TheDieselPage.com Forums
 
The Diesel Page Forums

2019 - TDP's 23rd Anniversary
What's New | Feature Articles | Product Reviews | Member's Area | Free Forum Registration
Duramax 6600 Diesel Page | Advertiser's Section | Classified Ads | The Diesel Page - Publications


Go Back   TheDieselPage.com Forums > 2001-2019 Chevrolet & GMC 2500HD/3500 Light Trucks > Duramax 6600
Register FAQ Members List Photo Album Mark Forums Read

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.

Reply
 
Thread Tools Display Modes
  #61  
Old 06-24-2008, 05:21 PM
AKMark AKMark is offline
Building another 6.2L powered vehicle
 
Join Date: Dec 2006
Location: North Pole, Alaska
Posts: 400
Default

Those tires are pretty heavy, that makes a bigger difference than most realize. Also, how far off is your speedo now? Make sure to take that into consideration.
__________________
05 2500HD CC LB LLY, 4x4, 3.73s 235/85R16's, webasto cab heater, to keep it warm.
03 Buick Rendezvous - When you average over 80 miles per day driving around, you need one of these.
85 K-5, 6.2, SM465, Rockwell T221, 1 tons, 36's. More goodies to be installed as time and money allows.
82 K20, 6.2, SM465, NP208, stock except for bed rack, snow plow, and glow plugs are on a toggle switch. It works great for plowing!
72 Postal Jeep - Yet another project
Reply With Quote
  #62  
Old 06-25-2008, 05:49 AM
leolkfrm leolkfrm is offline
Enthusiast
 
Join Date: Mar 2008
Posts: 79
Default

The lift kit won't affect as much as the tire size, With 373 rears and adding bigger tires the allision computer starts changing things, sensing the load from the tires it adjusts to more of a tow mode, changes the shift points and converter lockup.
I know of a truck with 22.5's that won't go into full over drive lockup untill 25mph because of the matchup of tire to rear end.
As always it takes a diesel a long while to break in compared to gas. It took about 17000 mi to notice a dif in my cat330
Reply With Quote
  #63  
Old 06-25-2008, 12:07 PM
Ric Ric is offline
Enthusiast
 
Join Date: Jun 2008
Posts: 15
Default

Quote:
Originally Posted by craigth View Post
If I were to do it over again, and especially with the $2.99 for 3yr gas purchase promotion, I would check out a Dodge Cummins.

I agree that in my case the speedo and odometer are probably not accurate due to the larger wheels but. hand calculating nets the same piss poor 10-11MPG. Larger tires should NOT make that much difference in MPG vs stock tires! With the Duramax I should be getting at least 13-15 if not higher considering some on this forum claim 17-20, which sorry, I don't believe!

I did find cool product that I would like to try. It's a solenoid operated exhaust bypass. I think the gas mileage issue in these Duramax's is partially related to all the smog crap they put on in the exhaust. Check out http://www.streetpro.us/PowerMasterPics.html
I really don't know. I think if your tires are 10% larger than stock diameter, that affects the circumference greatly (10%) and hand calculating cannot make up for that. Let alone the electronic thinking the ECM and allison are doing for you.

For instance, the DIC on my 6.0 1500HD 4x4 reads "average" 10 to 11mpg if I let it figure over 3-4 tankfuls of normal home and business driving.. My tires are 305/70/16 Wranglers and I guess they are about 10% larger than the toy tires which came stock on the HD.

I cannot speak for the innacuracies of the DIC regarding gallons used because I doubt any of us know for sure we get an exact gallon at EVERY pump or not, so that's another variable.

I do agree that I expect more than 10-12 mpg or I'll just keep my 6.0HD.........
Reply With Quote
  #64  
Old 07-18-2008, 03:52 PM
vsp114 vsp114 is offline
Newbie
 
Join Date: Mar 2008
Posts: 1
Default

2008 2500 HD crew cab, long box bought in March, don't drive it much yet, but with about 5,000 miles, getting between 17.54 to 18.81 hand calculated. Mixed driving.
Reply With Quote
  #65  
Old 08-22-2008, 07:08 PM
mesam57 mesam57 is offline
Newbie
 
Join Date: Aug 2008
Location: TN
Posts: 1
Default 2008 2500 HD 4x4

Just took delivery. 1 tank so far. Dash shows 14 - 16 in city. Highway driving can be good or bad; Seems the truck likes to run about 68 - 70 mph and 1800 rpm's. Running here the dash shows 22.6 mpg. Push the speed above 70 and 2100 - 2200 rpms and the mpg drops to 17 - 18 mpg.

I read about the priogrammers and the results don't seem to justify the cost.

I here (rumor) that the 2008's have a tattle tale in the on board computer. Do theses things void the warranty?
Reply With Quote
  #66  
Old 09-02-2008, 04:18 PM
Ric Ric is offline
Enthusiast
 
Join Date: Jun 2008
Posts: 15
Default

Well I bought the 08 Crew Cab short bed 4x4 chivvy with Duramax

Riding home the DIC calculated 22mpg with 1hr of freeway only driving... round town averaging with that freeway run over the next couple of days, the DIC is calculating 14 to 15mpg... Dunno bout the accuracy til I do some hand calculating to check GPS speed to the truck speedo and then hand calculate MPG...

I need to study this site more to find out about all the programmers etc because I do intend to run 305 70-17's on this truck

By the way, what is with the cooler thingy for the fuel being down near the ground in front of the fuel tank with no protective skid plate?
Reply With Quote
  #67  
Old 09-03-2008, 11:14 AM
Sivrug2 Sivrug2 is offline
Newbie
 
Join Date: Aug 2007
Location: S. Texas
Posts: 4
Default

There is a tattle tail feature on the LMM's that keeps track of the programming/flashes. This was relayed to me by the shop foreman and friend at the local GMC dealer.
I recently did a turbo back exhaust and installed a "Spare" computer that was programmed mild upgrade/tow.
Hand calculated my mileage in town is up 1-2MPG on the highway 5-7 MPG increase.
Reply With Quote
  #68  
Old 09-05-2008, 08:38 AM
Ric Ric is offline
Enthusiast
 
Join Date: Jun 2008
Posts: 15
Default

Quote:
Originally Posted by Sivrug2 View Post
There is a tattle tail feature on the LMM's that keeps track of the programming/flashes. This was relayed to me by the shop foreman and friend at the local GMC dealer.
I recently did a turbo back exhaust and installed a "Spare" computer that was programmed mild upgrade/tow.
Hand calculated my mileage in town is up 1-2MPG on the highway 5-7 MPG increase.
will the tattle tale feature void my warranty if I install one of these programmers ?
Reply With Quote
  #69  
Old 11-03-2008, 09:42 PM
SlimWallet SlimWallet is offline
Newbie
 
Join Date: Nov 2002
Location: Littleton, Colorado
Posts: 8
Default Mileage

New 2008 GMC 2500 DC Crew cab....Colorado

First tank....mt, mixed town and highway.....16.2 mpg

Second tank.....mt... up the mountains to go fishing...mostly highway and 70 mph.....17.4 mpg

Hand calc'd

Slim
__________________
2008 DMAX, 4wd, LB, CC
SRW, 265/70/17
Reply With Quote
  #70  
Old 11-04-2008, 08:34 AM
Duramaster's Avatar
Duramaster Duramaster is offline
GMC World Class Technician
 
Join Date: Mar 2007
Location: Pacific Northwest
Posts: 735
Default

The ECM is supposed to keep track of the last 10 program reflashes.
__________________
1998 Chevy k-2500 454 147,000 miles and climbing!

1993 Pontiac G/A Big Block 3.3 Liter 140,000 miles and still going too!
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -7. The time now is 06:05 AM.


Powered by vBulletin® Version 3.8.2
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright 1996-2019 by TheDieselPage.com - All Rights Reserved