disappointing mileage in an '05 - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 4 (permalink) Old 12-24-2006, 06:42 AM Thread Starter
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disappointing mileage in an '05

My dad is getting about 14 to 15 with an '05 2wd CC GMC around town. He also pulls a trailer during the week that could run in excess of 18k lbs. However, when pulling the trailer his mileage goes down to 9 or 10. When I pull that weight I get about 13 to 14, and around town empty I am getting 20+ (w/ '02 LB7 zf6).
What is the major difference here? I am 4wd and he isn't?? I have 33" MT's and he has 245 michelin street radials.

What can he do to increase his mileage while being financially responsible?? And what is the difference? I know the engine is slightly different, but what gives?

:shrug:
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post #2 of 4 (permalink) Old 12-24-2006, 04:14 PM
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Merry Christmas, mckey73:

What transmission does your Dad's LLY have?

Generally speaking, the LB7 engine gets significantly better fuel mileage than the LLY engine. My 04.5 LLY / Allison consistently gets 15 mpg around town and 9 mpg towing a 14,000 lb fifth wheel.

Much of the difference in mpg is attributable to the differences in the LB7 and LLY engines:

From GM Media, 12/5/03:

http://media.gm.com/servlet/GatewayS...n=3&docid=2080

I'm not aware of modifications that will allow your Dad's LLY to get the same fuel mileage as your LB7, but your Dad may wish to consider these:

1. synthetic fluids
2. modified stock intake (Cold Air Intake (CAI) modification)
3. a good tow tune; ie: Predator 2.02 or Edge EZ


- Steve

2004.5 2500HD CCSB, 4x4, D/A, tow tune, TD-EOC

Goodies occupying space in garage: Corsa full exhaust, Isspro gauges, KB CAI

2006 Tahoe Transport 33WTB; 14,000 lbs.
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post #3 of 4 (permalink) Old 12-27-2006, 02:32 AM Thread Starter
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Thanks for the info! I've heard people talking about lly mileage and just couldn't believe it. He has the Allison tranny, and will be comparing tuners in the near future. I seriously doubt he is going to want to spend more than $500 on a tune and I'm not familiar with either of the ones you mentioned. Thanks for the leads, I'll go shopping and let him know whats what. If anyone has experiences with tow/haul type tunes it would be appreciated.

Buy some beer and have a couple of friends come over on a saturday to knock out some of those mods!! Just recently I put some stuff on my truck that was in my garage for more than a year, now it feels GREAT!!! :bounce:

oh yeah, that link didn't work.
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post #4 of 4 (permalink) Old 12-27-2006, 02:57 AM
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Fixed the link.


Many people have found that the LLY gets lower mileage than the LB7. Why?
It could be the tune GM used to get the better power numbers. It could be the different head design. It could be the EGR system. Nobody really knows...
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