Bad Fuel Mileage
 

I have a 99 Cummins 4x4 automatic with 170,000 miles running an Edge Comp Box, 5in straight pipe, and a K&N cold air intake. Its currently sitting on 285/75/16 BFG ATs with the tire psi at 60lbs front and 55 psi rear. I have the 3.5 gears. I'm only averaging about 13mpg (about 320 miles to an 1/8 of a tank). I run my Comp Box on 5 timing all the time but the fueling varies. It doesn't matter if I have it to the floor all the time or I drive like a grandpa it stays at 13 on all of the fueling. When I bought the truck completely stock last year it got about 15 mpg average. I also ran a smarty before the Edge and it still sat at 13. I believe it could use a lift pump and some new injectors but I don't know for sure. I also keep up on the filter and fluid changes. If anyone has any other suggestions let me know. Thanks

brakes dragging?

what is the tire size? I'm guessing you have 4.10 gears...

also what kinda speeds do you cruise at?


your economy is definitely crap...

I get 15.5mpg average city/hwy mixed driving with huge injectors that haze at idle with 4.10 gears and 315/75R16 mud tires...

If I can pull that off without much effort, your truck should be doing far batter...

before aftermarket injectors and turbos, I used to get 17mpg with the same tires and gears.