I have a 2008 GMC Sierra 3500HD 6.6 turbo diesel that I have recently started to mysteriously lose mpg with. It is getting up there in miles (476,000) and I do a lot of RV hauling with it. Over the last month and a half I have noticed a random loss of 3-4 mpg. Before this, I was always getting 12-14 loaded and 19-21 unloaded highway driving. Now I am getting 9-11 loaded and 15-17 unloaded! I have not noticed any power loss and I put an EDGE on the vehicle and did a forced regen and all my injectors balance rates were normal. I have also used injector cleaner but it did not change anything.
However, ever since I have owned the truck I have had weird problems with my MAF sensor. Whenever it is damp out or cold when I first start the truck up I usually get a MAF sensor circuit control error and the truck is in reduced engine mode. I usually have to wait 10-15 minutes and then clear the code and it doesn't come back. When this first started happening I brought it into the dealership and they told me the sensor was fine and that I had a bad wire, and that they fixed it. About a month later I started getting the same results when I first started the truck up and it was cold or damp out. It has never affected my fuel economy though and I have just lived with it.
So my question is, now that I am experiencing this mpg loss, could it be my MAF sensor has finally gone bad? I should mention that I did try cleaning it when I first got the truck and that did not seem to change anything. Could it be something else causing this? What do you all think?
However, ever since I have owned the truck I have had weird problems with my MAF sensor. Whenever it is damp out or cold when I first start the truck up I usually get a MAF sensor circuit control error and the truck is in reduced engine mode. I usually have to wait 10-15 minutes and then clear the code and it doesn't come back. When this first started happening I brought it into the dealership and they told me the sensor was fine and that I had a bad wire, and that they fixed it. About a month later I started getting the same results when I first started the truck up and it was cold or damp out. It has never affected my fuel economy though and I have just lived with it.
So my question is, now that I am experiencing this mpg loss, could it be my MAF sensor has finally gone bad? I should mention that I did try cleaning it when I first got the truck and that did not seem to change anything. Could it be something else causing this? What do you all think?