*UPDATE*Calling Duramax owners 1st trip with camper bad fuel mileage

[73guna]

I have a 2007 crew cab Duramax LBZ 4 wheel drive.
We recently got back from our first camping trip with our new Wildwood 31qbts. The trailer weighs in dry at approximately 8500 pounds. Loaded down I estimated the weight to be right close to 10,000 pounds.
My mileage on the trip was anywhere from 6.5 to 7.5 miles per gallon.
Fresh oil change with synthetic right before trip, tires aired up to 80 pounds, new fuel filter.
Cruise was set between 65 and 70 miles per hour on the flat in the hills I pedaled it. We had a pretty good crosswind all the way down to our campsite and a little ways back. Once the wind stopped I check my fuel mileage again and it was still within the same range.
On the trip I did have a check engine light come on which was p0401 which indicates low flow in the EGR valve. The same code came up prior to the trip and I remove the EGR valve and cooler and clean them.
Now, before I go on to the Duramax forums and have all the Young Guns tell me to delete the EGR and step up to EFI live programming I would like to get to the bottom of this and figure out what is causing my poor fuel economy.
Just wondering if anyone else has ever dealt with poor fuel economy and what you did to resolve the issue.
If it's something I can check on my own that would be great before I took it to a dealer have a scanner hooked to it.

[K_Charles]

How did you check your mileage, with a penciled and paper or look at some screen? That doesn't seem bad for that speed.

[Lynnmor]

IdaD wrote:

carpetguy2 wrote:
I had 07 cc lb lifted with 35s towing a 34 ft tt and a 40 ft 5ver.Never got that crappy mileage.I towed 65-75. I was getting 12 to 15 mpg
I did remove my cat first and helped alot.
Never threw a code.Then I went with 5 inch exhaust and did a egr black plate and did get efi.It made a big difference.
Then my mpg jumped up about 2 mpg and alot lower egts.
Now I have a lmm dually same set up and still get 15 to 17 mpg towing my 40 ft 5ver

Do you only tow downhill when there's a tailwind?

He must have fuel line magnets!

[blackeyed1]

Long shot, but read on another site a probability of trailer brakes causing the drag problem?

[2oldman]

Your phone is double posting.

[IdaD]

carpetguy2 wrote:
I had 07 cc lb lifted with 35s towing a 34 ft tt and a 40 ft 5ver.Never got that crappy mileage.I towed 65-75. I was getting 12 to 15 mpg
I did remove my cat first and helped alot.
Never threw a code.Then I went with 5 inch exhaust and did a egr black plate and did get efi.It made a big difference.
Then my mpg jumped up about 2 mpg and alot lower egts.
Now I have a lmm dually same set up and still get 15 to 17 mpg towing my 40 ft 5ver

Do you only tow downhill when there's a tailwind?

[carpetguy2]

I had 07 cc lb lifted with 35s towing a 34 ft tt and a 40 ft 5ver.Never got that crappy mileage.I towed 65-75. I was getting 12 to 15 mpg
I did remove my cat first and helped alot.
Never threw a code.Then I went with 5 inch exhaust and did a egr black plate and did get efi.It made a big difference.
Then my mpg jumped up about 2 mpg and alot lower egts.
Now I have a lmm dually same set up and still get 15 to 17 mpg towing my 40 ft 5ver

[73guna]

Not sure what happened with three threads being posted. I'm doing this from my phone, must be a glitch somewhere.
Hopefully a mod can merge all three together.

[2oldman]

MudChucker wrote:
Cruise burns fuel... Lots of it.

Please explain.

[the_bear_II]

I have a 2007 C4500 Crewcab Longbed dually 2 wheel drive with the Duramax/Allison setup. I pull a 15,000lb 5th wheel. I average 10 MPG but I usually have the cruise control at 60MPH. When I set it at 55MPH the MPG jumps up to 12.

I only use about 3/4 throttle on hills down shifting to lower gears as needed to prevent the engine from lugging.

Did you verify the mileage manually or go by an electronic indicator. The factory fuel use meters are notoriously off; some by as much as 5 MPG.

Slow down you will be amazed at how much better the MPG are. Enjoy the scenery...smell the flowers.

[73guna]

Cruise control will definitely burn more fuel in the Hills but not on the flats. I checked my mileage from the display and had calculated and it was within a tenth or two.

[2oldman]

did you forget you already posted this?

[73guna]

I'm well aware of that. I varied my speed and check the mileage even when there was no wind. It never changed.
6.5 miles per gallon I would expect going 80 miles an hour up and down the hills.
I think there's more to it than just slowing down.

[MudChucker]

Cruise burns fuel... Lots of it.

[donn0128]

Slow down! Fuel economy is greatly effected by load, speed, and head wind. Were, or are you looking at the lie o meter or hand calculating? Also guessing weights is plane crazy. Stop at a set of scales and get real weight numbers.