I have a 1991 Cherokee. 4.0l, Automatic. Every once in while it will not start. The problem has gotten worse. If I wait till the next morning it will start. Checked fuel supply = GOOD. Checked spark from coil pack = NONE. No spark at all. Disconnected battery retried, Moved the shifter thinking it was a neutral safety switch issue, Played with key thinking a key switch problem, nothing. The only time it started earlier than next day is when I difted down a hill in nuetral put it in park and tried to restart and it did. I am mechanically inclined but this one is stumping me!!!! Have off road event to go to and worried it will stop there. PLEASE ANY HELP!!!!

 

The #1 cause of "thermal" (heat related) failure on the Jeep 4.0 is the crankshaft position sensor. Without the input signal from the crank sensor to the computer, you will not have spark and you will not have fuel going TO the fuel injector.

The #2 cause of thermal failure is the ignition coil.

Time to start doing some testing (only when symptomatic) to see if either of the above components are out of spec.

Good luck!

 

The darn thing will not start sometimes wether it is cold or hot. Sometimes it has been sitting for a cpl days and willnot start, other times it has been running fine.

 

I would guess the CPS as well....

 

diddo!

 

starter turning over at all?

 

engine turns over fine. it has been 4 days has not done it. It might be next time or a week between issues. The pump is kicking on and building pressure. engine turns over. NO SPARK from coil. It can happen when it is warm or dead cold. I think i am going to replace coil and possibly crank positioning sensor anyway see what happens. replace both for $100.

 

Crank sensor fails more commonly than the coil, but both are suspect.

Personally, I'd test but if you are going to replace, start with the crank sensor.

 

I had the same problem in my 96 xj its more then likely ur crank sensor... I did that in mine and never had that problem again