97 xj dies after running for an hr or so...

i have a 97 xj 4.0l automatic... she was sitting for a few weeks and when i started her up and she started i let it run for a few minutes took a drive then got home shut it off. when i came back out about a half hour later the xj was completely dead i tried to jump start it and would only crank so took out the battery had it tested they said it was fully charged. i put it back in and the xj started right up first turn of the key. the next day started up just fine drove it for a couple hours then stopped and again about 30minutes later tried to start and again completely dead. i took the alternator out thinking that was the problem but when the auto store tested it compared to the new ones on the shelf it passed 8 times in a row and never failed once... does anybody have any suggestions because im stuck my starter, alternator and battery are properly working but for some reason the xj likes to turn off randomly. it has also done this twice while driving and then i would stop and the xj would shut off when i stopped. please any suggestions would help me i need to get it running by this weekend. has anybody had any of these problems and know what is possibly going on? thankyou for your time.

Likely culprit is the Crank Position Sensor. CKP, but also called CPS. It reads the signal from the flexplate notches at the transmission bell housing. Failure after warm-up is a prime indicator. You could try cooling it off with cold water and see if it restarts. There are many threads to find on this if you search.

This link should assist you to troubleshoot whether or not your Crank Position Sensor or Cam Position Sensor has a problem.

http://www.naxja.org/forum/showthread.php?t=972057&highlight=Crank+Postion+Sensor

thankyou for the help I will check it out when I get back to my place and let you guys know what happens.

I agree with the others.

The #1 suspect for a thermal (heat related) failure resulting in a no-start on a 97 is the
crankshaft position sensor.

The #2 suspect (but happens far less) would be the ignition coil.

Good luck and let us know what you find.....the big money is on the crank sensor here.

Some sound advice you've gotten.

Crank sensor and coil are two items that often fail when hot--thermal failure.

As you haven't yet tested for spark when it won't start, it might also be the synch sensor in the distributor killing the fuel injectors.

Good luck.

surpisingly the ckp was fine but the problem that was wrong was a 3dollar fix had to buy a positive battery terminal then cut the positive cable back and clean the wires they were really corroded. lesson learned was remember to check the basics... could be the simplist thing that could go wrong... thankyou for the advice though.

Voltage drop testing to check your main cables:

http://www.aa1car.com/library/voltage_drop_testing.htm