The Multiple Displacement System (MDS) provides cylinder deactivation during steady speed, low
acceleration and shallow grade climbing conditions to increase fuel economy. Both four and eight
cylinder configurations have even firing intervals to provide smooth operation. The MDS selectively
deactivates cylinders 1, 4, 6, and 7, to improve fuel economy. All deactivated cylinders have unique
hydraulic lifters that collapse when deactivated to prevent the valves from opening. Engine oil
pressure is used to activate and deactivate the valves. Oil is delivered through special oil passages
drilled into the cylinder block. The MDS solenoid valves control the flow. When activated, pressurized
oil pushes a latching pin on each MDS lifter which becomes a lost motion link. The base of the MDS
lifter follows the camshaft while the top remains stationary. The MDS lifter is held in place against the
pushrod by light spring pressure but unable to move because of the much higher force of the valve
spring.
NOTE:
It is critical to use the recommended oil viscosity in engines that use MDS.
Deactivation occurs during the compression stroke of each cylinder, after air and fuel enter the
cylinder. Ignition occurs, but the combustion products remain trapped in the cylinder under high pressure, because the valves no longer open. No fuel/air enters or leaves during subsequent piston strokes, this high pressure gas is repeatedly compressed and expanded like an air spring.
