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30 Posts
Discussion Starter · #1 ·
On other cars, such as GM, when their version of MDS is engaged, a light comes on. We don't have that on Jeeps.

So, is there some sort of aftermaket gaget that can, say listen for the cylinder to stop firing (MDS engaged) and hit a light or tone within the cabin?

Inquiring minds want to know.

On a trip to Chicago, I was getting a 17.x MPG. I stopped to fill up before I got in the metro area. When I pulled back on the highway, the speed limit dropped to 55 MPH and traffic was keeping at 55. After 45 minutes, to my supprise, I was now getting 20.7 MPG. Obviously, MDS was engaged.

The word has been that MDS can be enabled between 40 and 60 MPH. Bogus in my opinion as who drives 55 across the country?

Anyway, it really showed that MDS does really help gas mileage. If I knew when MDS was on (and more importantly, when it kicks off), I might be able to modify my driving habbits to get the gas mileage.


170 Posts
Yep, MDS only works between the speeds of 40-60mph...yes, it does work well at those speeds to increase gas milage...but who drives under 60 on the highway during road trips??? LOL
Its kind of funny, the salespeople tell you it works at any speeds as long as your not towing or acclererating and Jeep markets it that way as well, you have to read the literature to find out how it actually does work.
I like to use MDS while on the in-town highway. Just using it on the in town freeways canboost my in town weekly gas milage to 17mph..not bad for intown driving.

476 Posts
Yep... MDS is an "enhancement" to the HEMI to allow for better mpg. I have it and really wish they would have left well enough alone. IFyou are going to get a HEMI... then you should get a HEMI... not some scaled down version. I will admit that oveall performance is very good and the power is certianly there when you need it... however, it seems a little sluggish when MDS is engaged.

...Also, due to the roads I take for my commute I am either traveling below 35 or above 70 MPH.... so it really does not do me much good.

398 Posts
This is from WKjeeps (Looks to be from some sort of official document) which is the best description I have seen. This is also the only place I have seen it stated that MDS is enabled between 20 and 80 mph. It may be a large misconception that it is only active between 40 and 60 MPH which is the speeds which I have seen commonly quoted (or misquoted).

At the bottom is also suggests a method from which you could add an MDS activation LED or light.

About the HEMI Multi-Displacement System:
Chrysler Group was the first to offer modern, large-volume vehicles in North America with cylinder deactivation - the HEMI-powered 2005 Chrysler 300C and Dodge Magnum R/T went on sale in the of spring 2004 with the Chrysler Group Multi-Displacement System, or MDS. Chrysler Group was also the first to offer cylinder deactivation in an SUV with the introduction of MDS in the 2005 HEMI-powered Jeep® Grand Cherokee. Chrysler Group is the first to offer MDS in a pickup truck - the 2006 Dodge Ram 1500.

The Chrysler Group MDS is standard equipment with the 5.7L HEMI on seven vehicles: the Chrysler 300C, Dodge Charger R/T, Durango, Magnum R/T, Ram 1500 and Jeep Grand Cherokee and Commander.

With the addition of MDS to HEMI-equipped Dodge Durango and Ram, MDS-equipped vehicles through the end of the 2007 model year will save more than 60 million gallons of fuel each year.

The Chrysler Group MDS (Multi-Displacement System) seamlessly alternates between smooth, high fuel economy four-cylinder mode when less power is needed, and V-8 mode when more power from the 5.7L HEMI® engine is in demand," said Eric Ridenour, Executive Vice President Product Development, Chrysler Group. "This optimizes fuel economy when V-8 power is not needed, without sacrificing vehicle performance.

The MDS was part of the engine's original design," said Bob Lee, Vice President Powertrain Product Team, Chrysler Group. "This resulted in a cylinder-deactivation system that is elegantly simple and completely integrated into the engine design. The benefits are fewer parts, maximum reliability and lower cost.

Some of the significant technologies enabling the Chrysler Group MDS are the speed of electronic controls, the sophistication of the algorithms controlling the systems and the use of Electronic Throttle Control. The HEMI will be able to transition from eight cylinders to four in 40 milliseconds (0.040 seconds).

The HEMI engine with MDS has completed over 6.5 million customer- equivalent miles through Chrysler Group's development and durability testing. It is covered by the 7-Year/70,000-mile Limited Powertrain warranty.

The system deactivates the valve lifters. This keeps the valves in four cylinders closed, and there is no combustion. In addition to stopping combustion, energy is not lost by pumping air through these cylinders. For proper operation, 5w-20 oil must be used in engines with the MDS feature. Failure to do so may result in improper operation of the Multiple Displacement System.

Customers will experience estimated fuel economy gains of up to 20 percent under various driving conditions, and a projected 10 percent aggregate improvement. Improved fuel economy is realized without any change in customer experience -- drivers will receive the benefit without changing their driving habits and without compromising style, comfort or convenience.

MDS components and operation

When all criteria has been met, power is supplied to each MDS Solenoid when the engine is making a transition from 8 cylinder mode to 4 cylinder mode. By actuating the solenoid, oil pressure is raised to the pair of lifters that coincide with each particular solenoid. The oil pressure pushes in the locking pins that allows the lifter to collapse, decoupling the valves and camshaft.

The Multi Displacement System selectively deactivates cylinders 1,4,6, and 7, to improve fuel economy. It has two modes of operation:

8 cylinders for acceleraton and heavy loads.
4 cylinders for cruising and city traffic.
The main components of the Multi Displacement System are:

Unique MDS camshaft.
Deactivating roller tappets.
4 control valves/solenoids.
control valve/solenoid wiring harness.
oil temp sensor.


NOTE: Vehicles with the 5.7L Multiple Displacement System must use SAE 5W-20 oil. Failure to do so may result in improper operation of the Multiple Displacement System.

The MDS system is designed to operate at speeds from around 20 mph to 80 mph. Some owners have reported activation at speeds up towards 90 mph. As shown in the chart below, the duty cycle is more active at highway speeds and on level ground. Other parameters that owners have discovered is that the engine operating temperature must be at least 130 degrees and oil pressure above 45 psi. In addition, the transmission must be in 5th gear at speeds above 35-40 mph.

MDS "activation lights" have been added by some owners. This involves wiring up a small light and switch to the No. 4 cylinder MDS solenoid power wire at the PCM pin # 28. While some people can determine the point when MDS is engaged or disengaged by the sound of the exhaust (more notably on aftermarket exhaust systems), the light provides more exacting results as to when the MDS system is on or off.

Cylinder Deactivation

Trap an exhaust charge
Normal combustion event
Don’t open exhaust valve
Don’t open intake valve
Piston is an air spring
Cylinders deactivated in firing sequence
Cylinder Reactivation

Empty the cylinder
Open exhaust valve
Open intake valve
Normal combustion event
Cylinders reactivated in firing sequence

Duty cycle: MDS was engaged for about 17% of city driving and 48% highway for an overall average of 40%

Maximizing MPG with MDS

Just a few simple tips can help owners of Chrysler Group engines with Multi-Displacement System (MDS) get the most fuel mileage possible from their 5.7L HEMI® V8 engine.

The customer does not need to drive in a certain way to realize a fuel economy improvement with MDS, but these driving habits can maximize their fuel savings with this technology.

Keeping speeds to 65 mph or below – MDS uses four cylinder mode most at these speeds
Use cruise control – this helps maintain a steady speed, generally allowing the HEMI to run on four cylinders for longer periods
Accelerate more gradually – the HEMI will provide V8 power whenever it is requested by the driver
Use a steady throttle whenever possible – this maximizes four cylinder mode

2,200 Posts
:42: I found the above post from SDBaja has some good info about MDS

186 Posts
My wife has a 2008 300C with the Hemi (which helped persuade me into getting the Commander with the Hemi). The MDS kicks in at all speeds of travel. We took a 160 mile "just for fun" drive last weekend. We drove 75 mph the entire time. Even though the terrain was hilly, the MDS was on 90% of the time. We got an astounding 25 mpg! Her car has a little visual bar graph that shows fuel consumption in "Performance" mode and "Economy" mode (MDS).
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