I have had the truck for 1 year now. i just replaced the injector pump due to it going bad and also put a airdog II on there as well. the truck has always gotten 13 mpg which is terrible!!! i expected it to go up after fuel system upgrade. it didnt change at all. i then noticed that my temp never went above 150. I changed the bad thermostate... now she runs around 180-190, still 13 mpg... i cleaned the air filter i am totally stumped as i have been told numerous times that these trucks, even duallies with extra low gearing get between 18 and 22. please help i am totally disapointed after pouring thouands of dollars into this problem.

 

Need a little more info on your truck, Gearing, Tranny and average speed. Also is you signature up to date?

 

yes is up to date. it is a 1999 dodge 3500 dually 24v i believe i have 4.10 gears. runs very high rpm 60 70 mph. above 2 grand.

 

Have you tired some of the other things mentioned in previous threads about fuel mileage?

 

16 is the norm for a dually

 

What exactly is your rpm's at 60 and 70. The truck in my sig. at 60 mph is reving 1800 and at 70 is 2100 (similar to yours and gets around 18mpg on the US gal.). That is with 235/85 16's tires. Check to make sure your trans. is shifting into 4th and lockup if not that can hurt mpg.

 

Don't know if its a Automatic or 5-6 speed tranny you have. If automatic you might try running just under 2000 RPM. I have found with my last three cummins, that anything above 2000 rpm just sucks the fuel unless towing and then it don't matter. 2000rpm's with the auto and 4:10's should be right around 69mph. So it won't slow you down to much. If your running a manual, and don't need the big gears you might consider some 3:55's in. My 2000 3500 cummins got 19.5 at 68mph with a 6 speed and 3:55's.

The other thing is the person who rebuilt your VP44 could have set it up to hot. I have a friend that replaced his VP44 in a 2001 2500 that was getting 21 on the hwy with automatic and 3.55's. After the change out he dropped down to 18mpg. The VP44 after that one got him back up to 21.

I getting 20.5 hwy with my current truck at 68mph.

Dave