2001 F350 CC w/140K miles 7.3L. Mods: air intake, 4" turbo back exhaust. ((3-4 years ago)
Only thing I've done differently was used a quart of BG244 last week of September. I have put 12 oz of Diesel Kleen in every fill up before and since. But since Sep, my mpg has dropped from 15-16 mpg to 9-10 hwy!
Fuel filter only has a couple thousand miles on it . . . air filter is good . . . what could be causing this? And no, my driving habbits have not changed.

 

Depending on where you drive...possibility of the winter diesel fuel. If you are where there is a real winter.

 

Are you hand calculating your mileage - That is a big diff. more than just winter blend, seems to me. Did u just start using the DK ? - And u changed the fuel filter after the DK ? Also do u let your truck idle a lot in cold weather ? Truck runs ok & can u check fuel pressure ?

 

Check for boost and fuel leaks.

 

Check out this page:

Low MPGs? Look here first.

 

[quote=A/Ox4;11232428]Check out this page:

Low MPGs? Look here first.[/quote]

That is an other web site that you (we) need to belong to to see. ie... does not work........

 

Hmmm ... Well I also posted it here. I will just have to go find it.

 

I'm definately in a winter climate. Letting the truck warm up for 10 min shouldn't effect it THAT much. Besides, there were tanhks where I filled up, drove highway miles, and then home with similar results.
I don't know how to check fuel pressure.
I've been using diesel kleene for years. Mostly to add lubrisity to the low sulpher fuels we buy.
Fuel filter was changed before the BG244 was added.

 

To check fuel pressure you need an adapter and a Schrader Valve... That will allow you to hook up a fuel pressure gauge to the back of your fuel bowl.

 

Do you have a scan tool or gauge that can monitor exhaust back pressure? I wonder if your EBPV is stuck in a position other than fully open? Does your truck seem down on power?

Other possibilities are that you have a fuel leak. Sometimes the leaks are hard to spot because the fan blows the fluid all over the chassis or it leaks out the drain hole in the engine valley and coats the trans and oil pan without quite making it all the way to the ground.

Here is a photo that shows what the lever positions on the EBPV are for fully open and fully closed. You might be able to use this to compare to your truck and see if your valve is open all the way.

Hope this helps.

 

Wow . . . that's in a pretty remote area but I will look. Looks like that valve is under the turbo?
I'll see if the diesel mechanics at woork can test fuel pressure.
Power and performance is unchanged from before.
I would be less concerned if the changed was gradual, but it dropped literally overnight.

Thanks all.