04 Duramax LLY

[tricky]

I have an 04 Duramax with the LLY motor and was expecting better gas milage 15 at 80 and more power. After calling Edge they told me on their dyno that the new motor had 30 ft lbs torque and 10 hp less at 50 to 80 mph than the earlier motors. Since then I have installed the juice edge with the attitude and the Banks Monster 4" exhaust system. The cat is gone also. The power is great and I have not check the mileage with the exhaust. But with the chip it was still the same. The truck has 2500 miles. The fan also run alot when pulling. Is everyone experiencing this.

[More Power]

15-mpg at 80-mph... There is no free lunch... Speed kills - fuel economy.

If fuel economy is important, I'd drive a little slower. I predict there could be as much as 5-mpg difference between 65-mph and 80-mph.

Edge ought to know what the new trucks are dynoing at, but we know the LLY did a good job at this year's Pull-Off (http://www.thedieselpage.com/features/pulloff04.htm). Top speeds attained on the hill compared favorably to the LB7's we ran last year even even though the trailer we used this year was nearly 2K heavier.

Fan-clutch engagement is a good thing. Not engaging when it should is a bad thing. It engages when it sees an increase in the airflow temperature that requires more cooling. Generally, running A/C, warmer Allison ATF temps, and/or using more power (hotter intercooler or increases in engine temp) will cause the fan-clutch to engage. While we know that fan-clutch engagement consumes some engine power, not engaging could result in overheating and a total loss of power (pull over to let things cool, etc.).

MP

[Brad Pelot]

I have heard similar things from a couple of buddy's that have the lly, although they get about 16 to 17 mpg on the road.
I have had two lb7's since 2001.They both get 18 to 19 at 80 mph.

[Buck]

My LB7 falls off sharply over 70 mph. 1900 RPM seems to be the "sweet" spot on my truck, gets 19-20mpg running that.

Hopefully, the LLY will be similar ;)

[RdTxTd]

With a new '05 LLY, I got about 21 MPG on a about a 120 mile round trip on the highway, according to the DIC - which I realize may not be extremely accurate. That was travelling between 45 - 55, 4th and 5th gears. Still getting it broken in.

Dave

[More Power]

As a general rule of thumb, light-truck diesels produce the best fuel economy when run at the engine's torque peak. This was true for the 6.2/6.5 and is true for my experience with the Duramax. There is an rpm window of a couple hundred rpm, around which will still deliver excellent fuel economy.

The LB7 torque peak is at 1800 rpm and the LLY at 1600.

I'd recommend people run some experiments with their own truck, with fuel economy runs at, below and above the torque peak. The LLY is different from the LB7 in that it uses different programming, turbocharger and emissions controls. Where it delivers the best fuel economy might not be where the LB7 does.

MP

[dmaxmule]

I got 20.68 mpg out of a 2005 lly @2100 rpm. This was on a 400 mile trip. At the beginning of the trip the truck only had a little over 500 miles on it.

MPG has went down since then because I enjoy the power too much; however, the current tank appears to be very high. The current tank is also the first tank of premium deisel. All other tanks were regular #2 from BP. I will try to let you know the mpg of this tank.

thanks dmaxmule

[silverback]

My milage (early 04 LB7) improved dramatically at around 10,500 miles. I was really surprized becasue I was towing at the time. Seems to be getting around 18 Mpg non-towing. Which is unadjusted for larger then stock tires. So It's probably around 20 Mpg.
Ken

[rickdlance]

My 2 LLY's get 25% less fuel mileage straight across the board, towing or not. This is comparing them to 3 LB7's. My 2 2001's would get 18-20 mpg at 80 mph. I am lucky to get 16 with either of the LLY's.

[Mile Hi Guy]

I am in the same boat as Rick. I get 1.8 - 2.0 mpg better driving a 6.0 Denali verses mine with the same routine. :mad:

I hope somebody figures out why some of the LLY's are well off the mark!!

[rdanley]

i think i have found something in my truck that increased the mpg. last night i went to change my air filter over to the amsoil filter. in the process of changing i noticed between the air box and fire wall that on the wall thier was a pice of aluminum with a rubber sticky back.attached to the fire wall have of it was lose and being sucked into my air box cutting of the air supply why that was thier i do not know because it was also covering up the intake holes on the wall. anyway i got rid of it and installed the new filter this morning i got up and went 200 miles up to blackwell okla running 78mph and i was showing 16.5mpg but on the way back i was running 80mph and got 13.9 that was also with a south head wind. but proir to all of this i would get 13.0mpg know matter what. i also have just completed a 3k trip with a 16k fiver on back and got 10.3 mpg.