ragster1

Hello to all,
I am in need of some advice concerning the” service engine soon” light problem that seems to plague the 4.0 liter Jeep Cherokee. I have owned a 2001 Cherokee with the 4.0 liter, automatic, 90,000 miles. for 2 years. The service engine soon light goes on (over 50% of the time) when the car is slowing down (at intersections, turns, etc). The OBDII reader always shows P0301, P0306 and sometimes a P0300 code. Sometimes the engine light will blink then go away upon acceleration (no codes show up), sometimes it will go into limp mode, sometime it will stay on (showing the codes above). The problem started when the weather turned cold (I live in PA). To date I have done the following:

1. Decarboned the car with the MOPAR product
2. changed spark plugs to Champion Truck plugs
3. replaced coil pack
4. replaced cam shaft position sensor
5. searched for vacuum line leaks
6. reset the computer (to relearn driving pattern)
7. checked compression on all cylinders (over 135 psi on all)
8. changed oil and filters, automatic transmission fluid, etc
9. removed, cleaned injectors and fuel rail and put new o-rings on fuel injectors (moving injector 1 and 6 to 3 & 4 position) - still shows the P0301, P0306 codes.
10. Changed to higher octane fuel

When weather turns warmer planning to check wiring harness for a short, testing the oxygen sensor, etc. Any other advice to address this annoying problem is appreciated.

trapper

in line fuel filter?