M.D.S. - What is it? & How do I know when it is active? - Jeep Commander Forums: Jeep Commander Forum
Electronics / NAV Discussion This section contains discussion about the electronics system and NAV system in the Jeep Commander.

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post #1 of 61 (permalink) Old 10-06-2009, 06:34 AM Thread Starter
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M.D.S. - What is it? & How do I know when it is active?

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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post #2 of 61 (permalink) Old 10-06-2009, 11:41 AM
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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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post #3 of 61 (permalink) Old 10-06-2009, 10:34 PM Thread Starter
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Thanks. Makes sense.

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post #4 of 61 (permalink) Old 10-06-2009, 11:12 PM
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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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post #5 of 61 (permalink) Old 10-19-2009, 05:25 PM
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Does the 06 HEMI have MDS?
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post #6 of 61 (permalink) Old 10-19-2009, 05:35 PM
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Quote:
Originally Posted by Rush View Post
Does the 06 HEMI have MDS?
Yes.
......

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post #7 of 61 (permalink) Old 01-17-2010, 08:52 AM
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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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post #8 of 61 (permalink) Old 01-17-2010, 09:21 AM
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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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post #9 of 61 (permalink) Old 01-17-2010, 09:24 AM
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I found another thread that deals with MDS: https://www.jeepcommander.com/forums/...ad.php?t=10433

Nice explaination, Robby.

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post #10 of 61 (permalink) Old 01-17-2010, 11:45 AM
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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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