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  1. #1
    Join Date
    Feb 2000
    Location
    Montana
    Posts
    11,380

    Arrow LMM Fuel Economy

    I visited the local GMC dealer today and discussed the first LMM 2500HD crew cab they sold a week or so ago. I had hoped to shoot some photos of that one, but missed it. However, I did get some shots today of an LMM equipped 3500HD chassis cab...

    The owner of the LMM 2500 reported that his first tank of fuel produced 17 mpg while running at Interstate speed across Montana. This owner has owned a number of Duramax powered trucks prior to this one, his LB7's would produce close to 20 on the same trip, and his last Duramax (a 2005 LLY) struggled to produce 15. So, he's happy with the LMM... so far...

    Jim

  2. #2
    Join Date
    Apr 2007
    Posts
    101

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    Quote Originally Posted by More Power
    I visited the local GMC dealer today and discussed the first LMM 2500HD crew cab they sold a week or so ago. I had hoped to shoot some photos of that one, but missed it. However, I did get some shots today of an LMM equipped 3500HD chassis cab...

    The owner of the LMM 2500 reported that his first tank of fuel produced 17 mpg while running at Interstate speed across Montana. This owner has owned a number of Duramax powered trucks prior to this one, his LB7's would produce close to 20 on the same trip, and his last Duramax (a 2005 LLY) struggled to produce 15. So, he's happy with the LMM... so far...

    Jim
    Keep us/me posted I ordered the new body sierra LMM 3500 SRW SLT 4X4 long bed and hope to get it by the end of May.
    Anything has to be better than the 6.0 disaster I had.
    I know it is early reports but "Thanks for the info".

  3. #3
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    Feb 2000
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    Montana
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    Arrow

    Here's a shot of the 2007 LMM equipped chassis cab.



    GVW is reported as being 12K. This one is equipped with dual fuel tanks and 4WD. The exhaust system is equipped with a DOC (Diesel Oxidation Converter) and DPF (Diesel Particulate Filter), but no muffler. Also, the air mixing exhaust tip is a downturn tip ahead of the rear axle.



    The engine looks very much like the outgoing LBZ, except there is now a throttle valve in the intake plenum, upstream of the intake air heater.

    Jim

  4. #4
    Join Date
    Jan 2007
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    115

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    [QUOTE=The engine looks very much like the outgoing LBZ, except there is now a throttle valve in the intake plenum, upstream of the intake air heater.

    Jim[/QUOTE]

    I am trying to compare it to my late production LBZ (12/06). Could you make either a better picture or circle that "throttle valve" please? Ran in the garage this morning and took couple of pictures of my engine compartment to compare it to your pic.
    The only thing that is missing on mine is that silver shielded cable thats fastened along the firewall behind the plastic 6.6L cover.
    07 Chevrolet Classic, CC, regular box, Duramax Diesel, Magnaflow dual exhaust and Superchips tuned.

  5. #5
    Join Date
    Feb 2000
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    Montana
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    GM calls it an "Air Intake Valve", which is controlled by the ECM. The valve is activated during DOC/DPF regeneration, EGR operation and "rich idle".


    Jim

  6. #6
    Join Date
    Mar 2007
    Location
    Pacific Northwest
    Posts
    740

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    What did you think of that downturn pipe just ahead of the rear differential?

    The C-4500/ C-5500 trucks are the same way. Looks kind of scary!

  7. #7

    Unhappy mpg & programmer - not happy with LMM

    I purchased an LMM crew cab 4wd in May. The fuel economy was never better than 16 mpg hwy and 13 hwy city. I lifted the truck and put 33" tires on it and hoped that it was a break in issue. My previous truck, an 03 duramax, would average 15 mpg city and up to 22 mpg hwy empty and 14 - 17 mpg hwy towing, varied depending on weight of load from 7000 to 12,000 lbs. I had an edge juice programmer on that truck. I recently put a Bully Dog Power Pup on this truck, really hoping for some mpg results. Being able to correct the speedo was nice, the truck didn't really need that much more power. No matter what the setting that I have the Bully Dog set to, I am averaging right at 13 mpg in town and 17 hwy. I have a very light right foot, so unless milage would increase with a heavy foot, I am probably at about where I'm going to be. Currently the truck has 9400 miles on it. I really miss my 03 and wish I had stayed with it.

  8. #8

    Default Does GM know about the LMM MPG issue?

    I lifted my truck with a ProComp 6" and 34" tires in Sept '07. You can see pictures in the TDP Photo Album page.

    Interesting that you were able to adjust the speedo as the local GMC dealer said it couldn't be one with Allison transmissions! They also said that I couldn't have the tire pressure sensor set lower than 62PSI. However, a friend of mine with an '08 LMM 3500 said his dealership awas able to lower it in the 50PSI range. Not real happy with the knowledge and willingness to service non-standard features at the dealership.

    Was the tuner worth it for performance? Did it make any noticable difference? Why did you select the Bully Dog tuner over another brand?

    I wonder if GM knows about the LMM MPG issue?! I also wonder if this forum and the members of the TDP could use their numbers to communicate the issue and see if GM can tell us why and/or address the problem with some modifications.

    It's really sad that in this time of high gas prices and diesel technology promoted as high mileage GM can't at least maintain or better yet increase the MPG of their LMM trucks. Most vehicles from year to year increase their MPG not decrease.

    Maybe GM will get the wake up call they need when Toyota producesa 2500/3500 series of trucks with their own diesel! I'm sure their MPG will be high and more than likely the truck features and quality will be superior!

  9. #9

    Default LMM and Tuner

    I went with the Bully Dog because the sales manager at the dealership that I use recommended it. My previous tuner, in my 03, was an Edge Juice. It worked really well, but I did have some stalling problems so I decided to try this one. The Bully Dog does allow you to tune the speedo to your tire size, although I have not checked it to make sure that it really did anything. There is definetely a power difference, although for street driving without a load, I don't really feel that there's a need for the increase. I netted about 1 mpg increase, far below the 3 mpg increase that I realized with my 03 and the Edge product. I would not recommend spending the $500 for that small of an increase. I'll be taking my truck in for it's 10k oil change soon and will talk to the service manager about the milage issue, although I know the answer already that I'll get. It will be "We're not aware of anything wrong"? Always the same answer, until GM sends out a bulletin in about 6 months...

  10. #10
    Join Date
    Jan 2007
    Posts
    299

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    Here's what I have noticed. Each boards mileage claims vary as much (or more) than the mileage I actually get with my own truck. My normal everyday driving I get lousy mileage. Although, I take a lot of short trips and even my longer ones as on So. Florida parking lots (highways). The heat and being at or under sea level doesn't help either. (Doesn't make sense to me, but I get MUCH better fuel economy once I hit the rolling hills of GA and it stays that way until I get back home from Connecticut or in last years case Tennessee)

    Obviously the LMM gets worse mileage than its predecessors, and from what I have expereinced and read it has a lot more power, and a restrictive exhaust too. The best case people seem to say about 1 mpg less and others up to 5-6 mpg less. My LMM gets better MPG than my gas 2007 6.0 Suburban (4x4) and 2005 Denali XL (AWD) and about the same as my 2005 Ford F250, 6.0 DIESEL, 4x4, CC, SB. Which is around 12 in local driving in town and 14-15 on highwy drives, but I drive fast 75-80. And yes, I wish I got better MPG's, but don't we all?
    2007 Silverado, 3500HD, 4X4, CC, Long Bed, SRW, LMM Diesel, Navi, DVD, Roll-N-Lock Cover, ICI Running Boards, CoastalEtech GM Lockpick for DVD/Nav changes in Motion, Back-up Camera...

    2006.5 VW Jetta Special Edition TDI - Blue Graphite - European Spec VW Fact. Nav Radio.

  11. #11

    Default On Board Computer/Hand Calculation

    Here is a few pros and cons in the way mileage is calculated
    When you calculate by hand you have no control over the temp factors,wind,grade to a given point which all effect the rolling stance of the truck. l recently did a calculation using a GPS and the on Board readings. I went 25miles constant speed 55mph pulling a 10,000lbs load the GPS and on Board Computer matched up exactly in distance with an average of 12.5mpg on the Computer. The next day which included some tempature change (5degrees higher) and wind(almost at zero) did the same trip. I got 13.5mpg. The on board PCM calculates the mpg including the wind/grade of road you are traviling on and temp change where calculated by hand you do not include those factors. I also took out a 2008 5.3 l was tuning at my shop drafted a transport on the HWY at 55mph l was amazed watching the onboard compter change from 22mpg not drafting to 25mpg when l drafted the the transport l think the onboard computer are a little moe acurate than we think. It is no secret that the New Exhaust Filter System hiders gas miliage and the amount you can strech the Custom Tune without a Delet of the System. Just my two pennys worth
    Last edited by DmaxMaverick; 04-26-2009 at 20:42. Reason: Email to follow.

  12. #12

    Question 2009 Fuel mileage experiences

    I own a 2006 Chevy 2500 HD Dduramax w/ 31,000 miles. I'm looking at buying the 2009 GMC 2500 HD. I'm not too comfortable buying the new deisels with all of the emmission mandates from the EPA thus having a reduced Fuel mileage than what I already have. I'm just getting 17 MPG in combined City and HWY driving mostly HWY, (54mi HWY, 13mi City).

    What has been the AVG MPG in the new trucks now?

  13. #13
    Join Date
    Oct 2008
    Location
    Cheyenne WY
    Posts
    60

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    Quote Originally Posted by agmakar View Post
    I own a 2006 Chevy 2500 HD Dduramax w/ 31,000 miles. I'm looking at buying the 2009 GMC 2500 HD. I'm not too comfortable buying the new deisels with all of the emmission mandates from the EPA thus having a reduced Fuel mileage than what I already have. I'm just getting 17 MPG in combined City and HWY driving mostly HWY, (54mi HWY, 13mi City).

    What has been the AVG MPG in the new trucks now?
    I have a 2009 GMC Sierra, Crew Cab, 4WD, with just over 3100 miles on it. I haven't had an opportunity to check highway mileage yet, but in-town I am getting just over 14 MPG. As with the other Duramax trucks I've owned, I'm confident the MPG will increase as more miles are put on the truck.
    2009 GMC Sierra, 2500HD, Crew Cab, 4WD, D-MAX
    2009 Chevy Malibu LT, V6
    2005 Jayco 323RKS, 3600W Onan Generator

  14. #14

    Default

    Quote Originally Posted by agmakar View Post
    I own a 2006 Chevy 2500 HD Dduramax w/ 31,000 miles. I'm looking at buying the 2009 GMC 2500 HD. I'm not too comfortable buying the new deisels with all of the emmission mandates from the EPA thus having a reduced Fuel mileage than what I already have. I'm just getting 17 MPG in combined City and HWY driving mostly HWY, (54mi HWY, 13mi City).

    What has been the AVG MPG in the new trucks now?
    Unless you have a very compelling reason to get a 2009 I'd keep your 2006. The new trucks are nice with the exception of the gas mileage. I had a 2002 that got 14-15 City and 15-19 Hwy. My 2008 gets 10-11 City and 14-16 Hwy.

    The other thing to consider is that aftermarket chips/computers are not recommended as they will effect the new emissions equipment.

    2008 GMC SLT 2500HD Crew Cab SWB 4WD ZLT
    Black / Titanium
    Sliding Rear Window
    Integrated Trailer Brake
    Billet Grill
    Pro Comp 6" Lift Kit
    Helo 17" Wheels
    Nitto Terra Grappler 305/70/17 Tires
    Spray-In Bedliner
    Weather Guard Low Profile Aluminum Saddle Box
    Remova-A-Ball Gooseneck Receiver

  15. #15

    Default

    There are no compelling reason other than getting a newer model with the added options and having a newer model before I retire. I like to research performance by asking others on thier experiences to get a better guage on what is going on with the new Truck inventories because the Manufactures and dealers will not tell the truth. I know fuel mileage ALWAYS takes a hit when new emmissions equipment are added I just did not know how much of a hit the new engines are taking. For me, fuel economy is first on my list when making truck purchase decisions.

    Sometimes I think it's done on purpose to kill the deisel engine for other than commercial use.

  16. #16

    Default Disappointed to say the least !

    08 GMC CCSB. Front leveling kit only, 305/50/20 tires(actual height is 32")

    Best tank on highway 14.8
    Avg highway 13.9
    Avg local 12

    Hauled my motorcycle trailer today and got 8.2 MPG. It only weighs 4000 loaded. My 06 silverado with a 5.3 got 10 MPG everytime on the same trip, same trailer.

    Diesel fuel 3.399 gal = very expensive and disappointing.

    All mileage figured by GPS and amount of fuel pumped at the station. The DIC shows worse mileage than actual.

    KD ECM on the way. Hopefully it helps
    2008 GMC Sierra Crew Cab
    Short Bed Debadged.

    -Kennedy ECM
    -Magnaflow 4" Turbo back off road exhaust
    -20" Wheels w/ 305/50/20 Coopers

  17. #17
    Join Date
    May 2011
    Location
    CENTER CONWAY,N.H.
    Posts
    3

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    my 2011 3500HD with the break in oil still in motor at 2560 miles is telling me via the dic that fuel mileage is 14.8 and seems to be climbing during this break-in time. i am going to run mobile devac elite synthetic diesel motor oil. i guess i should start keeping track of mileage the old fashioned way after i dump the break-in oil.





    would like to read about other 2011's
    keep your sawchain tight & sharp,don't force a dull chain to cut.

    [URL="http://www.woodnsaws.org"]www.woodnsaws.org[/URL]

  18. #18

    Default

    Great looking rig...nice chainsaw/logging website!


    www.MREBoatTransport.com
    2011 Chevrolet Tahoe 5.3L daily driver
    • Previous owner of two 1994 6.5L K3500s, '01, '02, and '05 6.6L K2500s, '04 C4500, '06 K3500 dually, '06 K3500 SRW, '09 K3500HD SRW, '05 Denali
    • Total GM diesel miles to date : ~950K

  19. #19
    Join Date
    Jan 2001
    Location
    New Hampshire - Live Free or Die
    Posts
    6,056

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    Quote Originally Posted by crazydave01 View Post
    Diesel fuel 3.399 gal = very expensive
    Ah, for the good old days!
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
    New ride: MB GLS450 - most stately
    Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510

  20. #20
    Join Date
    Jan 2013
    Location
    Wellington Colorado
    Posts
    3

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    I have owned a 2002, 2004 and now 2008 3500 HD. Got 17 to 19 in first two. I have 72,000. on the 2008, got 17 when first purchased, now 12 to 14. When I take to dealer and they reflash I can get 19, this will las for a few tanks of fuel then back to 12 to 14. I can put my auto zone tester on and there will be no codes, I reset codes, even though there are no codes, and I go back to 18. I would like to put an edge cts and an exhaust brake on but would like to figure out what is wrong before I do anything. Dealer has no idea.

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