Is ok 4.5-5 mpg for cummins isx?

Your posting this under new drivers section?

 

Try thread cummins ISX technical discussion page #12 will help you get started?

 

Could of just answered the question. Maybe he is a new driver?

My ISX was doing the same thing. Ended up being a clogged DPF filter and a poor performing dozer injector. Back up in the high 6's low 7's in mountains. In the 8's on the flats of Nebraska.

 

When did this start ?
Since you've had it?
Or recently..

If it has been like that since you bought it...why did you buy it?
I agree there is probably something wrong.

 

How heavy are your loads typically ??

Where do you run mostly, stop and go northeast ?? Out west pulling mountains ?? Down south where its mostly flat ?? How much city driving ??

How much do you idle ??

What RPM do you shift up ??

What is your driving style like, do you hold it flat on the floor all the time ??


more info please....

 

What specs for truck?, what speed do you cruise?, what geography? (flat land or mountains)

 

Probably a 2009 that has never had the DPF removed and baked clean.....Cummins calls for DPF service every 250k.

 

You never know what the owner before you did to the engine as far as "performance enhancements". "Buy my chip, add power and increase fuel economy!" LOL

You say everything "works perfect" ... you mean you can pull 80k over vail pass in 9th gear? If so, there's your problem. Power/torque comes at a cost in fuel burn.

Often, these "performance boosters" do nothing to add power, but hurt fuel consumption drastically. Could have the "wrong" turbo installed, could be a lot of things. My guess is the engine is no longer at manufacturer specs due to some "super-mechaninc trucker" before you. If so, the cost to correct may be more then any fuel savings you might realize in the short term.

 

lot of questions about his driving habits, but not one question regarding type of freight.

if he's heavy haul, then he's probably getting about average. if he's flatbedding, he'd get a little better.

i'd be looking at the dpf, and the turbo. one truck i drove went from 4.5 to 5.75 after rebuilding turbo. turbo was just about dead. it was an 05 isx so no dpf to clean.