I just picked up a 1999 Dodge Ram 3500 dually.
apparently I didn’t get as good a deal as I’d hoped.
i got it a few days ago, and it’s been running great.
but now it’s kind of stuttering. Usually at highway speeds, rpms at between around 1700-2000.
it feels like I back off on the throttle a little, but if I floor it at that point it seems to respond fine. I haven’t had it do it at higher rpms, around 2200-2300.
i replaced the fuel filter, and the old one was pretty clean. Didn’t fix the issue.
many advice on what to try next?
it has 203,000 miles, and the owner said he replaced the lifter pump recently.

 

What engine/trans?

 

24 valve 5.9 cummins
5 speed manual transmission

 

Fuel filter means diesel. Anyway, you are losing fuel pressure. Have the injector pump fuel pressure checked or do it yourself with a gauge connected to the fuel shrader valve at the filter housing. Chances are it's low and the IP is going out. That's probably why the lift pump was just replaced. If they didn't do the IP also, that's your next fun job! Good news is, it's only a few thousand for the pump. Labor is extra. Sorry, man.

 

Thanks for the not so great news.
i seem to remember him saying he replaced the injector pump as well ( that what the IP is right?)
I’ll double check with him tomorrow.
If it has been replaced, what’s next?
could it be the fuel pump?

 

If the IP is replaced already, it should be alright. The lift pump is the fuel pump. The IP is the injector pump which pressurizes the fuel for each injector and is electric. The IP is cooled by the fuel it pumps but when the lift pumps go bad the IP will cook itself and the electronics die. At least check your fuel pressure to see if the IP and LP are running okay. Is the lift pump in the tank or where? Might also just have a leak in the air to air or leaky injector.

 

Thanks for all the replies.
I haven’t got a hold of the seller yet.
but i checked the pressure at the shrader valve on top of the filter canister, and it’s around 15 at idle, and around 11 at 2000rpm.
there is no shrader valve on the injector pump that I can see.

Where fuel line comes into IP

I added a picture of the IP

 

Ez edge tuner might be the issue.
maybe i should remove it?
not sure how.

 

Honestly, we aren't a Cummins-heavy forum. There's actually one where you will find many more qualified helpers called "Cummins Forum." I suggest you ask them about the tuner and what else could be causing the hesitation.

 

It could be. I got a Furd Powerstroke in a trade once that ran great, until it didn't. My neighbor is a diesel mechanic and he couldn't figure the trouble. All he could find was a possible bad wire so I towed it to a specialty electrical shop. 3 hours to find the problem, 3 minutes to fix it. The truck came from California but had a Federal chip installed. Eventually, it freaked the computer out and it wouldn't talk to the diesel driver. Hence, no run. They unplugged it and it ran like new.

Try asking here for some help.

https://www.dieseltruckresource.com/forums/

It's similar to here but heavy towards oil burners. I used to go there regularly before I found this place. They tolerated my rather....unique, sense of humor.