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Old 01-05-2011, 03:31 PM   #1 (permalink)
Blue Thunder 30
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2006 lly bad fuel milage

I have a 2006 gmc duramax 3/4 ton crew cab 4x4. I have a predator with the 65 hp currently installed. Stock airbox and stock exhaust.285 tires. On the highway the best i could get was 15mpg but usually average 14. Towing an empty 20 ft gooseneck stock trailer it dropped to 8mpg. What can i do to increase mileage
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Old 01-05-2011, 04:11 PM   #2 (permalink)
DarylB
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Quote:
Originally Posted by Blue Thunder 30 View Post
I have a 2006 gmc duramax 3/4 ton crew cab 4x4. I have a predator with the 65 hp currently installed. Stock airbox and stock exhaust.285 tires. On the highway the best i could get was 15mpg but usually average 14. Towing an empty 20 ft gooseneck stock trailer it dropped to 8mpg. What can i do to increase mileage
Did you account for the change in tire size?
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Old 01-05-2011, 04:34 PM   #3 (permalink)
Maine Towing
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What speed are you running at? What is the air pressure in your tires? Is that DIC mileage or hand calculated?
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Old 01-05-2011, 04:48 PM   #4 (permalink)
Blue Thunder 30
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Hand calculated.15mpg was at 65 hwy.14 is at 70. Towed the trailer at 65. My speedometer is correct
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Old 01-05-2011, 04:52 PM   #5 (permalink)
Maine Towing
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Wow - do you have any figures without the predator? That is horrible for sure, how many miles on the truck? I am assuming the CEL is not on? By chance do you know the RPM's you are turning at those speeds?
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2006 Chevy Silverado LT 4, LBZ, 4WD, Crew Cab, DRW, 6 speed, spends her life with a 7 horse trailer hitched in the bed.
100 gal Trans-Flo aux tank
B+W Turnover mount, EGR blocked
EFI Live by "Idaho Rob" w/ DSP 5
Lift Pump at 175,000 miles, CP3 at 299,000
ALL ON MOD - credit to GMC2500HD - best $1.29 mod you can get !!!
Air box mod
Wicked hot wife
4" Flo Pro exhaust, down pipe back, cat was stolen by some scrap iron punks That's my story and I'm sticking to it!!!

Official member of the over 300,000 mile club.

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Old 01-05-2011, 04:57 PM   #6 (permalink)
DarylB
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I'd remove the tune, check it then manually account for the tire size. ~3% per inch of height. See if it's the tires or the tune causing the sucking of the fuel!
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Old 01-05-2011, 04:58 PM   #7 (permalink)
Blue Thunder 30
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Same without predator. Turning bout 17 to 1800 at 70mph. I noticed an increase in power but not econ.
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Old 01-05-2011, 04:59 PM   #8 (permalink)
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i am running the predator on 85 and a 5 inch exhaust and i can only get about 15 to 16 on my 06 lly also. Not very pleased with it as well
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Old 01-05-2011, 05:13 PM   #9 (permalink)
Maine Towing
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1600 is the ideal RPM for fuel economy, it starts to drop off after that, I would not think 200 RPM would hurt you that much, but maybe with the larger tires. What is the wind profile of your trailer? Pointed nose? 7' wide? I know when I went to a larger horse trailer, which had a narrower nose, and less wind resistance, I actually gained a MPG, even though the trailer weighs around 3K more than the old one. I keep my pizza cutter tires at 75 PSI on the truck and trailer and it makes a difference, that and I keep my foot out of it, I try not to get above 1700 RPM when accelerating and that helps a lot as well.
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2006 Chevy Silverado LT 4, LBZ, 4WD, Crew Cab, DRW, 6 speed, spends her life with a 7 horse trailer hitched in the bed.
100 gal Trans-Flo aux tank
B+W Turnover mount, EGR blocked
EFI Live by "Idaho Rob" w/ DSP 5
Lift Pump at 175,000 miles, CP3 at 299,000
ALL ON MOD - credit to GMC2500HD - best $1.29 mod you can get !!!
Air box mod
Wicked hot wife
4" Flo Pro exhaust, down pipe back, cat was stolen by some scrap iron punks That's my story and I'm sticking to it!!!

Official member of the over 300,000 mile club.

Proud Member #880 of the 3500 DUALLY CLUB
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Old 01-06-2011, 08:28 AM   #10 (permalink)
k5robnp
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Since you still have the cat on it, it might be getting clogged up from the extra soot from the tune. When i still had my cat on with a banks 6 gun i noticed a slow mileage decrease until i stomped on it and cleared the cat out and that seemed to help a little. Then i went to a turbo back 4 in with no cat and gained about 1.5-2 mpgs at 65-70. I also have 285's. My speedo is about 4 off so you have to calculate your mileage by gps miles unless you have corrected your speedo.
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