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Getting poor fuel mileage

Hello all I just recently bought a 2010 Freightliner Cascadia with a DD15 13 speed smart shift with 3.73 rear ends. At first I was getting 6 mpg which I was ok with but was hoping a little better. Now it gradually went down to about 4.5 mpg and seems to hover around that area. I've only had the truck for a week only did about 9 fuel ups. I generally pull 80,000 lbs thru the mountains. It's in the shop right now getting looked at to see why it's so low. I also wondering if the fuel filter is dirty how bad can that impact fuel mileage?

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Unfortunately this is the trouble with the newer emission trucks. Many times you will take it to the shop and the shop will tell you nothing is wrong. Another person doing the same job with the same exact truck might get 7mpg and you get 4.5mpg and nobody knows why. You can start by doing the basics. If you don't know when the last overhead was done then reset the over head. Check the charge air cooler and if leaking replace. You can also pull an oil sample to see how the engine is running. If your truck was pre emission these three things would most likely solve or lead you to your problem however all bets are off because this is a 2010. If you were getting 6 mpg....which is not really ok, then it dropped right off to 4.5mpg it is most likely an emmision related problem, which you can spend a lot of money and never fix or you might get lucky and get this truck back up to 6 mpg. I wish I wad better advice. If you can't get this truck up over 6 mpg soon I wouldn't keep it. The fuel filters will have a big impact on performance and if clogged really bad will cause the truck to not run or cut out when you put demand on the engine. Just change them because its cheap and easy to rule out.

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This problem happens to all motors not just emission motors and nobody can find the problem. For instance I have 2 diesel pickups same motor, transmission, rears, tires, and same year and I drive them both the same and there's 3 mpg difference between the 2 of them and nobody knows why.

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everyone knows that the older pre emission engines are better. We had a 2010 cascadia with a DD15 and it was an emission night mare. Never again will my husband and I own an emissions truck....NEVER!!!!!

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Fuel quantity valve!! It's $650-700 for the part, but you can change it out yourself. You'll see and feel the difference immediately!

Symptoms of a bad fuel metering valve (Fuel quantity valve)

Rough idle

idle vibration

poor mileage

inconsistent loss of power or surge at low speeds

inconsistent loss of power

inconsistent flutter sound at idle

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Try checking the crankcase pressure regulator for blow-by. That will tell you if your rings are bad or That there's a bad cylinder or two to deal with, or bad head gasket.

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Chad will be eternally grateful.
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