96 XJ 4.0 Died while on the trail.

A friend of mine just bought the Jeep stated and drove it over 3 hours from where he purchased it all the way home on the highway at 75 and it ran great. We took it out and started cutting the first trail through a foot of snow 10 feet at a time nice and slow not beating it and got about 8 miles out into the Montana Rockies and it just shut off. Long story short we got it towed out and started testing things today. No spark but we have fuel. There is no power going into the plug at the coil. I am trying to find out what supplies that plug with power. There are no blown fuses, and it seems all the ground wires are fine. According to the wiring diagram in the Chilton the wires run to the computer and to the Auto Shutdown relay. I tested the relay and swapped it out with another one with no change. It will crank and crank but no power even getting to the coil. Any help would be greatly appreciated. It seems some people have had similar problems after searching but no one had the exact same symptoms. Thanks in advance for any help.:huh:

Crank Position Sensor or Coil pickup. If you have a multi meter you can test them both to see which one it is, or both. The Chilton's will tell you how to test each. I think, but I'm not 100% certain that the center will be ground and the outer two wires will alternate 5v as it cranks.

Where is the coil pickup located? Im more of a GM mechanic and have never worked on a 4.0.

I think if its is the crank position sensor it wont even crank. I had a similar problem and I just replaced all of the ignition stuff, distributor, plugs, coil, and it seemed to work.

Pull off the distributor cap and it's the disc situated below the rotor with the three wires coming out of it. Also, when you said you have fuel...how do you know? Did you check the schrader valve for pressure, or did you check to see if the injectors are firing? Just because the pump is priming the rail doesn't mean the injectors are firing. It will crank with either of those sensors not working, but it won't start.

Yes we did just check the schrader valve for fuel and it spit out fuel with plenty of pressure but we definitely have no spark or power to the coil via the plug coming into it. i will be pulling a plug off of an injector tomorrow and testing it with a multimeter, along with testing the crank sensor and the coil pickup. thanks

Check the crank position sensor, driver's side top of the bellhousing. Sounds like the unique symptoms of a bad crank sensor.

Did you check the battery? I blew one up playing in the rocks once.

hammondrckr said:

I think if its is the crank position sensor it wont even crank. I had a similar problem and I just replaced all of the ignition stuff, distributor, plugs, coil, and it seemed to work.

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it will still crank if the cps is bad.

a bad NSS will keep it from cranking though

Find out what it was?

Well i tested the crank sensor with a multimeter and as long as i had the meter set correctly it read over 100 ohms which is well out of the limits for a good sensor. We are going to install a new CPS tomorrow and I will give you all the update to let you know if that was the problem. Thank you all for your responses.

If you continue to have problems after the new CPS, and all other repairs fail to fix it, check the CPS's plug closely. Mine had similar problems, and it turned out that the plug on the vehicle side of the wiring harness was bad. Luckily, mine would still start occasionally, so I hadn't bought a new CPS just yet. I cut the plug out of the harness, and butt-connected the wires together, and it's worked ever since.

Also, another thing to check would be the transmission-to-block clearance. After fixing the CPS, and wheeling mine for a while, I noticed it liked to shut off when the body got good and twisted. It seemed to get progressively worse and worse. One day out on the trail I couldn't go 2 feet at a time down a good twisty section without it shutting off. I checked the bellhousing bolts and sure enough, the driver's lower bolt had backed out, and the P.O. didn't put the upper bellhousing bolts back in after they had the engine out for an overhaul I tightened the lower bolt, and the problem went away.

Well guys.....We replaced the C.P.S. this afternoon and the 4.0 cranked right up to life.....thank you very much for all of your responses...you made fixing this problem a lot easier..

Anyone who's owned a 4.0 for any amount of time has been there. Glad you got it fixed.