Drastic MPG drop - Diesel Forum

jandoe · 11-09-2008, 12:09 AM

I have been averaging about 12.5 mpg since I purchased the truck a month ago. I have driven 2000 miles and all of a sudden I am down to 8.5. I had her in the shop last week for a couple minor things and Ford did a recal on the cooling system. Seemed ok after that until I filled her upa nd the milage has dropped quickly. There does not seem to be any change in the performance or handling. Idles good and no smoke or nothing. Just a question about what may be the cause.

torino73 · 11-09-2008, 12:53 PM

Hand-calc. or lie-o-meter? That thing is useless. Mine will say 470 miles to empty. Then I'll drive it a few miles, shut the truck off, fire it back up and it will say 478 miles to empty. I'm not really sure how this thing works or how it resets it self, but I do know that heavy pulling or extensive idling throws the numbers into a tailspin. Do a hand calc and see what you get.

1/2tired · 11-09-2008, 02:19 PM

Mine was basically "stuck" in a regen cycle when my mileage dropped off that badly. Drive for a while at highway speed, longer than a 15 minute trip, and then see if your mileage returns to normal. Worked for me, as my local Ford dealer told me that was their first course of repair and troubleshooting.

I wish that i had kept the Technical Service Bulletin that describes the symptoms more accurately, but if you are idling at around 1000 RPM, the long drive technique should clear up the problem for you.

jandoe · 11-09-2008, 06:13 PM

I don't thinks its in regen, normal rpms on tach. I filled up and have drove about 60 miles and it is already down to 3/4 tank. Lie o meter is still dropping every time I drive it. The only difference there is, is the temp down about 20 degrees from what it has been. No towing or excessive idling. Once from 1st to second gear it shuttered a little and kicked in but that has been it.

tjsulli790 · 11-10-2008, 12:17 AM

Quote:

Originally Posted by torino73

Hand-calc. or lie-o-meter? That thing is useless. Mine will say 470 miles to empty. Then I'll drive it a few miles, shut the truck off, fire it back up and it will say 478 miles to empty. I'm not really sure how this thing works or how it resets it self, but I do know that heavy pulling or extensive idling throws the numbers into a tailspin. Do a hand calc and see what you get.

Be happy your truck is making diesel

Actually the 08s are pretty accurate at calculating MPG, compared to the previous years. Now the distance to empty is a strange thing because it seems to me the truck can't decided how much fuel it really has left. I used to drive an 03 Dodge gasser and it did the same thing.

jandoe, I would ask the dealership if they did a reflash on your truck. This may be the cause to the change in your truck. Quite a few people have posted some less than desirable results from having the computer reflashed. Also was your MPG reset? It may take a couple tanks of fuel before your MPG starts to level out.

Hellbilly · 11-12-2008, 12:24 PM

WOW! You get that much milage? I drive 50 miles to work. I fill up Monday Wednesday and Friday. I have the short bed so the tank is around 26 gallons. Around 7 mpg?

Singleshot · 11-12-2008, 01:16 PM

I know when mine goes into regen my lie meter goes from 12-13 "city" to 8 in no time, check the system status and sure enough it says cleaning filter. I make a bee line to the interstate or anyplace I can get highway speeds. Regen lasts about 15 min at ~55mph or better and its done. Mph jumps right back to where is normaly would be when not cleaning.

JK