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I now have a little over 9,000 miles on my 04 LB7. After about 6k miles the mileage started dropping and dropping fast. I was getting anywhere from 16 mpg to 19 mpg with mixed city and highway driving. It started dropping and finally got to averaging around 14 mpg. I thought the fuel filter might be the problem so I changed it. Ran down the highway last night at 65 - 70 mph with no wind and got 13 mpg.


I am not running any mods and haven't changed the truck any but I did switch oils from Rotella to Delo at about 6k miles.


Any ideas as to why it has worsened so much? The truck still runs great.
 

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are you goin by the dic or doin the math to get your mpg? the Instrement cluster has always be off on mine
 

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on a short wheel base(26 gal tank) i been getting 350 to 380 miles per tank.....
 

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I've been hand calculating and using the DIC and they're usually within 0.1 - 0.2 mpg different. What's worrying me is the drop in mileage. If i never got 16-18mpg it would be no big deal.
 

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Air filter? Plugged filters cause the engine to starve for air. I don't trust the sensor, just pull it and look
 

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My range is bang on with rickles04. I'm averaging about 17 mpg and am always running about 9000 lbs.
 

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Step 1: Remove foot from floor with pedal under it.


Step 2: Watch fuel mileage increase again.


Step 3: Smile that fuel mileage increased.


Step 4: Frown cause you are going so slow now.


Step 5: Say screw it, push pedal to floor, deal with mileage and smile again......
 

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I notice that my mileage drops off in the winter due to the fuel remix that stations do to prevent gelling, maybe you got a bad batch of fuel. I would also check all of the above.


JP
 
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