If a Duramax owner, whose truck is under warranty, believes that the vehicle is failing to give the fuel mileage it should, might be able to get the dealer to connect an analyzer to the computer. The truck must be driven while connected to the analyzer. We had our Duramax tested with a five ton trailer in tow on a six percent grade on I-17 in Arizona. According to the analyzer, we now have 97 per cent efficiency, which gave us between 13-14 miles(average)per gallon on continuous hills and grades on the interstate southward from Flagstaff. Non-towing on I-10 between Phoenix and Tucson yielded 18.6 on Monday. Trying to find a dealer who was willing to do this test was not easy. It takes a technician away from the shop for a couple of hours. Since our truck is under warranty, there was no cost to us.















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That mileage seems a little high for a 10K pound trailer on hills and grades.


Are other getting that kind of mileage pulling a trailer on continuous hills and grades? (I am not)


The non-towing mileage seems about right.Edited by: OC_DMAX

Seems high to me as well. I have the same weight trailer and the best I have been able to get, driving 60 mph is about 11 mpg.

The best I have done is 12mpg towing our 10k 5er on flat ground...in the mountains of Colorado, I can't get much higher than 10. Pulling Wolf Creek Pass (7% grade that never seems to end) my instant was showing between 3 and 5 mpg!! What kind of analyzer is this, Tech II, or something else??

We had the truck tested because we were losing power on the long grades in Arizona. On the Copper Canyon grade(I-17 at Camp Verde, AZ) I did not think we would make it to the tope of the hill. We had the same experience east of San Diego and also on the grade at Hoover Dam on the Arizona side. Hence, I began to agitate the dealership and was able to get the truck tested after several weeks of complaining. I had not expected an increase in fuel mileage, but mileage is greater after the work was completed, both towing and non-towing. The truck runs smoother and has greater acceleration than before. As far as the analyzier is concerned, I do not know the type. It was the size of a checkerboard and about one inch in thickness.

What did the dealer do to make it run better than before? New injectors, re-flash on the ecm? I wonder if you had a dirty fuel filter.

I sounds like you had a problem with the truck. I have never experienced a situation where the truck would almost never make it over a hill. Once the Allision shifts to 4th gear, there has alway been plenty of power for any hill that I have encountered (and we have some long grades in CA, similar to what are in AZ). Hope everything is working out for you now.


FYI - My mileage towing a travel trailer plus motorcylces/gear (total load 7K pounds) has consistently been 11-13 mpg (measured after each trip). The variation is mainly due to the winds and the number of mountain passes that are encountered on the trip.


My around town mileage has consistently been 15 mpg.


My "on-highway" @ 70-75mph mileage has consistently been 18-19 mpg. I have never hit that magical 20mpg number yet, maybe some day.Edited by: OC_DMAX

The dealer did not change the fuel filter nor install new injectors. However the truck was at the dealer for most of the day. The computer may have been reflashed but I cannot say for sure. The technican made several changes on the analyzer while the truck was under load. I wish I could be specific.

Milage for me is 18 .5 no load staying below 65. I get 10 to 11 towing a 8000 lb. travel trailer. The difference in towing milage could be wind drag. A tall load of 10K will give less mileage than a low load of 10K that doesn't catch much wind drag.

They didn't put a box under the hood with EDGE on it did they?


Seriously,I can't get 10mpg with my 10000lb 5er on flat ground,that's great. Edited by: Bullseye54

Fisherman, I live in Gilbert and pull a 14000+ all steel gooseneck with living quarters to Flagg many times a year (sometime on 17 and sometimes thru Strawberry) and since the Juice was added I get 9 mpg doing the speed limit or more. Last weekend on a trip to TX thru Tucson, the lowest I got was 16.8 and the best was 19.8, doing 75-85mph the whole trip (even with the rain/juice issue, that is about to be resolved!). It looks like you got yours tuned in by a good dealer/technician. Enjoy the ride, I do!


BTW, was the dealer in Flagg? or down in the valley?


Mitch

The truck was purchased at a Valley dealership, but GM sent me to the Cottonwood dealership for testing. I can not say for sure but this dealership seems to perform a great deal of repair for Duramax owners whose trucks are performing below specifications.