Do you like your MDS?

[silver billet]

my trk is running at least 75% of the time with the MDS/Eco light ... so much i think this trk would operate here in the river hills of Pa with a 4 or 6 cyld motor and only needs this 6.4 when tow/hauling stuff ... and when my trk is idling the MDS light is not on

I'm just saying in my very light weight 1500 (1750 pounds of available payload, to give you an idea that it's almost as light as possible), it never comes on unless I am in 7th or 8th and have a tail wind, or if I'm slowing down it will slip on for a few seconds. I drive like a Grandma, I always hold my speed stable and steady.

I'm not sure which of your trucks you're referring to, but if you have 5.7 in a 2019 1500 and your truck is lighter than mine and your MDS is truly coming on 75% of the time, then (given all the user reports we have of how ineffective MDS is) we have a different issue, namely, these engines are built so poorly that there is a significant difference in how they perform, and I find that extremely concerning.

 

[RamSco]

I don’t like the MDS at all. When it kicks in, I feel it in my seat and in the gas pedal. The truck feels like it’s having trouble getting out of its own way. And with my tuned exhaust, it gurgles loudly. I disable it every time I drive.

 

[Gman]

MDS/Eco also won't engage under engine braking. I've seen this with steep downgrades here in Colorado. The instant economy still shows 99 MPG, but 8 cylinders pumping offer more resistance than 4.

 

[Gman]

I'm not sure which of your trucks you're referring to, but if you have 5.7 in a 2019 1500 and your truck is lighter than mine and your MDS is truly coming on 75% of the time, then (given all the user reports we have of how ineffective MDS is) we have a different issue, namely, these engines are built so poorly that there is a significant difference in how they perform, and I find that extremely concerning.

Since he mentioned the behavior of his 2500 and he also referenced the 6.4l Hemi, I think it's safe to assume that he's still referring to the 2500.

The more torque the engine has, the more effectively it can use MDS.

 

[slimchance]

I'm just saying in my very light weight 1500 (1750 pounds of available payload, to give you an idea that it's almost as light as possible), it never comes on unless I am in 7th or 8th and have a tail wind, or if I'm slowing down it will slip on for a few seconds. I drive like a Grandma, I always hold my speed stable and steady.

I'm not sure which of your trucks you're referring to, but if you have 5.7 in a 2019 1500 and your truck is lighter than mine and your MDS is truly coming on 75% of the time, then (given all the user reports we have of how ineffective MDS is) we have a different issue, namely, these engines are built so poorly that there is a significant difference in how they perform, and I find that extremely concerning.

actually both the 5.7 (wife's trk) and my 6.4 show the MDS/Eco mode on most of the time .... one example is a VERY steep hill leading up from the river, it is about 5 blocks long leading to Turkey Hill Dairy and has lots of big trk traffic .... in both trks (of course different times) we have followed big trks up this hill starting around 45 mph (Eco on) and near the top i am in 3rd gear, 15 mph and the ECO is still on .... only when i have to slow to allow the big trk to turn into the dairy does either of out trks downshift to 2nd and the ECO light goes off .... also another example is when towing (NO tow/haul) our 4,000# tandem utility trailer to the cabin with approx 500# UTC (total weight around 2000#s) and running up RT 322 toward State College, Pa the ECO light is on, either trk, most of the time ... i know this does not follow the line of conversation on this or other threads but this is how our stuff has worked

 

[silver billet]

actually both the 5.7 (wife's trk) and my 6.4 show the MDS/Eco mode on most of the time .... one example is a VERY steep hill leading up from the river, it is about 5 blocks long leading to Turkey Hill Dairy and has lots of big trk traffic .... in both trks (of course different times) we have followed big trks up this hill starting around 45 mph (Eco on) and near the top i am in 3rd gear, 15 mph and the ECO is still on .... only when i have to slow to allow the big trk to turn into the dairy does either of out trks downshift to 2nd and the ECO light goes off .... also another example is when towing (NO tow/haul) our 4,000# tandem utility trailer to the cabin with approx 500# UTC (total weight around 2000#s) and running up RT 322 toward State College, Pa the ECO light is on, either trk, most of the time ... i know this does not follow the line of conversation on this or other threads but this is how our stuff has worked

I'm not suggesting that's not how it works in your trucks, but for the vast majority of us it appears that even when the truck sniffs an ant hill 2 miles yonder, it stops working. I have over 12,000 KM on my truck at this point, so it's not exactly brand new and can't be written off as "braking in" anymore.

MDS/Eco also won't engage under engine braking. I've seen this with steep downgrades here in Colorado. The instant economy still shows 99 MPG, but 8 cylinders pumping offer more resistance than 4.

Again I find your comment worriesome, because actually mine does stay on when I go down a long hill with engine braking. It stays on 100% of the time down a hill. And if I hit the "-" rev limiter to force MDS off, and the 1 or 2 times I tried it I don't believe I noticed any difference in braking power, the engine braking is just as effective with 4 cylinders vs 8, only the noise is noticeably different. I will retest next time I'm there.

 

[Gman]

I'm talking about 6 & 7% grades with engine braking.

I notice MDS engaged quite a bit of the time in the low to mid-40 mph range and it will stay engaged on a gradual uphill climb.

Much of what you can experience with MDS engaging has to do with your right foot. You can encourage it to engage by easing the throttle and you can keep it engaged with very subtle inputs.

 

[slimchance]

"because actually mine does stay on when I go down a long hill with engine braking. It stays on 100% of the time down a hill. "
guess our 3 new rams are the exceptions ... on long down hills with engine braking the MDS/ECO light goes off as i believe it should

 

[StuartV]

MDS/Eco also won't engage under engine braking. I've seen this with steep downgrades here in Colorado. The instant economy still shows 99 MPG, but 8 cylinders pumping offer more resistance than 4.

Are you saying that when MDS is on, 4 of the pistons stop moving?

 

[Gman]

No, from what I understand, the valves close and those cylinders act like an air spring. Deactivated cylinders are in balanced phases of compression and expansion so that they counteract each other.

 

[mdemuysere]

No, from what I understand, the valves close and those cylinders act like an air spring. Deactivated cylinders are in balanced phases of compression and expansion so that they counteract each other.

This is essentially correct.

 

[jim888]

The only way I can tell if mine is in 4cyl mode is if the eco light is on.

 

[RSConsulting]

From another forum - from a (supposed) Ram Tech:

The Multiple Displacement System (MDS) provides cylinder deactivation during steady speed, low acceleration and shallow grade climbing conditions to increase fuel economy. Both four and eight cylinder configurations have even firing intervals provide smooth operation. Two cylinders on each bank are active when the engine is in four-cylinder mode – every other cylinder in the firing order. All of the cylinders that are deactivated have unique hydraulic valve lifters that collapse when deactivated to prevent the valves from opening. Engine oil pressure is used to activate and deactivate the valves. It is delivered through special oil passages drilled into the cylinder block. Solenoid valves control the flow. When activated, pressurized oil pushes a latching pin on each valve lifter, which then becomes a “lost motion” link. Its base follows the camshaft, but its top remains stationary, held in place against the pushrod by light spring pressure but unable to move because of the much higher force of the valve spring.

NOTE: It is critical to use the recommended oil viscosity in 5.7L engines that use MDS.

Deactivation occurs during the compression stroke of each cylinder, after air and fuel enter the cylinder. Ignition then occurs, but the combustion products remain trapped in the cylinder under high pressure, because the valves no longer open. No air enters or leaves. During subsequent piston strokes, this high-pressure gas is repeatedly compressed and expanded like an air spring, but fuel is not injected.

Anything that decreases my fuel consumption (currently at 13.7, 2,000 miles) is just fine by me. It activates at the weirdest times. But comes off pretty quick when I get back on the pedal. Now, if it would work cruising the interstate at 75 - I'd be a happy camper. I also initially found the stop/start to be annoying - but with the Etorque motor, it's much less so than my '16 Honda Pilot (which used the starter motor to restart). I always disabled it on the Honda - but I'm leaving it enabled on the Ram, as it might just save me a few $$'s in the long run -and it's not as "herky jerky" as it was in the Honda.

My $.02

Rick

 

[Firebird]

The only way I can tell if mine is in 4cyl mode is if the eco light is on.

My 6.4 was that way, seamless. But the 5.7 in my new truck is not. I don't use MDS in the city anyhow, so doesn't bother me. I do use it on the hwy, and it performs well there.

 

[Ram4141]

When mine comes on it is seamless. The problem I see with mine is it hardly ever comes on. If I am driving on the interstate it will only come on if I am going down a slight grade and I am basically coasting. Any gas pedal press at all and it cuts right off. My previous Gen 4 '16 was always on when I was cruising on the interstate.

 

[DraKhen99]

I would guess that MDS is active on 10-15% of my driving. I have gotten my truck to upshift and accelerate (albeit slowly) without kicking back into 8-cylinder mode.

-John

 

[jabara572]

Mine is on a solid 50% of the time. You really need to drive like your foot is a feather to keep it on, anything over 5-7% throttle or so it will kick off. You will also see it much more if you use that hemi like a hemi and gas it off the line and get up to speed, then ECO will kick on.

If you drive like a grandpa and slowly accelerate up to speed you may never see it. GIve it the boot and get up to speed and coast. BMW did studies in the 80's for the 5 series and that was the most economical way to drive (at least the 5 series, probly a stick).

Several of us have commented they probably should have widened the parameters to keep MDS on more, but also remember there will be some situations where running all 8 is more actually efficient than try to dog out the engine on 4 cyl.

 

[slimchance]

i "drive like a grandpa " cause i am .... my MDS is on most of the time .... here in the river hills of PA ... i sometimes wonder if i bought a 6.4 hemi or a 3.2 hemi ... but it does work great for this 70 yr old grandpa

 

[76poptop]

When mine comes on it is seamless. The problem I see with mine is it hardly ever comes on. If I am driving on the interstate it will only come on if I am going down a slight grade and I am basically coasting. Any gas pedal press at all and it cuts right off. My previous Gen 4 '16 was always on when I was cruising on the interstate.

Mine is the exact same, honestly a little bummed out I don’t see it, doesn’t matter if I’m cruising at 65-80 the only time it comes on is if I’m “coasting” downhill.


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[NDanecker]

I hate it. I usually lock out 8th gear so MDS is turned off. Although I've stopped tracking fuel mileage I did track tanks with MDS on vs. off with no real gain. Can't stand how it drives. Getting it removed during my engine rebuild.