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What's the operating range of the MDS in the '09 and '10 5.7 V8, ie the vehicle speed? Also, what is the impact of the MDS on avg fuel economy shown on the trip computer during level cruising? I thought the MDS kicks in from 40-60mph and had a significant increase in fuel economy. However, my brother in law said it works up to 75mph on his Challenger R/T and the mpg increases by 2mpg to a spot average of 25mpg when cruising on the highway at 70mph. A 2mpg increase when MDS kicks in seems low considering that half the cylinders aren't in use.
 

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The MDS operates till a predetermined load is exceeded.
This will be a somewhat lower speed in the Jeep primarily due to wind resistance.
Although at first thought one would expect a larger difference in mileage, you must take into account pumping losses.
Even though four of the eight cylinders are shut down, all eight pistons, all of the bearings, the camshaft, all accessory drives are still siphoning power.
At the moment MDS kicks in, the ECM opens the throttle to compensate for the increased work the remaining four cylinders are asked to do.
At that moment, the injector pulse width becomes just short of double, and that little bit of difference is what is seen as a mileage increase.
Since the EPA mileage standards are measured in tenths of a MPG this 2MPG increase is beneficial towards increasing the corporate average reported fuel economy.
So, considering nothing has changed except for four cylinders doing no work and four cylinders being asked to do the work of eight, with the aforementioned pumping losses....two MPG is pretty good.

Rob
 

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The MDS is programmed to activate between a certain interval of speeds. Beginning with the 2009 models (maybe 2008s also ?) the speed range the MDS operates in was increased. Also, beginning with the 2008 MY an MDS on indicator was put in the instrument cluster.
 

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How do I know when the Hemi switches to 4cyl mode? 09 model

The reason I ask is, there is no way to tell and my mileage is well below the average. I'm only getting around 16 on the highway at 70mph (12 in town). I took the Jeep in for its first oil change on Friday and had a discussion with the service manager about this. He said that they added a light on the 2k10's to let the driver know when the MDS is activated (eco-mode). My 09 does not have this and I'm not too sure its even working. I realize that my mileage will get better as the motor breaks in but I hoped to get a little better than what I am getting right now.
 

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I am under the impression the MDS will not operate above around 65 mph.
The wind drag is too high over that speed and all 8 cyls are needed.
At least, that seems to be the general thinking.

If you have the radio off, fairly quiet road, you may hear a exaust tone change at steady throttle.
The ones I've ridden in seemed to do it around 50/55 mph.....accelerating gently to float at that speed.
That tone change is occuring because the engine went into 4 cyl mode.....changes the exaust pulse.

Rob

BTW, 16 isn't too bad for a fresh driveline and you are in a hilly part of the country, aren't you?
If so, that will kinda conspire against mileage too and thats when the weight of the vehicle comes into play on the uphills.
Just a additional thought.
 

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Thanks for the explanation, that was much better than the SM gave me at the dealer on Friday. I drive 7 miles to work everyday (14 round trip) at 4:30am and I usually set the cruise at 50 (in a 45 zone) and rarely get stopped by lights as there is little traffic. The trip home at 4:30pm is a different story, LOL! Its all stop and go in the pm.

I live in the Blue Ridge Mtns and it is steep terrain, (up and down/KYA curves) driving and few flat/straight spots of more than a 1/2 mile or so.

Does the MDS work when coasting?

Should I have a light in my cluster for when it is operating? (09 Hemi Limited)

If so, then its not working, no lights have ever come on. Is it possible that the MDS has been disabled?

Should I take it to the dealer to see what the issue is?
 

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The reason I ask is, there is no way to tell and my mileage is well below the average. I'm only getting around 16 on the highway at 70mph (12 in town). I took the Jeep in for its first oil change on Friday and had a discussion with the service manager about this. He said that they added a light on the 2k10's to let the driver know when the MDS is activated (eco-mode). My 09 does not have this and I'm not too sure its even working. I realize that my mileage will get better as the motor breaks in but I hoped to get a little better than what I am getting right now.
The light was added beginning with the 2008 model.
 

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Like I said, 5253 will show up.

5253?
Do you know where this MDS light is located?

Rob
Not specifically, but it is in the instrument cluster. Maybe some one who has it could post a pic of it.
 

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Manual says ECO is displayed on the compass/temperature page.
When ECO is displayed, MDS is active.
The feature can be turned on/off.
Press and release the function switch till ON or OFF appears.

Rob

This is out of the owners manual.
That is why I have not seen it, I keep mine on the "average economy screen". I looked through the owners manual but did not find it.

Thanks for the help!
 

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Ok, so I went for a drive on I-581, 18 miles round trip on the flattest interstate around here. I had the screen on the "compass and temperature" view and drove with the cruise set at 55mph.

Still no "eco light". Even on long down hill sections of the road, no eco light!

I do not think this feature is working on my XK.
 

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Ok, so I went for a drive on I-581, 18 miles round trip on the flattest interstate around here. I had the screen on the "compass and temperature" view and drove with the cruise set at 55mph.

Still no "eco light". Even on long down hill sections of the road, no eco light!

I do not think this feature is working on my XK.
Did you go into the menu and set it to display when it is on ? See Robby's post #17.
 
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