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MDS/Eco Operational Questions

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dablack21

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How does the MDS/Eco function work on the 6.4? The only time I ever see it come on is when I am coasting down a highway, and how much fuel does that really save?? Is there a way to have it function when idling? I get a lot of idle time, and this thing chugs gas when idling, about a third of a tank in 6 or so hours
 
It comes on for me when coasting or under a light load...tooling around on a flat road at 55, it stays on most of the time.

The fuel savings is over the life of the vehicle.

No way that I'm aware to turn it on during idle..on the 1500 forum they were saying it is tied to the oil pressure so it won't kick on during idle, but I have no clue.
 
It's an annoying joke on a 7K lbs truck. Saves a thimble full of gas, if that. It cuts off half the cylinders, but the duration of the operating injectors doubles, so...
 
I got to ask why are you idling for 6 hours? We used to idle our work cars and of course got the memo from dodge saying hemi's should not be idled for long periods of time.
 
I’m wary about letting the Hemi idle for any extended period. I think that’s the best way to trigger the infamous lifter/cam issue. Got to give it a little gas to keep them properly lubricated.
 
MDS / Eco are different systems. The Eco light is just an indicator that the engine is running at high efficiency, it's just a feel-good dash light. It's not connected to the MDS, though. The MDS kicks on at low load with little to no acceleration, at speeds above 25 mph iirc. So you get to whatever speed you're moving at, the engine levels off around 1500 rpm, and MDS kicks on. MDS saves between 10% to 20% (tested) fuel when it's on, but that's only once you're at speed, of course. And it typically stops engaging at speeds around 65, depending on grade and wind resistance. I'm fairly sure that's mostly due to wind resistance being high enough that even at low rpms, the ECU is still sensing too much load. Going down a slight grade, MDS may kick on at higher speeds, even with a headwind. It seems to work mostly at speeds between 30 and 60. I find mine engaged a lot on country 2-lanes and not much at all on interstates. It does require oil pressure to run it - the lifters for the MDS cylinders are hydraulicly controlled. The Eco light is useless, best turned off. It goes on a lot when MDS isn't engaged, so it's not even a good telltale.
 
On my '15 2500 6.4 the Eco light 100% NEVER came on without MDS engaged, and vice-versa.
 
My 2015 is a 1500, and the Eco light comes on very early, at lower speeds than the MDS would engage. It comes on as I reduce acceleration, and at high speeds where the MDS doesn't engage at all. It's basically just an "attaboy, you're driving nice" light. I haven't seen much difference in my 2500.
 
1HasBeen said:
On my '15 2500 6.4 the Eco light 100% NEVER came on without MDS engaged, and vice-versa.
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I can EASILY get the ECO indicator light to come on without MDS being engaged on my 2017 2500 6.4.
 
jadmt said:
I got to ask why are you idling for 6 hours? We used to idle our work cars and of course got the memo from dodge saying hemi's should not be idled for long periods of time.
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I have a lot of start/stops at work. I hate shutting off for just a few minutes only to fire right back up and take off. Some of the time though, I will be idling for longer periods. And to be honest, if it's hot outside, I want to have some AC going and some heat in the winter.
 
Jimmy07 said:
I can EASILY get the ECO indicator light to come on without MDS being engaged on my 2017 2500 6.4.
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Different programming strategy I guess. My '15 absolutely did not do that in @43K miles I had it.
 
Jimmy07 said:
I can EASILY get the ECO indicator light to come on without MDS being engaged on my 2017 2500 6.4.
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Maybe something changed with the 2017. On my 2016 2500 6.4, the rare times that MDS kicks on for me, the ECO indicator always shows up at the exact same time. I've never seen/heard one without the other.
 
Ram and Chrysler have been putting economy indicators in their vehicles going way back, well before MDS existed. Usually the "economy" condition in most of their designs was based on engine intake vacuum level. In the 60s, a turn signal light in some vehicles was tied to the vacuum feedback. In the 1500 line, the Eco light comes with several engines. An experienced service guy told me on my 2015 (1500 w/ 5.7L Hemi) that it was just a vacuum sensor light, lets you know you're running at high efficiency. It even apparently showed up on the EcoDiesel option, which definitely doesn't have MDS. I've seen in forums past where a guy asked why his Cummins had an ECU light if it didn't have MDS. I don't know if he was serious or pulling someone's leg.
 
Yes, on the 1500 the Eco light and MDS work independently.
 
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