OK, here is my question. Is anyone with a '04.5-'05 Duramax LLY getting better than 17 MPG? I have an '05 4x4 crew cab silverado with a 6" lift rolling on street friendly (mellow tread pattern) 35" all-terrains with 3.73 gears. The best millage I have ever gotten was 14.8... Under the hood I have modified the stock air box on the side to get more fresh air, changed the stock intake elbow to the AFE elbow, and added a flow thru muffler (got me from 13.8 to 14.2). Added the duramilage programming and went up to the current 14.8 MPG. I also added a PPE boost controller but, it makes little to no change in economy on or off. It does however, make passing WAY EASIER! I drive the same route daily (65 miles each way) driving 70-75 MPH and keep excellent fill-up and milage logs. I have been tracking every tank for the past three years with 14.6-14.8 MPG typical. I am easy on the pedal all the time. I read post of people getting near 20 MPG with LLY's. Can anyone help me figure out how this can be achieved???

 

your biggest enemy is the lift, think of it like this, you drive a brick, a brick gets crappy mileage, what happens when you make a brick bigger? it gets worse

my truck, and LBZ mind you gets 20mpg on the highway, but most of my tanks are in the 16-18mpg because of the short distance i have to drive to work

Im running EFI live with duramaxtuner transmission safe DSP5 tuning, and i run on the 415rwhp tune most of the time and seem to get the best mileage on that tune

 

My 04 LB7 with the same lift and tire size got 18 all the time... I think your LBZ gets beter too right outta the box. Im hoping a LLY guy will speak up.

 

all stock my LBZ got between 13-15mpg

 

I'm thinking my stock LLY gets around 16. 17 maybe. Not totally sure cuz I'm up in Canada and the conversions get all screwed up. Does that sound about right for a stock truck? It sits really low. I don't think the previous owner lowered it or anything but I wouldn't rule out dropping a torsion bar position. (Is that even possible?)

 

yeah it's possible to get a different torsion bar key that will start in a lower position than stock.

I've see LLY's get 20+ mpg. a lot of airflow/exhaust mods, and EFI Live/DSP5. But, a lift, and big tires will definitely bring that down. Wider tires have more traction, more rolling resistance = more power required to roll em down the road.
You really need to look at more airflow mods, and a good EFI Live tune. Get those 3 years of bad mileage back. How are your injector balance rates?

 

Jban, What air mods are you refering to? I've opened up every part of the intake. I don't know of anything more to do short of changing to a bigger turbo. Bigger turbo will cost more than I would ever save in economy. I'm not sure but, I think a 4" pipe going through a flow thru muffler is as close as possible to a straight pipe. I can see that people love their EFI live for the LLY... Could work better than the tuner I already have but, If I'm out another $500 for a tuner that doesn't get me 2MPG over what the current one does it just pissn away money

 

has your odometer been corrected for the tire size? what RPM are you running while at 70-75? try cruising at 65 (if you can) and drive like you have an egg between your foot and go peddle

another thing to try, clean your MAF sensor and change the air & fuel filter

if all else fails, loose the lift

 

Thanks for the reply. Yes, I have the speedo corrected for tire size. I'm turn'in about 2000 at 70 and 2250 at 75. Slowing down to 65 just isn't worth my time... I am super easy on the pedal and try to let it shift under 2000 rpm. Loosing the lift is just crazy talk! It wouldn't look like a 4x4 if it was lowered the way they come from the factory.

 

stock height, stock tire/rims. rest of the mods are listed below. like he said above, a lift kit is gonna to kill ya. my buddies truck is identical to urs height wise. he is running 6 inch lift on his 1500 extended cab with 35 inch tires with a 5.3 gas eng and he gets 12 babying it and 8 mpg riding the pedal. so at least ur doing better than that.