Upgraded 9 to 13 speed, MPG takes a dump

In advance, thanks for the help and also, I know who I work for and if you just have a snide comment, please, just move on. Okay, now on to the problem. About 3 weeks ago upgraded my eaton from the 9 to the 13 speed. It already had the conversion kit installed so just added the two air lines and knob. Prior to that I was averaging in the mid to high 8's on fuel. After it has taken a dump. Example, load from PHX to Fort Stockton, 6k in the box, mpg 7.5 and a tailwind. Now I have replaced the fuel filters, air filter and have already dumped 1 gallon of Howes to see if it helps. For the last 2 weeks, averaging around 6.5-6.9. I do not know what rears I have, (sorry). It is a cummins ISX.

Is there anything else that you can recommend. I did talk to a mechanic and he mentioned that when the conversion was done, if they did not go into the system and re-do the parameters, then it is like the conversion really did not happen. Oh, 2 weeks ago, the ECM was re-calibrated after Cummins finally found what was causing all of my DEF/DPF problems. Some are saying it is because of the cold weather. this is my 3rd winter in the truck, and never have I experienced mpg below 7

thanks again.

 

Thanks. I still drive it the same way, and in fact, I do not split the upper gears unless climbing or in stop and go traffic, 25mph to 45mph and back. If on level ground shift the same old way until I get to 60, then split to OD. It is running at 1400rpm for 65. What is getting me, I am hauling pretty much the same that I was last year in most of the same area, and getting almost 2mpg less. I now have 290k on the truck, and nothing has been done to it other than the conversion and re-calibrating the ECM. I think maybe I need to get it DYNO'd and see what is going on. I am going to also keep trying this Howes and see what happens. Thanks again for the help.

 

Thanks again. I was asking around regarding the treatment, and I was hearing Howes. In all my years of driving, never used a additive before. Just trying whatever comes to mind to get my mpg back up again. As far as idling, really do not do that much. I have the Espar in the truck. When I am upshifting I am shifting at 1600 as far as the low side and about 1400-1500 on the high side (5-6), (12-13).

 

Thanks Lucar. Did you notice the date of that test, 07 and actually Howes was not that bad, if I read correct. Products 16-19 where worse. Could not believe that I saw used oil on the list. Never would have thought that some one would use that. Like I said, in all my years, never used additive before. I kinda go with what Mechanics recommend, and not those from our shop.