98 4.0 loping

[ReftonsRed]

I just got my 98 w/ the 4.0 on the road again (it had sat for 4 months). On short (15 miles or less) it runs great but on longer drives it doesnt. When I am cruising with the throttle at a constant level it is fine but the problems come when I let off. When I let off the motor lopes and drops down to 1k rpm every two or three seconds then surges again afer a few seconds at 1k rpm, even though i have not changed how much gas im giving it. When this happens if I pull over and shut it off for 5 min it will run fine for a few min but then continue to lope after a few min of driving.
Any help on this would greatly be appriciated as I need to make some long trips pretty soon.

 

[birchlakeXJ]

Try cleaning the throttle body and you may also want to consider testing or swapping out your throttle position sensor to see if that helps....

 

[ReftonsRed]

I replaced the TPS about 6 months ago but ill clean it up as well as the throttle body

 

[ehall]

I had that problem on my Cadillac and eventually traced it down to incorrect timing

 

[birchlakeXJ]

Base timing is not adjustable on the Jeep 4.0

Did you replace the TPS because of these symptoms? If it isn't the TPS, I'm still thiking it could be related to a sensor of some sort. I don't have access to my FSM right now. I'll snoop later on and post back if I find something.

Another thing you could check would be fuel pressure at the schrader valve on the fuel rail. Doesn't sound like a classic symptom of a weak pump but you need to start eliminating possibilities and it's easy to check.

 

[ehall]

Well there are lots of things that can affect timing, such as worn distributor gear, stretched chain, etc.

 

[ReftonsRed]

i ended up taking it to my friends and he hooked it up to see what codes it ran and no codes related to this problem came up (a few other good ones though) Ill try what you guys said then check back