Truck is a CC with 5.7 and 3.55 rear.
It seems I'm one of the few that doesn't notice the MDS kick in. I have an early build so no light.
I also seem to get terrible gas mileage anywhere from 11.5-12.5mpg. I do mostly city driving with a little highway mixed in. Probably 80/20-city/highway. The truck is stock and I don't drive it hard at all. I"ve tried 87 and 89 octane with no difference. I had a Mufflex DOD14 system on and got an increase of about a 1/2mpg.

On a long trip of about an hour on the highway it creeps up around 14.5mpg.

I've hand calculated and it's pretty close to the computer.
These numbers seem to be alot lower than what most are experiencing.

Anyone have any ideas as to why the mileage is so poor? Could the MDS TSB flash help or hurt? Like I said, even with the Mufflex I cannot tell when the MDS kicks in.

 

i too have an really early 09 build. i cant really tell either when it kicks in. unlike my 08 grand cherokee overland. you could tell even without the light.

i have a 4x4 sport quad cab w 3.55 gears. in MI. its been hovering around 30deg. lately i seem to be getting about 13 city. 16 highway.

but in the summer i would avg. about what the sticker said, or more.

mostly 15city 18-19highway. doing 70mph....

 

In order for me to get to 14.5 on the highway I have to keep it under 65mph. Any faster and the mpg drops.

I would think with the cooler themps gas mileage would improve a touch if anything??

 

Are you resetting it when you get onto the highway? The computer doesn't say the mpg's you're getting at that exact moment, it's gives you an average from the last time it was reset.

 

I never notice it either, I personally don't think I even have it I have tried to watch the revs increase that tiny bit after going like 40 with cruise on, nothing, dealer says it works, I asked how they know they can tell they said.BS.

 

I don't re-set it. I understand it gives the average. I didn't realize people were actually re-setting it to get the numbers they do.

 

Even if your not resetting it.... if it starts dropping below 14.5 keeping it above 65 then its abnormal

 

Just remember everything else is cold too and need to warm up. Tranny fluid, rear end transfer case etc.. Lots of drag there..

 

scotty. does your truck have the 3.55 or optional 3.92lsd? that makes a huge diff...

 

I have the 3.55's.