Friar Mountain XJ

98 XJ/4.0
My XJ runs great until it's driven 10+miles. It either stalls and shuts off or if I turn it off, it won't restart until it's cooled. It wasn't sending power from the coil so I replaced it along with the distributor cap, rotor and coil wire.
Any help will be greatly appreciated!
Thanks,
Mark

Garrett S.

Does it have spark when it dies?

dzywicki

That is pretty classic crank position sensor (CPS) failure mode. Works fine when cold and then dies when hot. Repeat cycle. There are some test procedures if you do some searching. If you do repalce it, I'd use either OEM Mopar or Echlin. Some of them are very cheap for a reason.

tech

Crank sensor 2x

Friar Mountain XJ

Garrett S
It doesn't have spark after it dies.
dzywicki
tech
Thanks on the crank sensor recommendation. Being that it's never been replaced, I will and with OEM Mopar.

dave1123

A little tutorial on crank sensors. It's a magnetic switch that senses changes in it's magnetic field by metal passing close by, in this instance the windows in the flexplate/flywheel. Mopar sensors are made using neodymium magnets whereas aftermarket ones generally aren't. The one I put in my WJ 4.0L would stick to a screwdriver. This is why they cost more.

Friar Mountain XJ

I ordered the Mopar sensor this morning and it should be here in a few days. Thanks for the info!

4.3L XJ

Since you don't have spark when it dies, I would suggest looking at that cam position sensor in the distributor. The crank sensor affects injector timing

Friar Mountain XJ

Will do. I'll order one tomorrow. That would be much easier to get to! I'll replace that first and if it fixes the problem, I'll keep the crank sensor and hope I never have to replace it!

Friar Mountain XJ

4.3 XJ
Based on your handle, do you have a vortec V-6 in an XJ?

4.3L XJ

Yes I do. Had it for about ten years now and wore it out. Looking to replace it with a V8 and update a little

Friar Mountain XJ

I had thought about a V8 swap but I was told it would never pass inspection and it would have to be off-road only. I wasn't ready to make that jump.

4.3L XJ

I had to jump through some hoops for sure to make it smog legal, and it ended up costing more than I planned. But it all worked out in the end

Friar Mountain XJ

I saw pictures of your rig earlier in Cherokee of the month, at least I think that was the thread, nice ride! Would love to see under the hood.

dave1123

I would suggest nothing works without a CPS signal. The PCM won't turn on the ASD relay without a signal from the crank sensor. The ASD relay controls both the ignition and the injector circuits. It won't turn on the fuel pump as well without that signal except for that initial fuel rail charge when you first turn on the key. It's true the cam sensor tells the PCM which injector to activate, but the crank sensor tells it WHEN to activate the injectors and fire the plugs.