Originally Posted by whitef2504x4
I'm having an issue with my 6.4 powerstroke losing fuel mileage every so often. My truck averages around 26+mpg at 52mph and 21 mpg at 65mph, 15.8 total average with city driving/20.5 on long trips. i normal hit my reset button when leaving on long trips just for the heck of it. I noticed 2 weeks ago on a hunting trip my fuel mileage dropping quickly just after reseting. i was getting only 9.6 -11mpg on the freeway. i thought it was water due to the cold weather at 1st/ so i stop and drained the separator, after doing this twice my fuel mileage returned. A few days later same issue/ same fix. i changed both my fuel filters but had same issue a few days later. After trouble shooting some more i found that just turning my truck off once or twice would fix the problem, i've even turned off the key while driving and resolved the issue. Problem will also resolve itself after 15-20 miles of driving but seems to happen every 60-100miles and averaging 6mpg on the way to work every few days is starting to piss me off. Engine hot or cold or weather hot or cold, loss of fuel milage and a slight power and boost lose will occur. No check engine or regen indicators coming on. Dealer hasn't a clue what it could be.
It's your truck attempting to clean out the Diesel Particulate Filter (DPF). This is also called a regen. It usually happens every 200-600 miles. If it doesn't complete, then it may just be stuck trying to complete it and not getting enough time. 20-30mins of highway driving once the truck is warmed up should do it.
You can check to see if it is cleaning the DPF (Exhaust) by pushing the "setup" button and then the "reset" button. The system check will run through it's stuff ("Charging OK", etc.). It will display xxx to empty. Right after that it will say "Cleaning Exhaust" or something to that effect if it is in the middle of a regen. The truck has to be warmed up (>140* abouts). My temp gauge is at about 1/3 when my regen can start.
The display scenario above is based on which PCM flash update you have I believe.
I am new to all this as well and learning quickly. My last regen wouldn't complete because I only drive about 15mins to/from work. I finally road around on the highway for an extra 30mins yesterday to get it to complete. Fuel mileage went up right afterwards.