I am new to the Duramax, i have a new LMM, when i first got it it was geting about 14.3 mpg when i hit 11000 miles it was about 15.5 mpg. my question is i just put a new MBRP turbo back exhaust on because ive been reading about the better mpg everyones been geting. now im alil over 12000 miles, sense the new exhaust my mpg went down, now im at 14.6 i dont know why, love the sound but hate the mpg.
Can anyone help THANKS.

Welcome to the Might Max......I'm not sure but with all of my prior diesels...mileage always went down at first....at least until I learned to control my ear-to-right foot issues...:D

Seriously though....have you been driving it exactly the same? I've always seemed to get "on-it" a little bit more on take off with exhaust mods and my mileage suffered until I made myself stop.

yes ive tryed that, i even tryed driving slower then normal for a few dayes. nothing seems to work its just stuck on 14.6. its been like this for 2 months. i dont know whats wrong.

I've also experienced better fuel mileage...by an average of up to 2 mpg...at one truckstop versus another. Have you changed where you normally were getting your fuel at?

Sounds weird...I know...but I have a Crazy D's that's only 4 miles from my house....and I get my fuel at a Love's that's in the town where I work....which is 15 miles away.

I averaged this for months at a time to take into consideration that maybe there was some "not-so-good" fuel in just one delivery. I also accounted for winter fuel and did the comparison in the summer months too.

I ended up always getting 2 mpg better at the Love's. My truck also runs considerably better on the one fuel versus the other. My mpg's were hand calculated too...by the way.

yes ive tryed every place around were i live. but i dont think it was that. the day i put my new exhaust i was geting 15.5 and and right after i put the exhaust on i was geting 14.6

Where are you located? If you're up N, then you're using #1 and the mpg's will suffer some through the 'winter' months. Also, are you running any additives? If not, you should seriously consider that. It would help if you fill out your sig, so that we have more info to assist you, joe. Hope this helps!

I live in Maryland and it hasent been that cold. its been right around 40o - 50o. what kind of additives should i us im new to diesel and im not sure. THANKS.

Thx Joe, ok, for starters, I would start by reading this excellent thread (http://www.dieselplace.com/forum/showthread.php?t=177728). Secondly, where you're filling up, do you know whether they're pumping 'winter blend'? Sometimes you'll see #1 listed on the tank. I also notice that you're running 33's on 20's; have you recalibrated your computer to make up for the difference? Lastly, do you hand calculate or rely on the DIC for mpg's? Without the recalibration and if you're not hand calculating, it's really not accurate to base your mpg info on this.

No i havent recalibrated for the bigger tires and i understant that makes a difference. But what i am saying is the day i put my new exhaust on is the day i started haveing this problem. i went from 15.5 mpg to 14.6 mpg. Right after i installed it. i think its somthing to do with the exhaust.

Dose anyone know anything else i can try

welcome to a fuel caled winter blend your milage should go up after winter when they switch back to regular fuel in the mean time theres really nothing you can do about it sorry

how long ago did u install it? It's possible and a strange coincidence but that could b the day they switched to winter blend.

it is not the exhaust. Or you are one of the 1st that had milage drop that I have heard of. An exhaust makes the "air pump" pump more efficent by less restrictions. When I put in my muffler delete I lost 1MPG because I was listening to it.

i understant what everyone is saying, and thanks for the help. but i keep reading how everyone is geting 19-20 mpg. im only geting 14.6 thats a big difference. thats what i dont understand. i dont drive it hard i try not to take it over 2000 rpm. no matter what i do it never changes form 14.6 its been stuck like that for 2 months.

I average about 15 to 16 MPG. Driving with occasional lead foot. I would have to disagree with you about everyone is getting 19-20 read some fuel economy threads I would say the average is about 16-18 for most.

Plus you have 07.5 according to the sig your motor probably is not broke in fully yet.

Again, Joe, how do you really KNOW what you're actually getting with the tire/wheel pkg you have on and you haven't recalibrated or seem to have factored in, which you need to do...........?????

Dose anyone know anything else i can try

The logical thing for me to do this situation is to simply bolt the stock exhaust back onto the truck and run the next month or two like that. Make sure you don't change other factors like tire pressure, driving habits, or feuling locations. Shouldn't take you long to find out if that exhaust is hurting or helping you...