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"Multi Displacement System (MDS)" or cylinder deactivation turns off the fuel in four cylinders when power is not needed.
This system triumphs because of modern electronic controls and electronic throttle control. The HEMI can transition from eight cylinders to four in 0.04 seconds. The system works by cutting out the valve lifters, keeping the valves in four cylinders closed; energy is not lost by pumping air through them.

Info was gathered from allpar.com Hope this helps!
 

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When I am cruising along, the engine changes pitch, sounds like it is dropping out of overdrive, and then going back into overdrive. Or perhaps the MDS is kicking all eight cylindersw in and dropping them out again. Any ideas or suggestions would be appreciated.
 

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Actually, you can temporarily defeat MDS... well documented on this site.

Just flick your transmission into '5', and the MDS will stop. I usually keep mine off while beginning my drive, and when on residential streets.

However, as soon as you shift into any other gear, that resets it back to 'on'.

Darin
 

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I've only been on this forum for about 3 months with a new Ram truck, but I notice one issue fairly frequently. It seems a lot of folks don't read many, maybe any, of the currently running posts about our trucks. No, I'm not a search nazi, but when the answer to many questions is only 5-10 posts down on the same page, it makes you wonder if some have read any of the posts on this site. I do not mean to sound disrespectful, because I'm not. I just hate that people who are looking for info might be missing some well researched and valuable comments that have already been given...over and over...on the same page they're asking the question on.
 

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thats' just part of an open forum, expect to see retorical questions. As a user you can reply, or hit the back button.
 

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thats' just part of an open forum, expect to see retorical questions. As a user you can reply, or hit the back button.
Yes, I know what you mean. I'm not new to other enthusiast forums, but maybe that's the difference. Dirt motor, mountainbike, and other specific activity sites are probably more focused and inhabited by a narrower user group. I've never spent this much time on a mainstream vehicle forum before, and it seemed odd that quite a few posters weren't reading much of the info previously covered in recent posts. I guess it's like opening up a service manual, getting the info you need, and putting the manual back up...LOL! And don't get me wrong...it wasn't like I was upset or such...just surprised. But being such a mainstream vehicle, it makes sense upon reflection. Still, this truck is so cool to me compared to many of the other automotive vehicles that I've owned, it's almost like a hot rod, sports car, or other enthusiast vehicle...LOL!:D
 

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OK, good to know there's a way to defeat it (I was wrong) - is that in the owners manual too (I don't remember seeing it)?

Guys - you can't really blame people for not being familiar with every thread ever posted on an internet forum. You know, there's like 1000 new threads per day on this site. I don't have the time to read every one.

I will have to test this theory about improved throttle response while MDS is off. So just kick it into "5" as in 5th gear? I don't play with the gear selection much, but it doesn't seem like a great idea to have it in 5th unless at highway speeds?
 

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Yes, kicking it into "5" will disable it. That is the only way I drive my truck now. Absolutely no difference in gas mileage but all of my driving is in town anyway so it would be hard to tell. What I do notice is that truck seems more responsive when I need to get on the throttle a little.
 

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OK, good to know there's a way to defeat it (I was wrong) - is that in the owners manual too (I don't remember seeing it)?

Guys - you can't really blame people for not being familiar with every thread ever posted on an internet forum. You know, there's like 1000 new threads per day on this site. I don't have the time to read every one.

I will have to test this theory about improved throttle response while MDS is off. So just kick it into "5" as in 5th gear? I don't play with the gear selection much, but it doesn't seem like a great idea to have it in 5th unless at highway speeds?
diligent, that's a good question as to why it's not in the owner's manual. The reason is probably based on the fact that the fuel economy numbers earned by the given truck/engine combination are a result of running on the MDS. If the manufacturer promotes or suggests that you can easily turn off the MDS, they might run afoul of the EPA or some other element of the fed concerning the fuel economy numbers and CAFE standards. At least that's my speculation.

You are not going to hurt the engine or tranny by disabling MDS if it really annoys you. It just means you are running on all 8 cylinders all the time instead of going into the 4-cylinder mode at certain times. The only "hurt" might be fuel economy to some degree.
 

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OK forgive my ignorence but is that not putting the auto transmission in it's highest gearing all the time? I don't fully understand autos and TC's, but that would seem to me the TC would have to do all the work (in the viscous coupling) if the tranny is always 5th gear.
 

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OK forgive my ignorence but is that not putting the auto transmission in it's highest gearing all the time? I don't fully understand autos and TC's, but that would seem to me the TC would have to do all the work (in the viscous coupling) if the tranny is always 5th gear.
First off, in our trucks, the manual gear selection only "limits" the transmission to the highest gear selected. It doesn't actually force that gear like some "manumatics". So, if you select 4, you'll still use 1,2, and 3 as well.

Second, before 2012, we have what's classified as a 5-speed, but actually have 6 gears. Essentially, there's two different gears used as 2nd when in fully-auto mode (2 and 2P), a lower one used while starting and progressing up through the gears, and a higher one for kickdown. For 2012, the transmission is essentially the same box, with the same ratios, but has been reprogrammed to use all 6 gears.

When you manually select a gear, the numbers that show in the little window on your EVIC include 2P. So, 1(showing)=1(actual), 2=2, 3=2P, 4=3, 5=4. For driving around town, selecting 4(actually 3rd) or 5(actually 4th) is fine, but the only way you can get into your top overdive gear (6) is in full auto (with MDS enabled).

I find it hard to believe that anyone would get even the same MPG on the highway leaving a gear on the table and not taking the fuel savings of only running 4 cyls when you can.
 

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Actually, you can temporarily defeat MDS... well documented on this site.

Just flick your transmission into '5', and the MDS will stop. I usually keep mine off while beginning my drive, and when on residential streets.

However, as soon as you shift into any other gear, that resets it back to 'on'.

Darin
That's interesting-you just answered some thoughts of mine.
 
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