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Duramax 6600 Welcome to the Internet's first Duramax 6600 diesel discussion forum for the LB7, LLY, LBZ, LMM, LML, LGH & L5P RPO code engines. Tips on performance, fuel economy, troubleshooting and more.

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Old 04-02-2010, 03:06 PM
BMDMAX's Avatar
BMDMAX BMDMAX is offline
11 Second 2 Wheel Crew
Join Date: Dec 2001
Location: Sharpsburg, GA, USA
Posts: 218
Talking LMM Round Trip Report - Atlanta, GA to Loyal, WI

I recently completed a round trip from Atlanta, GA to Loyal, WI to pickup my LB7 race engine from Kennedy Diesel. We burned 105.4 gallons of diesel over 2,137.2 miles for a trip average of 20.27 MPG. The highest leg was 21.0 MPG and the worst segment was 18.8 MPG. All cruise speeds were 73 to 78 with some bursts in the 80's. The 18.8 segment was bumper to bumper rush hour traffic in ATL.

All mileage was hand calculated.

This was with the KD Tow Tune ECM and DPF delete with the KD four-inch exhaust. Everything else is stock on my 2008 LMM. Very happy with the KD tuning on the LMM.

I highly recommend the KD tune for those wanting to bump up their mileage on their LMM.
2002 LB7 D/A 2WD. Suncoast Stage V. KD EFILive Tuned, KD N2O, KD 40 Over Injectors, MDP Custom Fuel System, KD MEGA Filter, BD Turbo

2005 LLY D/A 2WD. KD Headlight Booster, KD 4/5 Exhaust, Suncoast Stage V, KD EFILive Tuned.

LB7:12.8@108 #2 Only 11.92@115.62 #2W/N20
LLY: 471HP & 990 TQ 13.58@100.57


Truck Website

Chasing 11's Video

Go Fast Goodies Powered by Kennedy Diesel

11 Second 2WD Crew Posse Member!! Got Slicks?
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Old 12-26-2010, 05:42 PM
crazydave01's Avatar
crazydave01 crazydave01 is offline
Join Date: Dec 2010
Posts: 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
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Old 05-08-2011, 10:05 AM
Join Date: May 2011
Posts: 3

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.

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Old 05-08-2011, 06:54 PM
Mark Rinker's Avatar
Mark Rinker Mark Rinker is offline
Join Date: Jun 2003
Posts: 5,813

Great looking rig...nice chainsaw/logging website!
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
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Old 05-08-2011, 06:55 PM
JohnC's Avatar
JohnC JohnC is online now
Proud Deplorable
Join Date: Jan 2001
Location: New Hampshire - Live Free or Die
Posts: 5,446

Originally Posted by crazydave01 View Post
Diesel fuel 3.399 gal = very expensive
Ah, for the good old days!
"Need" - Wanting to get someone else's money.
"Greed" (formerly meant what "need" means today) - wanting to keep your own.
"Compassion" - a politician's willingness to arrange the transfer.
-Joseph Sobran

Current oil burners: MB 350SDL, Kubota 7510
Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6
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Old 01-20-2013, 07:50 AM
prairiewind prairiewind is offline
Join Date: Jan 2013
Location: Wellington Colorado
Posts: 3

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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Old 01-20-2013, 07:58 PM
DieselDavy DieselDavy is online now
Join Date: Sep 2001
Location: Ft. Wayne, In.
Posts: 471

Are you hand calculating?
Dave, N9LOV
Member #242
Dave's Diesels:
Sold June, 07 '82 1/2 ton 4X4;340k miles
'97 2 Dr Tahoe, Intercooled,
Kennedy ECM, 4" Exhaust
'02 GMC
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Old 01-21-2013, 06:58 AM
prairiewind prairiewind is offline
Join Date: Jan 2013
Location: Wellington Colorado
Posts: 3

Yes, mostly, I pretty much use this truck for trips, I can look at the fuel guage and the milage and tell what is going on. Last summer I had the fuel system cleaned and they reflashed at the same time. I made several trips pulling a 4 horse slant and got 13, a couple of months later I made the same trip empty and got the same, 13. I went back to the dealer and another reflash and back to 17 to 19 depending on how I drove. These trips are over I70 from Denver to Page AZ. I also have a 30' Montana and when everything is running right I can get 10 to 12 when in my lame mode I get 6 to 9. When I started resetting my codes, even though they don't show up it doesn't make a difference right away but after a couple of hundred miles I can actually feel the truck respond. The truck goes from sluggish to very responsive, you know exactly when it happens
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Old 01-24-2013, 06:38 AM
prairiewind prairiewind is offline
Join Date: Jan 2013
Location: Wellington Colorado
Posts: 3

I was sure hoping someone could let me know if they had the same problems, have tried to reset, anything.
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