Installed my MDS light last week. It really helps you keep the hemi running on 4 cylinders if you try hard enough. Pretty much have to stay within the speed limit to do this. Many people are not happy with MDS, I am very happy I have the option to get decent gas mileage with such a powerful truck. Took a trip from Hartford, CT to Killington, VT - about a 155 miles each way.

14.4 MPG's on the way up, against the wind averaging about 73 mph on highway, 1/4 of the drive with cruise control. This would be my normal driving conditions

21 MPG's on the way back, staying within the speed limit. Probably averaged around 60mph on the highway to keep MDS active for 90% of the time. What I've learned so far is that MDS works much better on those 50mph rural route roads in VT.

 

BHS, i just bought an 09 cc trx with mds. i really can't find any info on how it works. i have only put 2000 miles on her but not any highway miles. how will i know if i am operating on 4 cylinders?

trouttamer
fishns great in ny upstate

 

I'm not real sure on the 09. But this was not a oem light in 06 so I had to follow some DIY instructions. Link below.

http://www.*********.com/forums/showthread.php?t=180371

swap *'s with *********

 

thanks for the link BHS

 

Well, the difference between 73mph and 65mph is like 2-3mpg, so it's not ALL the MDS that gave you better mileage, but more so that you slowed down, plus you went against the wind and UP hill.
Not saying mds doesn't give better mileage, BUT you do have to stay within thr 40-50mph range to benefit from it.
Apples -Apples at 70mph on the highway, mds doesn't help much at all. Maybe like 1mpg if that, not to mention your truck is constantly kicking in/out of mds non-stop at that speed. Mine could not stay engaged above 65mph without the truck slowing down, then kicking out of mds and sometimes even downshifting to pick back up speed just to go through the same routine all over again. ANY slight incline on the highway and it gave the mds trouble. Think about it, we have a huge wall runing on 4cyl. Doesn't go through air all that well.
Okay, gonna stomp all over mds now that I have you warmed up. The shifting schedule flat out sucks. i know, your prob thinking your truck shifts great. I kinda did to. Then I bought a programmer. Right away with mds disabled the truck had much more response and alot less delay to downshift and pass. It was like I was driving a new truck. Couldn't believe it. The trucks should shift like that from the factory.
if you drive like an old man...MDS is your friend
If not, disable it and you'd be much happier. I'm 16/17mpg going 70mph on the highway on average with mds disabled using the tuner. Still better than most other truck out there with comparable power.

 

DirtyDog, that is good info thanks. The only difference I have is the ability to the light that I installed. After you watch the light for a while you can watch it to make sure MDS is not going on and off. I kept the light on for more than 90% of my trip. I would tend to agree that if I had it disabled at this same speed my mpg may only suffer 2mpg or so. Again, its nice to have the option!

I would like to have a tuner eventually. I hope it would be easy to enable MDS easily with it though.

 

You can have a handheld programmer(tuner) and still keep MDS active. You can even still alter the shift patterns and keep MDS....FYI
Maybe it's something to look into, because the stock shifts are kinda bad IMO. raising the rpms where the truck shifts at results in better everything including mpg's. And it prob helps keep MDS off until your up to speed rather than kicking in super early which results in lagged performance.

 

I installed the MDS light last week. It is interesting to see how and when it comes on and goes off. It seems to be on a timer of some sort, because it won't come on right away. At first, I thought it was related to engine temp, but it appears more like time-based. It also goes off between 900-950 RPMs. So when coming to a stop, it turns off after 1k RPMs. I have only driven about half a tank since installing the light, but with all of the snow and 4x4 (which btw, the truck in 4x4 w/ the Coopers has done great), it's not my normal driving style/pattern. I found that on my normal city commute, I can actually keep it in MDS quite a bit, since the speed limits are 40. The question is will it help my mileage. I've been averaging about 13.5 mpg.

I figured I may as well install the light just to see how it's doing. I do hope to get a programmer and exhaust at some point. Really, the MDS is the main reason I haven't done exhaust yet, and I don't want to pay for a programmer either.

Oh well.... spring will be here at some point, then I go back to my motorcycle which gets better mileage, is faster, and has better exhaust!

joe

 

65mph on Flat ground with MDS on after 50 miles =

 

LinerJoe, Great info. I have been trying to figure out the MDS patterns, the timing and rpms do make sense. I really wish the light would stay on for lower RPMS, for traffic or stop lights.

Lxman1 - thanks for the stats. That is impressive..

Please continue to post any other MDS/MPG related stuff.