I need some opinions! I have a 03 6.0PS which i have owned since 04. Last July I had some issues which the dealer could not find an explaination for. They re-flashed my truck and the problem went away. Since this event I have only recently done some long haul pulling. I get 13-15 around town and 18+ running empty on the highway. These numbers are typical since I have owned the truck. However, I am pulling around 6500lb and am getting less than 10MPG. I used to pull 12-1400lb and got 13+ on highway. I can not tell a power difference but am pulling very light. I drive for MPG so it is not driving style nor terrrain causing this. Any thoughts?

 

Are you getting any DTC's (Diagnoostic Trouble Codes)? They can be thrown without a CEL. One of the more common issues is a bad EGR valve, however there are many things it can be. I have seen many complaints on mpg's, sometimes it is as simple as changing fuel filters at the specified intervals (amd using the proper fuel filters).

From Ford:

6.0/6.4 Fuel Economy:
Ford vehicles equipped with the 6.0 PowerStroke diesel are not rated for fuel economy by the EPA. If economy is in question, a boost test should be performed. If boost reaches 22-25 PSI in third gear, wide open throttle under load, then the engine is operating normally and no economy related repairs need to be performed. If not in specs, then the engine will need to be diagnosed--check sensor reading, VGT and EGR operation, fuel pressure and quality, crankcase pressure, intake or exhaust restriction, exhaust or CAC leaks.
Fuel economy will be affected by many factors, including: excessive idle time (one hour equals approximately 33 miles of driving), fuel quality and blend, ambient temperature, driving habits, vehicle use, towing, loads, add-on accessories. Broadcast Message 1271, 4450, 6989

 

As far as I know, there are no DTCs. The truck is stock and I do not own a programmer to pull these codes myself. I have a Ford mechanic checking to see if the last flash possibly turned down the boost on the turbo or altered anything that may have caused this. All filters are factory recommended and the vehicle is serviced on time. I may look into a programmer if I can not find an answer. Can't afford not to get the best MPG possible at $5 a gallon.

 

My 2005 cc 4x4 short bed dropped approx 2-3 mpg when the only diesel available became ULSD. I started using Power Kleen in the silver bottle and it helped a little. After about 8 tanks of crappy mpg, around 11.5 in town empty, I am no longer using the Power Kleen, because I ran out, and I am back up to around 14 mpg in town. I think the EPA really hurt us with the ULSD. Just my .02