Poor Fuel Mileage

[7.3Outlaw]

My 02 7.3 has been getting pretty bad fuel mileage and im not sure why? what could be some possible causes? I hand calculated the mileage to be 12mpg. The onboard computer is telling me 23mpg?

Heres a little about the truck if that helps. 02 7.3 crewcab long bed single rear wheel. Has AFE stage 2, mbrp 4inch turbo back, superchips max micro tuner on tow safe mode, Toyo Open Country AT 285/75/16

Thanks
-Matt

 

[RJM06590]

When did it start getting worse mileage? The onboard computers are nicknamed "lie-ometers" so I wouldn't go by it. Your mileage typically goes down in the winter.

 

[7.3Outlaw]

I would say within the last few months or so. I used to be able to make a quarter tank last me a week and now it uses little less than a half a tank in a week.