Engine shuts off....going nuts

OK its a 95 XJ,180,000 miles. Engine shuts off but then is very easily started back up, did a fuel filter and plugs but still same problem. It seems to happen at idle more than at highway speeds, but it did "buck" at highway speeds a couple of times. TPS and IAC are fairly new. Now it doesn't sputter as if its fuel, it just shuts off as if someone shut the coil off and all the electrics stay on, i.e. radio and such, it doesn't throw an engine light. I did replace the fuel pump and auto shut down relays but no luck.
Any ideas??
TIA STROKER

Don't know if the 91+ cherokees have this, but my 89 has a little ceramic resistor block on the drivers side fender just in front of the EGR vacume valve, It reduces the voltage to the fuel pump when running, it can crack and cause eratic shut downs like yours is doing, its cheap to replace. HTH

Josh

STROKER said:

OK its a 95 XJ,180,000 miles. Engine shuts off but then is very easily started back up, did a fuel filter and plugs but still same problem. It seems to happen at idle more than at highway speeds, but it did "buck" at highway speeds a couple of times. TPS and IAC are fairly new. Now it doesn't sputter as if its fuel, it just shuts off as if someone shut the coil off and all the electrics stay on, i.e. radio and such, it doesn't throw an engine light. I did replace the fuel pump and auto shut down relays but no luck.
Any ideas??
TIA STROKER

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Damned if that doesn't sound like a CPS issue. How recently was that replaced?

ACE said:

Damned if that doesn't sound like a CPS issue. How recently was that replaced?

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Yea, check to see if there is corrosion in the CPS connector. FYI, make sure it's not close to the exhaust manifold. Mine melted and left me stranded.

I third the vote for CPS ... also my CPS looked good, and no corrosion on the connector and it still did it. It actually was doing it since it was about 2yrs old, and the dealer even couldn't catch it, as it didn't throw any codes into the comp......

CPS is only about a year old.

Spent an extra day on the road coming back from Moab becasue Chewy's rig was doing the same thing. Fixed with a coil wire manipulation and new CPS.

Evan at a year old I think your CPS just took a dump.

Bones :skull1:

yup.... a year old CPS doesn't mean much... mine started acting up at about 2yrs old? so what's a difference of a year? I actually also came across a commentary on MSN auto's today talking about an increased rate in CPS in late 90's XJ's

I had the exact same symptoms on my '93. Turned out the CPS wires had gotten a little too cozy with the exhaust header and melted the insulation off an area about two inches long. From time to time this bare area would make ground contact with the header and voila - instant dead engine. A couple of times the contact must have been so slight or quick that the engine didn't completely die, but fell flat on its face for a split second and then recovered. That had me guessing for a few days before I spotted the bare area.

This could happen to a CPS of any age, so make sure to keep it tied back away from anything hot or sharp.

What Rd (f.k.a. ArmStrong) said:

I had the exact same symptoms on my '93. Turned out the CPS wires had gotten a little too cozy with the exhaust header and melted the insulation off an area about two inches long. From time to time this bare area would make ground contact with the header and voila - instant dead engine. A couple of times the contact must have been so slight or quick that the engine didn't completely die, but fell flat on its face for a split second and then recovered. That had me guessing for a few days before I spotted the bare area.

This could happen to a CPS of any age, so make sure to keep it tied back away from anything hot or sharp.

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Just curious, but what's the cps?

tireroastin93XJ said:

Just curious, but what's the cps?

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Crankshaft Position Sensor
It is the sensor that allows the engine to control its timing by signaling the computer on position of the crank.

Bones :skull1:

Thanks guys I'll try a new CPS, gonna be hard to tell because it does it after long trips, when im just running around the area its fine(short trips). But i'll replace it anyway to see.

Often it is the wire harness connector instead of the sensor that is the problem. I went thru this with my cps on my 89. Replaced it and it was good for awhile. Then the unplug and replug of the connector fixed things for a couple of weeks. Then it dawned on me that the engine harness connector that the new sensor plugs into never gets replaced in the process of installing a new sensor. Mine looked a little worn. The internal metal connectors stretch and loose tension. Here is a post I have posted a couple of times in the past:

On a pre 91, if on a crank but no start the unplug and replug of the cps wire harness connector gets you going you may just have a wire harness connector going bad and may not need to replace the cps sensor. Here is how to test: hook volt meter to both wires from cps sensor w. harness unplugged. Set the range on meter to less than one volt. Crank engine and if cps generates .5 to .8 or more volts it is ok and your connectors need tightening or replacing. I got my parts for a couple of $ at pepboy but advanceauto.com also has them. They were made by Dorman under the Motormite Conductite tech grad name # 85303, 85304 and 85305. There are about 5 pieces in each box. You can also get a small tool set that helps on the install number 85360. I fixed my 89 this way a couple of months ago when I got tired of unplugging and replugging the connector every few weeks. My cps was only 1 yr old so the engine side harness connector part was worn out. I replaced both the female and male side internals of the connectors and it not only starts every time but the idle was also improved. Greg

Note on post 90s the cps is a three wire I believe and is provided w. a 5 volt signal from the computer instead of self generating up to a 1 volt signal like the pre 91s.

Bones said:

Crankshaft Position Sensor
It is the sensor that allows the engine to control its timing by signaling the computer on position of the crank.

Bones :skull1:

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Yep, I had to replace mine on my 93. It would die and restart. Finally it died and wouldn't restart, had it towed to the shop and it started but then died again.
Mike