Originally Posted by Jackdashack
I guess generally speaking if you are going 60 and the ECO light is on and you have the option in the EVIC like mine does of real time MPG and your getting 25/26mpg ... one would assume it's running on 4 cyl ... not 8 cyl
Not necessarily, but 95% of the time if your feathering the gas and the ECO light is on the MDS will kick in. Here is a simplistic view of how and when MDS will kick in, also remember that this may be different for other vehicles, due to the weight of the occupents, the road the temperature, humidity etc. All these things will affect how MDS will chime in,
- MDS will activate at as little as 18 mph, but you really have to pussyfoot the throttle for it engage. It will activate when off the throttle, as long as rpms remain above about 1100 or 1200rpm. If your coasting as the truck slows down the MDS will activate until the rpms pass below around 1200rpm, then you're back on all 8 cylinders. MDS will activate whenever the load permits, and above about 1200 rpm. MDS will function at pretty well any speed above 10-20mph and there is no set limit at which MDS will function, but you have to factor in the load on the engine so with a super strong back wind it might very well activate at 100 mph, (I said Strong Back wind like your running away from a hurricane).
Some have reported MDS will activate only at specific speeds, seems it will activate a lot at speeds of 25-35 mph, but once the transmission shifts into 4th gear (around 35 mph), it won't activate again until a little above 40 mph. MDS will then be very active in the 45-65 mph range. As speed increases above 65 mph MDS will rarely activate due to the aerodynamic drag which in turn will place a greater load on the engine. it can activate at speeds higher than 65, but you won't see it activate a lot at those speeds unless you've got a tailwind or are heading slightly downhill.
During all the time that MDS will Activate and de-activate, the ECO light will also turn on and off to distract you as you drive down the road but is not an indicator that MDS is on or off.