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Discussion Starter #1
I am wondering if there is a way to tell when the MDS kicks in. I have a 2009 Ram Laramie and it has a Fuel saver light that comes on when you are light on the throttle but was told that has nothing to do with the MDS. The Fuel Saver light comes on even when its cold and i was told the MDS only comes on when the truck is up to operating temp. So i believe the fact that that light just means you are driving efficiently but not linked to the MDS. So my big question is how do i know if my MDS works or not?
 

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ive heard you can feel it when it kicks in (or out), however i cant feel when its on or off. So bump for ya!
 

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their is normally a way to turn the fuel saver light in the evic when you go in the programming mode, to go their start the truck, let it in park and if i remember right its the last option down to accest the setting,

after just go thrue all off them it should be call fuel saver light or something similar,
 

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There is no display to tell you MDS is active or not, it's all feel and sound. It is VERY easy to tell when it drops to 4 cylinders if you have a really loud exhaust, motor sounds completely different.
 

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It has been my experience in my 4X4 2009 Ram that the Fuel Saver Light = MDS mode. I have done tests on long straight roads without altitude changes where (on average) I cannot go over 48mph without kicking out of MDS mode.

Model year 2010 Trucks to current changed from the fuel saver text to ECO text. I'm told the ECO light means that you are driving in a fuel efficient manner and it doesn't necessarly mean your in MDS mode. Which in my mind just confuses the consumer in believing they are in 4 cylinder mode at higher speeds.
 

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The "ECO" light comes on when you are driving in an efficient manner and you may or may not be in MDS mode. I can tell when my MDS is operating because the RPMs drop a bit and there is a kind of shutter going on. I can only really tell when the speeds are down below 60 km/hr or so.
 

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mds addvice

when the fuel saver light comes on it means your in fuel saver mode ; which means your in 4 cyl mode . on my 09 I can tell right away , because as you said I also get a shudder so I know it's in the mds mode . heres a trick no matter if it;s cold or hot and your not in 12345 gears showing ; the arrow is green you will go into mds mode , kick it down to 12345 gear and it wont go in to mds mode till you go past the 5 and then your in mds mode unless you press down on acc enough to kick it out . so if you want to stay out of mds mode leave it in 5 or lower . also stay with the 5 - 20 0il , anything higher like 10 20 or 30 will mess up the valve that changes it to mds mode . happy new years all :smileup:
 

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Discussion Starter #9
Im wondering if the guy that owned my truck before used the wrong oil. The best i could get for gas mileage was about 16.5 mpg and that is driving the prairies at 105 kmph. I did an oil change 2 weeks ago and i started getting around 18-21 mpg. This is with 3.92 gears. The truck runs at 1900rpm at 110kmph. My buddy's truck with the 3.55 gears only tachs at 1650 at 110km so that is why he generally gets better mileage then me.

I have always been the told Fuel Saver light means nothing to do with the MDS. The light comes on if the truck is cold or hot and in any gear. I was told it just means your driving efficiently. I don't get the change in tone in the exhaust or get a shutter when MDS kicks in. I watch the tach like a hawk and even sat in the box of the truck and had my wife drive it and see if i could here any difference in the exhaust" Ha i really wanna know"
 

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the rpm,s dont change as the Eng goes into mds mode because your doing the same rpms in the mds mode .only dropping off cyl rpm remain the same .
 

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ECO light is NOT MDS. The ECO light comes on at very low speeds in the city if you are light on the throttle. MDS is not kicking it at those speeds. I can clearly feel the MDS when it does kick in - slight change in exhaust note and the slight shudder in the cabin from the engine. You can feel that happen, and it's nothing to do with the ECO light in the EVIC.
 

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mds modes

the rpms will remain the same when going into mds mode as the eng is still turning the same rpms . I have a 09 I have the shutter in the mds mode only when I give it a slight throttle up with out kicking it out of mds mode . as far as being on the free way and havering it change back and forth between the mds and full mode hard too tell as there's a very slight I mean a very slight hesitation . also on mine if your staring from a stop above 5 it will go into mds mode at any speed when you hold a steady speed , click it down to 5 or under and it don't [[[ the 5 being the trans gear shifting read out:smiley_thumbs_up: but then all tr are different uh ?
 

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ECO light is NOT MDS. The ECO light comes on at very low speeds in the city if you are light on the throttle. MDS is not kicking it at those speeds. I can clearly feel the MDS when it does kick in - slight change in exhaust note and the slight shudder in the cabin from the engine. You can feel that happen, and it's nothing to do with the ECO light in the EVIC.
My ECO light comes on all the time while I'm cruising on the highway. As a matter of fact it comes on alot when I drive around town and along the country roads where the limit is 80 km/h.

Whether or not my MDS is kicking in I don't know, I'm getting pretty good mileage so far so I must be doing something right.
 

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Do all 2009 Hemi engines come equiped with the MDS? Ive never seen a fuel saver light come on....cuz im always rompin on it, ............but i can tell its in the mode....i got 19.2 miles to the gallon last week, at 65 miles an hour at roughly 1200 rpm , with very little pedal...and plenty of pickup when i mashed on it......
 

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Early 09's did not have a Fuel Saver light, or, they were not activated from the factory. Later 09 versions did have/were activated.

Somewhere down the line, the 'Later' year model RAMS went from Fuel Saver to ECO lights,,, (Not sure which year model they switched)

Still with me? Good!

I have a Cortex and can tell instantly via an abrupt change in the MAP reading when I'm in 4 or 8, (that, along with 36,000 miles of experince with this truck)

BEFORE I went in for a 'HVAC' flash 2+ years ago, my FUELSAVER light was directly linked to the MDS.

IMMEDIATELY AFTER the flash, the dayum thing was no longer linked to MDS, and was activated by 'conservative driving'. As I do a lot of stop and go / conservative driving, the dayum FUELSAVER light stayed on so much, I considered it to be pretty much useless, so I deactivated it in the EVIC.

Now, that should clear up all the "does" and "does not" discussions we are having here, right!?!?

LMAO!!!!
 

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If you cannot tell when you are in MDS then your vehicle is running seamless as they advertise the MDS system as it works on mine. I cannot for the life of me hear any difference in the engine but I can see the tach changes shortly after the Fuel Saver light goes on. It is supposed to be quiet and seamless as I have noticed and my mileage is on target so feel good, I think the early build 09's are better JMHO.
 

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i have an 07, but im used to driving a z28 and a gixxer, both of which are MUCH louder than my ram. I think thats the reason i cant tell when mds is on or off.
 

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Mds on?

On my '09 SLT Quad Cab, I feel/see/hear a difference in the engine/rpm/exhaust note (standard exhaust) when MDS keem to go down a few hundred, engine smoothes out/goes quieter, but when a small ridse in elevation (going over an overpass or slight incline) the engine picks up (no downshift) in rpm's (only a couple hundred) and feels a slight "surge in power (the other four cyls kicking in?) then after the apex of the "climb" power then kicks out and rpm's drop a couple hundred. Hiway driving nets 20+ mpg with 500 mi per tank indicated on EVIC (but actual calc yields right at 20 mpg), with a 26 gal fuel tank Hemi. Just my take.
 

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Especially when cold, during a 'very light accelleration' event, I can also feel a surge when going from 8 to 4.
The single physical act of going from 4 to 8 or back doesn't change the rpms, but the loading of the engine, and how the engine / tranny reponds to that loading can, at times, have a small affect on rpms. It's all computer controlled/fly-by-wire,,,
All in all, it is pretty seamless, and the biggest indication I have of the change other than my Cortex is exhaust tone
 
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