Lookin for MPG help bowtie buddies...
 

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???

:s:

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:choochoo:

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:argh:

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 :phy:

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. lol so at least ur doing better than that.

mines 25 highway 19-20.5 city hand calculated edge evo chip turned up driving like a egg under my foot

Hello all. Oh the joys of the computer controlled world.and repair shops that can only fix what another computer tells them. Bring on armegedon and fix are world.but while we are waiting, my mileage on my 05 LLY was 12/13 hwy. I put a cold air on it with much change.(was off my 04 5.3, modified the tube).reinstalled factory air tube and moved mass air flow sensor up to the smooth part of the tube, just past the ribbed part. SIT DOWN. I don't know if it gets a more stable reading that far up the tube or what. ARE YOU SITTING? 1248 mile trip 70 mph avg. 25.7334 mpg! Return trip, less wind,cooler temp, different day,??? 28.1:???? Inhibited shift range problems starting now. Dealer says NO SUCH THING. I think I will send their address to the Koreans or Iranians. TARGET ONE.

Please explain your procedure for calculating this. Not saying your wrong or it is not possible but just unlikely.

I'm only getting 15 but I'm gettin a lift pump and efi soon and hopefully that gets me in the 20s

Miles I drove according to the odometer devided by the gallons of fuel I used. Started with full tank, finished by filling the tank. I told you to sit down, because I almost fell over.

Have you looked into a gear change? Even though you've adjusted for the tire size in the programming. You still have the mechanical issue of the gearing. Most of the common sites that sell ring gears and pinions have formulas that will calculate the size tire your running or want to run and tell you what gear you should be running for that size tires. All these guys have made good modifications that will improve mpg's and performance. But sadly once you put 35"or bigger, you've maxed out the programmers ability to compensate. In most cases...
This is kinda of an old school answer but the method still applies. Hummers came with 37's and their geared 4:10 from the factory. Just saying... It would take 4:56 gears for tires in the 37" range to bring your rpm's back to what they were with factory tires at cruising speeds. This isn't the plug and play fix you were hoping for. But it should improve your mpg's and reduce the stress on the drivetrain. You would need to calculate for the 35" should be between 4:10/4:56. I was recently looking at gear changes for 37" tires....sorry!
Don't know about moving the air sensor couldn't hurt to try.

MPG Help
 

I have a 2005 2500HD 4x4 with the torsion keys turned up in front, I'm running 285/75r16's on stock rims. I have a Ranch highboy camper shell on the back. I have an edge juice with attitude programmer, EGR delete, PCV reroute, K&N cold air intake, 4" exhaust from Cat back, a high flow Cat, no muffler, a Kennedy Diesel single lift pump, and on the mileage tune on the programmer driving it easy all freeway driving I can get at best 23mpg hand calculated. I drive over 4000 miles per month in this truck with all my test equipment loaded into the truck with me the truck weighs in at 8195 pounds. now this is at 1450 rpm's wich with the 5spd Allison is 50mph, with the 6spd Allison is around 62mph depending on gearing and your setup. I am in the process of testing a few theories on how to make this better, and if they work out, I will post them here. I have 236,000 miles on my truck right now. Hope you find this information helpful, happy hunting!