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When the MDS Functions Per the Engineers

16K views 34 replies 21 participants last post by  roo 
#1 · (Edited)
Here's more from the Engineers.

MDS will function when the engine speed is between 1000 and 3000 rpm, and the engine is hot. Then whenever the torque required to move the vehicle is able to be met with 4 cylinders the engine will switch to MDS mode.
Edit: they added that in order to tell if MDS is on/kicked in the ECO light on the EVIC will show. Therefore, no need for any kind of MDS light.
 
#4 ·
Should be the same thing. Easiest way to know for sure is to look at the RPM and whether you're not accelerating but just maintaining speed.
 
#5 ·
Ahh soo much answered.. so the ECO light in the Evic IS on in mds mode. That's the only clue I have when MDS is on. I can't tell from sound or anything. I dont have the growl or groan as some say they hear when its on. I guess Im lucky to not hear it. I do notice when it is on it takes a little bit to kick back into all 8 when I have to do evasive maneuvers.

Good find Brian.
 
#6 ·
Here's more from the Engineers.



Edit: they added that in order to tell if MDS is on/kicked in the ECO light on the EVIC will show. Therefore, no need for any kind of MDS light.
There have been posts on this that say the ECO light does not always mean the the vehicle is running on 4 cylinders but that you are simply driving in a fuel efficient manner. :doh:

So am I to take this as the latest and official word that the ECO light means that the vehicle is only running 4 cylinders when it is on? :thk:
 
#7 ·
That's what the engineers said.
 
#9 · (Edited)
If you are driving in D not 5 it will appear at the top of the display centered in your dash above the steering column.

Its not on in this pic, but it would be between the NE and 85F. That is if you have a 1500 1/2 ton.

 
#11 ·
My truck must be a freak,,,, MDS will activate when engine has not yet reached norm op temp, as is 'on' @ 130 degrees. At low speeds I can hear it w/my magnaflow exhaust and verify w/data logging on my Cortex. (via MAP readout relative to throttle position)
Also, on my 09 w/Fuel Saver light,,, FS light USED to come on only with the MDS,,, Went in for the HVAC 'recall', dealer flashed the ECU, and the friggin FS light comes on all the time now, w or w/o the truck in MDS mode. (I drive very conservatively) Comes on so much it wasn't 'beneficial' so I simply disabled it in EVIC.
 
#12 ·
i have a 09 laramie and it never had the fuel saver light on it when i bought it. After reading some info on here i went to the dealer and they updated my ECU and added the fuel saver light. It appears in the bottom right corner on the dash. Also there is a setting to turn it off and on in your set up mode on the dash. yours may just be turned off. Go through the settings and have a look.
 
#15 ·
This came up on another post on the site, and I was under the impression that the MDS didn't come on until the engine was up to operating temp or at least a more reasonable temp. I found on my '12 Express that the MDS appears to come on at the first opportunity, and that's well before any reasonable operating temp has been achieved. Not sure how the earlier models read MDS engagement. I don't have EVIC, so the "ECO" symbol in my dash readout has an "ON" symbol when MDS kicks in. If I'm driving in a manner suited to the MDS coming on, it seems to always come on regardless of the temp. Regardless of the constantly changing "ON" light for MDS, I think one can easily tell when it comes on and off if you're in tune with how your vehicle responds. I don't find it annoying, but I can almost always tell when MDS is in operation...except perhaps some highway scenarios at speed where the MDS operation is pretty well seamless.
 
#16 ·
now that i have gotten an exhaust, i found that the "eco" in the display above the rearview mirror has nothing to do with the mds on my truck at least. eco is always displayed, never goes off and with the new exhaust i can def tell that the mds is working, i can clearly hear the switch.
 
#17 ·
now that i have gotten an exhaust, i found that the "eco" in the display above the rearview mirror has nothing to do with the mds on my truck at least. eco is always displayed, never goes off and with the new exhaust i can def tell that the mds is working, i can clearly hear the switch.
I'm not familiar with the rearview mirror MDS display. Does it mean that MDS is operating when the "ECO" is displayed, or is there an "ON" that is supposed to accompany the "ECO"? On my '12 in-dash display there is always an "ECO" display when you scroll to it. When MDS is engaged there is an "ON" that comes on to accompany the "ECO" symbol. Does your mirror display just have an "ECO" or is there also supposed to be an "ON" indicator...or something to indicate when MDS is operating and when it's not? It would seem odd to not have something giving an on-and-off indicator of the operation of MDS.
 
#19 ·
Ok so the conclusion is that there is no way to know if the MDS is active unless you have exhaust or are in tune with your motor? My 06' tells me nothing. I will look to see if it has an eco light when I get it back from service ha. But from what everyone is saying that has nothing to do with it anyhow. Not that it makes a huge difference if it has an indicator or not "but" it would be nice to know when it is working. I used to own a Durango with the old 5.7 HEMI without MDS so it will be interesting to see what I can get for milage with the new motor. Just got the RAM 3 weeks ago.
 
#20 ·
Ok so the conclusion is that there is no way to know if the MDS is active unless you have exhaust or are in tune with your motor? My 06' tells me nothing. I will look to see if it has an eco light when I get it back from service ha. But from what everyone is saying that has nothing to do with it anyhow. Not that it makes a huge difference if it has an indicator or not "but" it would be nice to know when it is working. I used to own a Durango with the old 5.7 HEMI without MDS so it will be interesting to see what I can get for milage with the new motor. Just got the RAM 3 weeks ago.
That's interesting. I see that '06 is the first year for hemi MDS in the Ram. Maybe another '06 owner can chime in with how the MDS engagement is supposed to be displayed in a readout.
 
#21 · (Edited)
These are the pages found in my 2012 manual. IF you have the EVIC it says one thing and actually addresses the MDS, otherwise it only addresses ECO ON/OFF. Since I do not have the EVIC I dont know if my truck is set up to use the MDS function, it does show the ECO ON/OFF but according to the manual that fuel economy based. I do know that the other day I was traveling I-10 east to Houston TX and as long as I was on flat road & in cruise control the ECO ON showed. As soon as I started up any incline, it switched and the ON disappeared. It did the same even if I was not using cruise control. The transmission did not downshift, and the RPM's only minimally decreased.

 
#22 ·
EVIC or not, you have the same functioning MDS on your model truck. When the display that has the "ECO" symbol is scrolled to, the "ON" symbol means your MDS is engage...4-cylinder mode. The reference to "Fuel Economy" in the EVIC display is just the same thing for a different display method. You have MDS. Most people can hear or feel the MDS kick in and out, though I'd agree that it's a bit harder at highway speeds. Yes, it goes off fairly easily on slight grades or even moderate head winds.
 
#25 ·
When MDS comes on in my 09 I can hear and feel it switch over..at the same time the fuel saving light comes on..every time..doesnt matter the temps..even at -35 and with a cold motor it will come on. One thing I dont notice is the fuel usage meter changing when it switches..technically it should drop from 18mpg in 8cyl mode to 14mpg? in MDS?
 
#28 ·
MDS will come on when engine senses no need for 8 cyl, no matter how cold according to the service rep at my dealership. But, if your driving with the MDS 4cyl mode engaged in cold weather and engine gets too cool for the ECU's liking, it will turn off the MDS system firing all 8cyl to warm up the engine. Both ways are for better fuel mileage also from the rep. It makes sense if you think about it, less fuel used in "cold choke" mode and the ECU also keeps engine at 203° for better MPG driving down the road.
 
#29 ·
MDS will come on when engine senses no need for 8 cyl, no matter how cold according to the service rep at my dealership. But, if your driving with the MDS 4cyl mode engaged in cold weather and engine gets too cool for the ECU's liking, it will turn off the MDS system firing all 8cyl to warm up the engine. Both ways are for better fuel mileage also from the rep. It makes sense if you think about it, less fuel used in "cold choke" mode and the ECU also keeps engine at 203° for better MPG driving down the road.
I don't know. That looks like a contradiction to me.
 
#30 ·
Well it does if you look at it from "their MPG/Emissions" viewpoint. Four cylinders dumping gas in a cold engine is better than eight dumping gas, less fuel better MPG and less emissions. When the engine gets up to temp, ECU's 203° setting, and four cylinders can't keep the engine heat up for the 203° setting, off goes the MDS so the eight cylinders can heat coolant back to 203°. The 2013 RAMS have the grill with shutters to cut down on air to radiator, which helps aero drag and too much cooling for ECU's liking.
 
#32 ·
I asked that question specifically since the MDS will come on less than 2 blocks from my house with a dead cold engine. Always has. The service rep said the MDS operates on its own settings. Mine does exactly what he is saying it should. :4-dontknow:
 
#33 ·
Ok I've had my ram for a few days only and it's obvious when it's on, the exhaust note/vibration doubles in speed and if u push down more on throttle it goes away. No need for a light it's clear as day. Unless my trucks messed up and that's not how it feels lmao
 
#34 ·
17° Sunday morning, shifter in D, MDS comes on 2 blocks from house, as usual. I'm positive the ECU controls the MDS on/off parameters for engine management.
 
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