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Thread: LMM Fuel Economy

  1. #1
    Join Date
    Feb 2000
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    Montana
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    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
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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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    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
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    Jan 2007
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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
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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
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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
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    Quote Originally Posted by Duramaster
    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!
    I think GM would rather peel up road stripes than torch pedestrians.....If it ever comes to that.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  8. #8
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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!
    The pickups use an exhaust tip that exits under the right rear of the rear bumper. Only the chassis cabs (& medium-duty trucks apparently) get the exhaust tip ahead of the rear axle.

    I'll have close-up pics of all this in an upcoming article, but the tip exit looks way too close to the right rear shock....

    Jim

  9. #9
    Join Date
    Mar 2006
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    44

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    DIC average for dealer delivery was 17.4. My LLY was about the same when I first picked it up.

  10. #10

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    i get around 17 empty on highway and 7-9 towing 7000# 28' enclosed car trailer

  11. #11
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    Jan 2007
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    I hope to see the 17 mpg empty. I got 15 on the way home tonight from the dealer... 2007 3500 CC Diesel, 4x4 Long Bed, SRW.
    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.

  12. #12
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    Mar 2006
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    Enroute to work I reset the avg. fuel mileage on the DIC just to see what numbers would come out. 35 miles of mostly level at 70 mph. 21.3 on the DIC.

  13. #13
    Join Date
    Dec 2006
    Location
    Louisiana
    Posts
    33

    Default I must be doing somthing wrong

    9,000 miles, I have not seen anything above 14.9 - empty. 10 MPG towing 30ft trailer. I have been to dealer twice now. No help there - they have been good about it, but no help. They suggested a programer. I have installed a KN filter and superchip, runing in safe tow. I was told safe tow will offer the best mileage. No change. I checked tire pressure, all is good. I love this truck but fuel prices are going to make me park it.
    (I'm not comparing, but my son has the Ford 7.3 we just drove to NM. About 950 miles - towing a small trailer about 1,000 lbs. Got 29 MPG!!! I wouldn't have belived it if I didn't see it with my own eyes!!!)

    Any suggestions would be greatly appreciated.

    thanks
    Larry
    2007 Chevy, 2500HD, Crewcab, 4WD, LBZ,SWB.
    Larry

  14. #14
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    Jan 2007
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    Larryh1,

    So far I am on par with you.... 29 MPG on a 7.3 is incredible, that has to be a 2wd truck? I could get 22-24 with a 2wd 6.0 excursion (when it actually ran)..
    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.

  15. #15
    Join Date
    Dec 2006
    Location
    Louisiana
    Posts
    33

    Default I must be doing something wrong

    Dakster

    That was doing 70 mph (cruise control), flat level driving with an occasional mountain range. I was enjoying ragging him about how much more comfortable my chevy was compared to his ford, until we figured his mpg. I kept quiet after that.

    I haven't given up yet. I will be happy with 17/19 empty highway,and 11/12 towing. I am talking to a diesel shop for some less expensive ideas. I'm not going to spend thousands of dollars to get 2 mpg more. I also keep checking this board for any ideas.

    Larry
    2007 Chevy, 2500HD, Crewcab, 4WD, LBZ,SWB.
    Larry

  16. #16
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    Jan 2007
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    I hear you... Chevy's definetly have better comfort features... My 2007 Suburban was getting 9-10 in the city and 14-15 on the highway empty/not towing. I'll be happy with 12 in the city and 17 on the highway empty. (20% better fuel mileage). I have nowhere to go but up! I'll get a better handle on what to expect for fuel economy in two months when I drive to tennessee and back.

    You can rag on the new 6.4 Ford's, they get horrific mileage. A buddy of mine traded his 2006 Dodge for a new ford (both are dually's) and gets HALF (6 mpg!) of what the dodge got while towing his car to the races. He doesn't know if he can afford the new Ford because of fuel costs! This new DPF/regen requiement doesn't seem to be very MPG friendly.
    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.

  17. #17
    Join Date
    Jan 2005
    Location
    St. Louis, Missouri (pronounced misery)
    Posts
    203

    Default My two cents....

    I put on the Kennedy 4" turbo back pipe and saw an immediate change in mileage. I went from 15 around town to 16 and some weeks 17. I can get 19 steady on the highway running 70. If the wind is right, I have touched 20 but it is a rarity.

    I too am looking to consistently get in the 20s with mine. It is a daily driver that I use to tow our camper about every other weekend.
    Scott
    St. Louis, MO


    '06 Silverado K2500 4x4 Crew Cab D/A "Big Max" AmpResearch retractable Running Boards, 4" Turbo back Kennedy Exhaust, Kennedy Custom Tune!
    '99 BMW K1200LT "Special K" my other "SUV"
    '07 Salem by Forest River Fifth Wheel Toy Hauler

  18. #18
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    Mar 2006
    Posts
    44

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    17.9 DIC last tank of mostly freeway. 2k miles. DIC said I used 20.7 and I put in 21.2, off about 2%.

  19. #19
    Join Date
    May 2007
    Posts
    27

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    avg 17 both hwy and city. 3rd tank of fuel

  20. #20

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    I have run 3 tanks of fuel through my new 2007. It is the 2500 crewcab. I filled up today and found I got 14.6 MPG on routine and city driving. I was hoping for better, will it get better? Going camping this weekend will let you all know how that goes pulling my trailer...
    Mark
    2007 2500 HD Shortbed Crewcab

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