Fuel Vapor Issue----NO FUN

I have a 2001 XJ 4.0L Auto on 35" KM2's and 4.56 gears. It is my DD and I've never had an issue running around town. However the Jeep has stalled on my 5 times now but only when working really hard.

Three times it was hot out and I was in stop and go traffic. The other two times were climbing the 330 up to Big Bear for off-road trips. The problem seems to be air in the fuel system or the fuel turning to vapor. I can bleed it out of the system and after 10-20 minutes be on my way.

My newest theory is the transmission is getting so hot its turning the fuel in my fuel lines to vapor. Is this possible? Can anyone think of any other reason I would get air in my fuel system when the Jeep is working really hard?

I replaced my fuel pump last week since it was old and to rule it out as the cause. I have no other leaks in the system either. It's quite annoying since it usually happens when I'm headed to wheel!

Thanks up front for any and all help.

Sounds like a vapor lock issue or you have an exhaust leak blowing on the fuel lines.

Huge advantage to the older "pressure return" fuel system - it could bleed itself!

You can try fabbing up a heat shield for your fuel lines, using light-gage aluminum should work (depends on the area you need to cover - for smaller areas, I used to use soda cans. Worked great!)

It is not likely vapor lock or boiling fuel - the system is under 50psi, you 'd have a hard time boiling it if you tried.

The problem is most likely the Crank Position Sensor which is located on top of the tranny. This is a well-known issue with the XJ and the most common cause of no-starts or Jeeps dying when hot. When they get hot, they fail and the Jeep shuts down until it cools down. Deal with it by letting the Jeep cool down, or get a new CPS. Do a search, this issue is very common. I fought identical symptoms for months before I figured it out. I would always die at the same point on the same hill.

Next time it dies, test the CPS (look at other threads for how to do this) and check it out.

So if it's the CPS do I just replace it, or is it still a heat issue and I need a Trans cooler? I'm hoping mine is just old and hated the heat cycles and needs to be replaced. I'll search this site as well when I'm not on my phone.

If it is the CPS:
1) Make sure you don't have an exhaust leak in your manifold - that makes the problem even worse by spitting hot exhaust directly on the sensor and it will just kill the next one too.
2) A tranny cooler is a great idea and will help.
3) Replacing the CPS should also help. When they get old, they seem to have more issues with the heat cycling.

On 35s a trans cooler is a must regardless

whitexj98 said:

On 35s a trans cooler is a must regardless

Click to expand...

Okay, doing it tomorrow!

Also having a new CPS shipped from a Dodge vendor. Between the two I should have covered my bases.

Did you resolve the issue? I'm having the same problem on my stock 97.

There is a technical service bulletin released by Jeep for the heat shields at the intake/exhaust manifold. It also states to put heat sleeves on your #3 and #5 injectors. I had the same problem for awhile till i installed the heat sleeves on #3 and #5. i have an 01' XJ. 4.56s and 35's, it is also my DD. If i was sitting in traffic on a hot day it would start to idle like crap then shut down. Id let it cool down for a bit and it would start right up and was fine if was moving. If anyone wants to see the TSB let me know and i will post it.

Oh please post that. I have not tested mine yet. It has not had a problem since I replaced the CPS but I have not driven up to Big Bear yet. So far my Jeep cut out everyone I drove up there.