I've got a 1999 Jeep Grand Cherokee Laredo w/ 4.0L
Well- I'm almost at wits end with this WJ-
I'm back at ground zero with my original problem. Hard to restart after gaining running temp; situation slowly deteriorates while running to the point where it will eventually start miss firing and shut off.

It sometimes throws a code- when it does its reading mid fire on #6 with a blinking check engine light.

I've invested over 1500 in parts and now labor to no avail... the money I had for lift and tires is now gone just trying to make it go A to B

parts replaced thus far:
- Crank sensor
-Cam Sensor
-Throttle position sensor
-Idle Air Controller
-Fuel injectors (upgraded to 4 hole)
-Spark plugs (First to stock coppers, then advised iridium to burn hotter plugs)
-Coil pack rail

***all these items ALL created a fault code once before which is why they were replaced***
-Replacement heat shield over intake manifold
-Heath shield around #3 & # 4 injectors
-Fuel filter

-right turn signal blinker fluid
....
yea- EVERYTHING

 

What is fuel pressure like when these symptoms occur ?

 

I'm thinking plugged secondary catalytic converter. The round one under the passenger's seat. It has no 02 sensors on it and won't set a code. It's probably running hot and back-pressuring the whole system. Try removing it and see what happens.