So I have a 2012 F250 SD 6.7L
typically the way I drive (which is pretty light 90% of the time) I get roughly 12-14 MPG based on the average of the display in the in-dash readout.

Yesterday when I pulled into work I noticed the check engine light come on. When I left work it was on and I drove home thinking I'd take it in the this morning. of course when I went out this morning it was off so I didn't bother.

I reset the MPG read out avg inadvertently but notice now I'm getting like 8.8.
It seems to run fine and the only thing I notice is when I'm sitting at a stop light that MPG readout is just dropping like a rock. by about .1 MPG every couple of seconds. Now I know after a reset it's got to rebuild it's average so it's sort of off until you get a decent amount of data for it to create a new one. Even taking that into consideration it's never behaved this way before and I've owned it for about 2 years.

 

Any time you get a CEL there should be a code that's stored in memory providing you didn't clear it regardless of the CEL still being on or not.

 

Ok, I'll get it in then. Any clue as to what would cause a fuel inefficiency change like that?

 

Have your fuel and air filters been changed on schedule and are they OEM? Just a WAG on my part.

 

It might be benificial to manually check you actual milage. Sometimes the computer mileage can be erratic. While I watch my computer calculations, I always cross check it manually. There is some degree of variation every time.

 

There are several sensors that the computer uses for calculating the amount of fuel that the injectors shoot into the cylinders. I have no idea exactly which ones or how many but it could be any of them sending false signals, like maybe the sensors are telling the computer that you are under heavy load and the engine is making full power all the time?

Who knows, but until a tech gets in there we are all just guessing. You could be stuck in an active regen, or, at least the fuel system may think it needs to feed a regen.

 

x2 to what rushejj said.

Thanks for posting about it and please let us know what happened so we can help the next person that has the same problem...

I got stuck in a regen in the winter (take a bit of time for the motor to warm up when it is sub-zero out) and I was getting 9 mpg until I was able to drive it long enough to clear the regen. I never got a CEL or a drive to clean exhaust filter message though.

Filter changes in these beasts are important as well.

 

Welcome to the forum, raorcutt. I'm glad you're getting your dealership involved; come back and tell us what you find out. How many miles are on your truck? I'll hang around this thread to see when you have any news.

Crystal