You think it'd be a desirable feature if eco-mode could also be manually selectable? (at least in the lighter vehicles carrying a v8, like the charger or something).

 

I would love to have a button that says, "I'm not pushing it. Use eco mode as much as possible."

 

I did some experimenting yesterday. I have the "eco" light turned off generally, but yesterday I turned it on.

My conclusion is that the "eco" light and MDS are not synonymous. I can tell because with my exhaust it's very clear at lower speeds under light load when MDS is active and when it's not. In fact, I usually put the gear selector in 6,7 or 8 unless I'm on the highway because of how annoying it is.

I believe that the "eco" light is just a visual reminder that you're operating efficiently. While it was always on when MDS was active, I also saw it on when MDS was not active; sometimes it was just a second or two, but at one point it was a good 15-20 seconds.

 

I have been doing the same thing over the last week. dwaldmann is right. I think the mds is ultimately activated when your throttle is at a certain position and I also think it reads to load on the motor via vacuum.... I can get the mds to kick on at highway speed (70mph) but only on flat ground... and very very light throttle... almost to the point where you can almost feel the truck struggling to maintain speed on 4 cylinders... as soon as there is too much throttle..or the load becomes to great and the motor bogs..the mds kicks off and all 8 cylinders light up

 

Yes, Eco mode and MDS are not the same thing. Eco mode only tells you you are driving in a fuel efficient manner. MDS mode runs on 4 cylinders. The catch is, you will never be in MDS mode unless you are driving in a fuel efficent manner.

I will say that running on four cylinders will not use more fuel than 8 cylinders. Think about it, those four cylinders would have to be using more than twice the amount of fuel to get less mileage, not to good for the cylinder walls. Rpm's for 8 and 4 are nearly identical.

If the rear end in your truck is a 3.21 you will not be in MDS mode as much as a 3.55 or a 3.92.





From AutoInc.online:

How Chrysler's Multiple Displacement System Works

Posted 10/12/2009
By Greg Montero

In 2005, the Multiple Displacement System (MDS) version of the 5.7L HEMI engine was introduced on the Chrysler 300C and Dodge Magnum. This engine can deactivate four of the eight cylinders, and operate as a 4-cylinder engine during periods of low load, improving fuel economy and emissions. The MDS provides the 5.7L engine the fuel economy of a V6 while maintaining the performance of a V8. The fuel economy improvement is estimated to be up to 20 percent, depending on driving conditions. The MDS operation, invisible to the driver, is fully integrated into the fuel injection system.

"In 2005, the Multiple Displacement System (MDS) version of the 5.7L HEMI engine was introduced on the Chrysler 300C and Dodge Magnum. This engine can deactivate four of the eight cylinders, and operate as a 4-cylinder engine during periods of low load, improving fuel economy and emissions.”

When the MDS engine switches to 4-cylinder mode, the powertrain control module (PCM) controls solenoids that manage special "dual mode" lifters, allowing the intake and exhaust valves to remain closed on cylinders 1, 4, 6 and 7. There is one solenoid for each cylinder (two lifters). The PCM also deactivates the fuel injectors for these cylinders when in the 4-cylinder mode.

When the MDS solenoids are in the "off" state (8-cylinder mode), they supply oil pressure of approximately 3 psi to the lifter bores. This lifter oil keeps the bores lubricated and prevents air from entering the system. When the solenoids are activated, oil pressure of 16 psi or greater is supplied to the lifters and the engine enters the 4-cylinder mode.

When the special lifters are supplied high oil pressure by the solenoid, pins inside the lifter move inward. This unlocks the outer portion of the lifter and allows it to move independently from the center portion of the lifter. The camshaft can move the outer portion of the lifter without transferring motion to the inner portion of the lifter.

8-cylinder mode: Solenoids are in the "off" state (de-energized). Minimal oil pressure is applied to the special lifter. They are working normally in this mode.

4-cylinder mode: Solenoids are in the "on" state (energized). High oil pressure is applied to the special lifters and the lifters become inactive and essentially the four pistons are along for the ride. Both valves are closed.

The PCM will activate the 4-cylinder mode when the following enabling conditions are met:

Low engine load

1200 to 3000 rpm

Vehicle speed between 12 mph and 90 mph

Battery voltage from 9 volts to 15 volts

Oil pressure from 15 psi to 147 psi

Oil temperature greater than 120 F

Engine coolant temperature from 158 to 248 F

Ambient temperature from 14 F to 248 F

No throttle position sensor or MDS faults

The PCM deactivates solenoids one cylinder at a time in the firing order. If the system is "on" for long periods of time, such as a long flat road with no stopping, the system will return to the 8-cylinder mode approximately every six minutes to maintain engine temperature. The PCM will also unlock the torque converter before the transition, to minimize the effect on driveability.

The oil temperature sensor used for this system is a two-wire sensor, negative temperature coefficient, like the sensors for engine coolant temperature or intake air temperature (IAT). The PCM uses this input - along with oil pressure, load and rpm - to calculate oil viscosity and flow rate. This information is critical to MDS operation.

It's important to know this engine uses 5W-20 engine oil. If the wrong oil is used, fault code P1521 can be set, and the vehicle may show symptoms of a shudder - similar to a torque converter shudder - when the MDS system is activated and deactivated. Other symptoms may include MDS performance codes or engine misfire codes.

Before spending a lot of time with these codes, use the vehicle service history to find out what type of oil is in the engine. Because this is not always possible, the next best thing is to replace the oil (and filter) with 5W-20. This may have to be done twice to fully restore the system back to normal. Oil sludging, restricted oil passages or lifter contamination can also cause problems with this system.

Quick facts:

Each MDS solenoid has about 12 ohms of resistance. When the solenoid is activated by applying 12 volts to it, an audible "click" can be heard from under the intake manifold. This test can be done with a jumper wire or by using the actuator test mode (ATM) mode of a compatible scan tool.

If the solenoid is mechanically stuck in the "on" position, the result will be one dead cylinder.

Hopefully, this information will be helpful if one of these systems shows up in your shop.

There has been some tweeking of the system over the years since this was posted and I don't have any information on those but it was adjusted to engage over a bit wider range from what is posted.

 

Some trivia: The first Gen 4 Rams (early MY 09) did not have the "ECO" indicator. When MDS was operating in these early trucks, a "Fuel Saver" readout is present in the vehicles EVIC. The "Fuel Saver" indicator is directly linked to MDS operation.

Cheers,

Keith

 

That is interesting, where did you hear this?

My "Fuel Saver" light will come on with a cold engine, well below the threshold for MDS to be active. My truck originally had no "Fuel Saver" light and had to be added with a flash update in July 2009. Truck is a September 2008 build.

 

I have the console shifter and almost always shift to ERS to avoid MDS. Lol

I've noticed that if I move the shifter to ERS, from D, (under load) -- the gear selected is usually 1 or 2. The next trip when I move the shifter to ERS, from D (with my foot off the pedal) -- the gear selected is 5. I'm usually running around 20 mph under both conditions.

Not complaining, just saying...

 

Just the way my particular truck operates. Early Dec 08 and prior engines with EZD sales code had no light/indicator. Late Dec 08 EZH engines introduced the "Fuel Saver" indicator on the right side of the ODO section of the EVIC. Interestingly, there is nothing in the my owner's manual (3rd edition) on this feature. It shows up in the 4th edition of the 09 manual.

That was TSB 08-007-10. Where does your fuel saver light appear in the EVIC? Does it present as "Fuel Saver" or "ECO"?

 

I do too. Especially since it's (MDS) become so obnoxious.

That's normal. When selecting ERS, the transmission will always jump to the gear that the transmission was in prior to selecting ERS.