LMM: Fuel Mileage Question

[caseys03duramax]

I just bought a 2007.5 LMM and have gone threw 2 tanks. I averaged 12.7 and that was 70% highway and 30% city streets. Now, the truck is lifted 6 inches on 325/60/18 but I figured I'd see 12-13 city streets and at least 16-17 highway. It's all stock except for the lift. I also have a P0128 code I believe, it is for the coolant temperature. Would that effect fuel mileage? Or is the mileage I'm seeing correct. This is all hand calculated. Also would the mileage go up or down considering I don't know if the speedo has been calibrated. Sorry for the long post.....

The air filter is clean and the DIC says the fuel filter has 93% life left. What else should i look for? I did notice some white haze at idle, but it hasent happened again. The truck is completely stock except for the lift/tires

 

[clrussell]

For a Stock lifted lmm that sounds right on mileage. Efi live delete tune and exhaust would make a big difference..

How many miles? It probably needs a good service regen to clean the exhaust if it lives In town.


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[SmokeShow]

If the mileage/odometer isn't reading correctly for those size tires, you need to add about 10% to your miles per tank and then divide by the number of gallons to refill. Also be sure you are refilling until you can see the fuel at the top of the filler neck. That means you have to shake the truck a bit to burp the bubbles out and let the neck fill all the way up. Then you will have calculated your most accurate fuel consumption.

To me, your MPG seems a little low. But what is the terrain like where you live? Up and down hills a lot or pretty flat? What do you mean by highway? Highways are 55mph zones here. Interstates are 70mph zones. Interstate speeds are what I think of and assume you mean by highway travel. Are you going 70mph or 80mph? If you really mean 55mph driving for your highway mileage, your MPG is really low as driving at those speeds for sustained times should yield the best MPG.

As mentioned, tuning seems to really free up some MPG, especially with LMMs.

 

[caseys03duramax]

Pretty flat, a lot of stop and go BS...when i say highway its usually 70-75 mph. i go Monday for EGR/DPF compliant EFi tunes and then im hoping to find someone local that will give me a hand with the EGR/ DPF delete when i get everything in hand. Im pretty sure i can handle it, but its always nice having someone with more experience to help.

 

[WolfLMM]

Normal. Mine is deleted and tuned running on 285s. I average 14.7 in town. And about 16.5 on the highway.

 

[cdbright]

my 08 was lifted 6" w 35x12.5x20s and with about a 100 HP tune and straight exhaust and bank cold air intake i would get damb close to 20 mpg on the freeway staying under 70 mph, the biggest thing is get rid of the stock exhaust (the DPF and CAT) and you will notice a huge millage increase.

 

[SmokeShow]

Where are you located?

 

[caseys03duramax]

Just outside of chicago