As noted above, there isn't anything you can do to "turn off" MDS except through software modification. Below is some information about how MDS works to help forum members better understand MDS operation.
The Multiple Displacement System (MDS) provides cylinder deactivation during steady-speed, low-acceleration and shallow grade climbing conditions to increase fuel economy. The Powertrain Control Module controls the operation of the MDS system. Primarily the engine must be warmed up to at least at normal operating temperature. This assures the oil is at the correct viscosity to flow to the solenoids properly. The PCM will determine if the required engine load will permit MDS operation.
MDS operates between 1,000 and 3,000 rpm. It will operate in four-cylinder mode when the torque requirement is less than 95 percent of the maximum available from four cylinders. It provides full-rated power in V8 form with an increased fuel economy benefit when operating in four-cylinder mode, depending on driving habits and vehicle usage. It is integrated into the basic engine architecture and is more reliable than add-on systems. Deactivation and activation of the cylinder is transparent to the driver.
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.
Special hydraulic lifters are used on four of the cylinders. They are controlled by solenoids. Each of the designated cylinders has its own solenoid which controls two lifters. When the solenoid is energized, oil under pressure is permitted to flow to the side of the lifter. This causes a lock pin inside the lifter to compress. When the lock pin is compressed the lifter contracts and its length is reduced. At its reduced length the lifter is no longer able to open the engine valve.
Both four- and eight-cylinder configurations have even firing intervals, providing 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.
720 degrees of crankshaft revolution is required to fire all cylinders. This is the same for all four stroke engines. When this number is divided by the number of cylinders, it produces, 90 for eight cylinders, 120 for six cylinders and 180 for four cylinders. Combinations of 90 and 180 work well together. The change occurs within two revolutions of the crankshaft. When operating in the economy mode, the engine is operating like an efficient four cylinder engine. With drive by wire there will be no change in the accelerator pedal position.
MDS can provide a 5-20 percent fuel economy benefit when operating in four-cylinder mode, depending on driving habits and vehicle usage. For EPA rating purposes, fuel economy is 8-15 percent higher than if the engine was operating on eight cylinders at all times.
MDS is integrated into the basic engine architecture, requiring a minimum of additional parts - four additional solenoids, an oil temperature sensor and a wire harness. Eight unique valve lifters and a modified camshaft are also required.
NOTE: It is critical to use the recommended oil viscosity in 5.7L HEMI engines that use MDS. Vehicles with 5.7L HEMI engines equipped with Multiple Displacement System (MDS) must use SAE 5W-20 oil. Failure to do so may result in improper operation of the Multiple Displacement System (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
