Hello.
We have a strange problem with a non-HO XJ 4.0.
When the engine is cold it starts and runs without a problem. After becoming warm it backfires and turns off. We can start the engine again only after it cooled down.
What could cause the problem?
Perhaps a broken sensor?
Thanks for your help.
nicolas-eric


Cold:

Warm:

 

check the coolant temp sensor. What are the specs (year, engine, trans, any mods to the engine) of your jeep?
My 2000 cherikee has the temp sensor on the thermostat houseing.

 

Thanks!
Where is this sensor located?

 

some have it on the thermostat houseing (front of engine above the water pump) others have it on the head towards the back of the engine (unsure).

 

Have you checked for fuel pressure when it does the "warm no run?"

 

Yes. We installed a new fuel pump and it was still the same.

 

How about coil?

 

We didn't check the coil.
It works with a cold engine.
Or could there be a problem with the coil only with a warm engine?

 

Mine started doing the same thing right after I bought it....changed the ignition control module, coil, crank position sensor, and the fuel pressure regulator and haven't had the problem since!! Don't know which part was bad but they were all factory parts at the time...don't know if it helps but that's what I did!!

 

Sorry that was wrong.
My buddy installed a new coil the last time he was wheeling. But nothing changed.

 

I would change the crank sensor and the pick up coil (AKA the cam sensor), both of those sensors will cause the problem you described.

 

checking for codes even if no ight is on could narrow this down

 

Sometimes coils fail once warmed up, but if its already been changed disreguard.

 

I would definately check the crank sensor, I was talking to a guy on friday that had an 89 cherokee and he said that he had a problem with his it would warm up and die, then it wouldnt start again and he would spray it with water then it would run fine for 20 minutes or so and die again. Maybe hose it off and see what happens lmao

 

Thanx!

With a new CPS it runs better but the problem is still there. After becoming warm it runs rough and sometimes it dies. But now it can be started again after that.
I'll post a video in some hours.

What else could be the problem?
What's the cam sensor? Pic?
I'm German and don't know the right German word for that.