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MDS - A Brief Overview

24K views 39 replies 24 participants last post by  Risk 
#1 · (Edited)
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 providesmooth 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.

NOTE: It is critical to use the recommended oil viscosity in 5.7L engines that use MDS.

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.






 
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#40 ·
I know this thread has been dead for quite some time but I didn't want to make a new thread for what should be a simple question:

what are the exact parameters for MDS engaging? The best explanation I can find is "under light loads" but how is that defined/tracked or monitored?

When using bluedriver (a bluetooth obd2 scanner) I have a function that estimates engine load.. is there a percentage of load under which MDS should engage? I tried finding out how and when MDS was engaging and, on a stock system, can't tell if it ever comes on. Isn't idling a "light load"? why wouldn't MDS engage at idle? Just trying to understand the system better so I can make better informed decisions, thanks for your time.
 
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