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.

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.

Cruise burns fuel... Lots of it.

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.

did you forget you already posted this?

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.

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

LowRyter
Explorer
Aug 25, 2016
I tow at 65 or under. You might know that most trailer tires are rated at 65. But I stay at 65 or under for the fuel mileage, not for the tires. I usually set my cruise 5 under the limit or 5 under the prevailing traffic and never over 65 when trailering. I am not surprised with that mileage considering the weight and speeds. I'd fix the EGR too.
73guna
Explorer
Aug 21, 2016
Just got back from a 2300 mile family camping trip.
The final mpg was 9.7mpg. Prior to leaving our last camp site it was near 10.5mpg, the last 7 hr trip home I pushed the old Duramax so I lost some mpg overall.

I factored in my tire size diameter and came up with an overall mpg of 10.45. Im running 285/70/17 as opposed to the factory 245/75/16, so there is a couple inches in height difference.

The only thing I did different from the last trip was I cleaned the MAF sensor and removed the truck topper.
I cleared the egr code also and it never came back on during this trip.
I belive the MAF sensor may have been the issue.

Pretty happy with the mpgs and my setup weighed in at just under 18K.
mkirsch
Nomad II
Aug 03, 2016
Earlier you said that you "know your truck" or something like that, but back in the first post you said it was your "first trip."

So which is it? Is the truck new to you, or not?

If you've had the truck for a while, you certainly have an idea of the fuel economy it gets unloaded. How does the truck do unloaded? Was there a sudden drop in fuel economy unloaded?

A drop in fuel economy towing should also reflect in a drop in fuel economy unloaded. Maybe not as drastic, but you should have noticed it if you "know your truck" as you say.
JoeTampa
Explorer
Aug 03, 2016
AUwing2 wrote:
You might have the dealer look for a leaky injector or low pressure. I've had 2 DMax's, an LBZ and LMM. Both are consistent 10.5 - 11.5 with the occasional 12 when on cruise @ 62/63 mph. First tho, if it's running and starting fine, rerun your test at slower speeds and don't worry about getting up to full speed to fast.

I get 12 on average depending on speed and how flat the road is. I've gotten as high as 14 and as low as 10.
97chevor
Explorer
Aug 02, 2016
I suggest OP try driving 62 mph and see if milage improves.
allen8106
Explorer
Aug 02, 2016
2013 GMC 2500HD, long bed, regular cab, 4X4, 6.6L Diesel, purchased new.
2010 Jayco 31.5 RLDS, weighed 10,500 at grain truck scale a year ago coming home from the lake.

13,279 miles mostly towing - 11.48 mpg (75% or more towing)
5,241 miles some towing - 14.85 mpg (less than 25% towing)
40,428 miles no towing - 17.0 mpg

These numbers are based on actual numbers from 132 tanks of fuel between 10/19/13 and 7/23/16.
Jpatrickc
Explorer
Aug 01, 2016
My 2006 LBZ gets 10-11 MPG pulling a 15,400 lb. fifth wheel. The 2 things that make the mileage change for me is speed (I usually run about 64-65 mph) and mountains.
I just did a trip with the truck alone with about 1000 Lb. in the bed and got 17+ mpg.

Pat
73guna
Explorer
Jul 30, 2016
kw/00 wrote:
Sorry hearing about the damage to the house and camper. Yes these threads eventually turn into a p....sing matchs and get locked. So you mentioned a tune. I suggest Black bear performance, they are big into GM trucks. Your truck should get better not sure why, but you could need a dpf cleaning cause they all get clogged eventually and need cleaned or replaced. We have this issue at work with our Ford trucks, so the Dpf system filter get replaced or professional cleaning. Anyway keep us updated if this thread survives....

Thanks kw, I appreciate it. And your second sentence couldnt be more right. You seem to get it, I wish others would :)
Hopefully my thread wont get deleted, but just slowly fade away so I can report back when I get the problem solved.

Im lucky, no dpf on my truck, that came out in 2007.5.

I'll keep you all updated.
goducks10
Explorer
Jul 29, 2016
Grit dog wrote:
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?

No, he's related to a guy on the cummins forum who gets 27mpg highway with his def deleted 4th gen with the AC off and 18mpg pulling his toyhaulers. Amazing how a few people are able to defy the laws of physics with these trucks. Wish I had one!
But I'm happy with 10-12mog loaded and 18 unloaded.

Some of my best mpg's has been cruising the net. I always get 3-5 more mpg on the net.
Searching_Ut
Explorer
Jul 29, 2016
There must be something really wrong with your truck. My Ram gets 30mpg towing my 5er if I slow down to 80mph or so.....

Now that I think about it, maybe it was around 10mpg at 65, I get a little confused sometimes. That said, was your decreased mileage during the heatwave? Things I've noticed over the years that have a significant impact on fuel mileage are the normal speed, weight, wind etc. I've also noticed that fuel blend and temperature can make a noticeable impact. Towing at 90 to 100 plus degrees tends to have a significant negative impact on my truck.