a friend of mine has a 1997 2500. recently his truck has been running like crud. we changed the fuel filter which was very dirty, but no luck. he says it runs ok at idle, but just off idle it sometimes dies or stumbles like it's going to die. it's worse under load. i know this isn't much info, but i told him i would check. the truck has about 160,000 miles on it. anyone have any idea's? seems to run ok at normal driving

 

A few things to check. There is a screen in the fuel heater that can get clogged. Remove the large nut on the bottom and the bowl, and it, along with a few assorted parts, will fall out. Clean the screen and get a rebuild kit from Cummins. Next is the solenoid switch. Make sure that it is going ALL the way up when the engine is running. Check it by pushing on the rod that comes out of the rubber bellows on the bottom. This rod controls fueling, if it is not all the way up, the truck is not getting enough fuel, especially under load. If the rod moves up, the solenoid is dirty. Remove the solenoid, clean it and put it back, get new bellows from Fostertruck.com, or make one from a bicycle inner tube. You can search for more info on this subject. Another possibility is the overflow valve. Make sure the spring is the correct length, it can shorten over time. Easy fix. I am sure that others will chime in on ideas, but that is a start, at least enough to keep you busy for a day or so.

 

You need to check the fuel pressure. Also, the fuel lines may have a small hole causing air to get sucked in. Timing may have also slipped. How does it start?