing the Camshaft Position Sensor in the distributor.

i know that the 97 had trouble with the harness and the shut down reminds me of an ecu problem we had on a grand but i would start with the small stuff and work your way up... i hate electrical gremlins good luck.

Along with the above good suggestions, I'd get a meter and check primary/secondary resistances on your ignition coil. Takes only a few minutes. Replace coil if your numbers are out of spec.

I've been on this forum since before Naxja. I have read more than one instance of new CPS's failing, as you note, paricularly after market.
There is more than enough play in the mounting of the CPS to effect function. This has also been reported.
Why would one plug wire cause an intermittent no start, which by the way implies that it dies and does not start the next time?

I agree with the suggestions to go over all connections very carefully. Could be a loose connection somewhere but could be more in depth also. I had a random stall/no start on my '92 4.0 that drove me absolutely batty. Mine would just randomly quit for no apparent reason. I carry a spare CPS and tried that first. No luck. I checked fuel pressure and found it to be fine. But, with engine off checking fuel pressure, it was good but, had very little volume. Bypassed the resistor to no avail. Replaced fuel pump and still didn't fix it. So, while it was running, I carefully started moving the harness around looking for some sort of loose connector. When I would squeeze the harness at the firewall where it tee's to the engine, it would kill it. Unwrapped the harness and started puliing and jiggling each wire. Didn't faze it. Squeeze the whole bundle and it died. I found that the engine has a fuel pump shut down wired into the injector circuit. The injectors have 2 wires. A power wire and the shutdown wire. The shutdown wires are all crimped/soldered together and I had 1 loose one in the bunch. Cut and re-soldered it and haven't had a bit of trouble since. Been good for a year now. Anyway, good luck in your hunt.