[snapsstary]

I need some help guys. A buddy of mine has a 96 Cherokee with a 4.0 and an automatic transmission. Here’s the problem. Sometimes it will run like a champ other times it only runs for like 15 minutes and then dies and after it sits for a little bit it starts back up and may not do it again for a week or so. It’s kind of a crapshoot. He has replaced the fuel pump and the distributor from the cap to the crank gear. And it still does it. Does anyone have an idea of what it could be? and if some one has had this problem and it has already been posted my bad.

[tjwalker]

Originally Posted by snapsstary

Sometimes it will run like a champ other times it only runs for like 15 minutes and then dies and after it sits for a little bit it starts back up and may not do it again for a week or so. It’s kind of a crapshoot. He has replaced the fuel pump and the distributor from the cap to the crank gear. And it still does it. Does anyone have an idea of what it could be?

An intermittent failure like this could be a crankshaft position sensor circuit problem. They can be subject to thermal (heat) failure and can be kind of snaky to figure out if they don't fail catastrophically. Here's more on it. Pay attention to the part about connectors.

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Crankshaft Position Sensor: (CPS/CKP) Failure Symptoms / Testing

*Both the fuel gauge and or voltage gauge may not work/display

*It is possible that you may see a No Bus on the odometer (on newer models only)

*You will have no spark. Fuel pressure may check out okay at the fuel rail, but fuel won’t get to the fuel injectors

*For 96 + newer, sometimes the OBDII code reader has trouble connecting to /reading codes. Crankshaft position sensor failure may or may not result in a check engine light/fault code.

*Crankshaft position sensors can be intermittent resulting in an abrupt misfire. “Thermal failure” is common. Thermal fail means that the sensor fails when engine gets hot, but works again when engine cools down. Be aware of this when testing, as if you have a sensor that suffers from thermal failure, it’s possible that it may test GOOD as soon as it cools down.

*Don’t get tunnel vision and assume the sensor is bad (unless it checks out as bad with a meter) Damaged wiring or a dirty connector can inhibit the signal from making it to the computer. Check/clean/repair as necessary.

*Flushing the connector with electrical contact cleaner and a dab of dielectric grease when reconnecting is never a bad idea as sometimes the problem isn't with the sensor, it's resistance/debris inside the connector.
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CRANKSHAFT SENSOR TESTING PROCEDURE: 1991 – 2001 4.0L H.O. engines

1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.

2. Place an ohmmeter across terminals B and C. The terminals are identified as A-B-C looking into connector from left to right with the “notch” in the middle of the connector on your right. Ohmmeter should be set to 1K-to-10K scale for this test.

3. The meter reading should be open (infinite resistance). Replace sensor if LOW RESISTANCE

[1976j10]

My J10 used to do that. The problem ended up being the ignition coil. I'm not sure if that apllies to XJ's, but if nothing else fixes it, this is worth a shot.

[xjfever]

The coil and crankshaft position sensor are succeptable to thermal failure.

[snapsstary]

thanks guys ill pass it on and get back with yall

[david01]

When you replaced the fuel pump, did you check for loose connections in the wiring within the tank? On my 96 cherokee, the ground wire that plugs on to a terminal on the fuel pump mount, was a very sloppy fit. It would only ground part of the time. Sloshing of the gas would wiggle the wire back and forth and cause intermittent running of the pump. This cant be unique to my Jeep.. The other item that caused a similar problem for me was the pickup coil in the distributor. It would randomly fail for about 9 months before it finally threw out a trouble code. It was new 1 yr before when I replaced the distributor with a rebuilt (began failing in 3 mths). I never suspected such a new part to fail, but it did.
I replaced just about every other electronic part on the thing before I finally got the trouble code.. It was a pain in the wallet and the behind...