Relli8

Help please, i have a 96 cherokee with the 4.0. When im driving, out of nowhere the engine just shuts off and i have to wait around 30 minutes before it will start again. Any idea of what this could be?

Sizemic2

Check your CPS, thermal failure once warmed up can happen

Relli8

Thanks, ive been thinking the cps but didnt wanna take a chance and buy that when its something else. It does seem to do it more when its hot and it didnt start doing it until summer. Someone said the map sensor might be it. What r u thoughts on that?

Ghostwhite

Try and give a little more detail on your version of 'shuts off'.

Sputters and bucks?
Out like someone shut off a light switch?
Dash still powered?

Relli8

in the beginning if i went somewhere and shut the car off sometimes it wouldnt start back up again until it sat for about a half hour. but now ill just be driving along and the engine just completely dies just like a light switch. the dash still works. ill try to start it restart it and it will turn over but wont start. then a half hour later it will start. after the half hour, it takes one turn of the ignition and u can tell its gonna start then the second turn of the ignition it starts right up. A couple times it has bucked on me while driving but it doesnt buck right before it dies.it just dies. i have noticed that it seems the hotter it is outside the less time i can drive before it will die and not restart. but other than that theres no rhyme or reason.

jordan96xj

It does sound like a crankshaft position sensor that is failing more when it gets hot. Then working some after it cools down.

If you get a chance, pick up one of those small pen-sized inductive spark testers (they sell them at Advanced, Autozone, etc.). They are super handy to have in your kit, and you can check spark on a plug wire, or on the coil wire any time you please without removing anything.

Then the next time it won't start, or dies on you, when restarting use the tester to see if there is spark present on the coil or plug wires.

If there is no spark, than it sounds like a failing CPS even more.

If you find that you DO have spark, but it just cranks and cranks, then it will likely be a fuel delivery problem, such as a dying fuel pump, or the fuel injectors not being commanded to fire. (though a failing fuel pump probably wouldn't die so suddenly, but injectors not being commanded to open/close would die suddenly). So I'm going with the CPS being the most probable cause.

Relli8

i THINK I'M GONNA GO AND BUY A CRANKSHAFT POSITION SENSOR FOR IT SINCE THAT SEEMS TO BE THE ISSUE. IT JUST WOULD SUCK IF ITS NOT SINCE I DONT HAVE A LOT OF MONEY. BUT MAYBE I CAN TEST IT FIRST. BUT EVERYONE I TALK TO AND WHATEVER I READ UP ON SOUNDS LIKE ITS IT ESPECIALLY SINCE THE HEAT MAY HAVE SOMETHING TO DO WITH IT. IS IT EASY TI TAKE ONE OFF AND PUT ONE ON?

jordan96xj

If you test for spark when the vehicle is NOT starting properly, and you find that spark is present. It is NOT your CPS. My post didn't conclude that it was your CPS, it provided you with a quick and easy test to do in order to be more sure before spending your money. If you don't have much money, then diagnosing the actual problem before buying parts should be even more important to you. Imagine how frustrated you'll be if you swap that part, and nothing changes at all.

dirtyktm

Yup had this problem with my XJ . It would be driving just fine then quit like i turned the key off. It got progressively worse till I had to push it off the middle of I5 during rush hr traffic (good thing these things are light). 1 other time I coasted off the freeway. The Jeep would always start again in a few minutes
Replaced the Crank Position Sensor (with a Mopar part) $85. on EBay. Not a hard thing to do, I disconnected the front driveline to make it easier. Its been 4 weeks without a problem so I consider the problem fixed.
gotta love these Forums, thanks for the help everyone

beardenbulldog7

^^^This

Although Jordan read my mind, let me add on to it. Alot of the early 90's versions had issues with the wiring, more specifically ground cables and injector wiring. Give your computer grounds a good tug to make sure they're connected properly, and if you're really feeling froggy go ahead and replace the ends as they are more than likely dirty and fused to the bolt. If you are getting spark but no fuel, then clearly your CPS and ECM are working as spark would not occur without either one, plain and simple. First off, check to make sure you have fuel pressure, and when you have determined that the fuel pump is not the issue then the next time you get it running, squeeze the wiring harness starting at the computer and moving up to the injector rails, or until you find where squeezing it cuts the engine off. In my 1993, the main culprit was a green and orange wire that junctioned going in to the injector harness casing. If you find that this is the problem, here's how you fix it:

To fix the injector harness, the casing should come apart in two by disconnecting the tabs located on the bottom. Inside you will want to look for a green and orange wire that is junctioned inside of a black rubber-like casing with 6 more wires of its type coming out. To fix it you will need:

Soldering iron w/ solder
Heat shrink wrap
Lighter
Wire strippers
Electrical tape
Knife

To start, simply take your knife and cut the black rubber-like casing from around the wires and discard. Next, you'll want to pull the wires apart and strip them to remove the glue-like substance that previously attached them. The next part depends on how good of a soldering iron you have. Start by cutting a section of your heat shrink wrap and slipping it over the wires, moving it down some to avoid the heat from the iron. I started by taking 2 wires and soldering them together, then adding one at a time until I eventually had them all soldered together, then slid the heat shrink wrap up and used my lighter to seal the connection. Afterwards, wrap the group of wires up in electrical tape and pack them back in to the casing.

If that's not the issue and you've ruled out every possible sensor and computer being the problem, keep squeezing at the wiring harness until you find the short.

Good luck!