I have a 1998 Jeep Cherokee with the 4.0L I6. It had a problem where intermittantly it surged and sometimes backfired on acceleration. The more the throttle was depressed the worse the symptom became.
When it first started doing this I discovered that the fuel pressure was sometimes as low as 20 PSI. I changed the fuel pump/filter assembly and the problem disappeared for about 2K miles.
It has now come back but only on moderate throttle. I have checked the fuel pressure at the fuel rail and it appears to always be approximately 50 PSI.
This time the symptom is slightly different. If full (or almost full) throttle is applied during acceleration it accelerates properly and will then continue to run fine under all conditions until the next time the engine idles for an extended period (like at a stop light) or ran at very low throttle for a while like when in 4WD on level but rough surfaces such as a field or if the engine has been turned off.
It appeared that maybe the IAC solenoid was sticking open. I cleaned the solenoid and the the IA port. Again the problem went away for a few days then returned. So I changed the IAC solenoid. This did not change the symptom.
So, as it stands, I have a new fuel pump and fuel filter, a new IAC solenoid and a new rear oxygen sensor (changed for another reason). I still have the problem.
I had the codes read and they didn't show anything.
Wednesday, September 5th, 2007 AT 5:37 PM