To provide maximum fuel economy under light load driving conditions, the engine control module
(ECM) will command the displacement on demand (DOD) system to deactivate engine cylinders 1
and 7 on the left bank, and cylinders 4 and 6 on the right bank, switching to a V4 mode. The
engine will operate on 8 cylinders, or V8 mode, during engine starting, engine idling, and medium
to heavy throttle applications.

When commanded ON, the ECM will determine what cylinder is firing, and begin deactivation on
the next closest DOD cylinder in firing order sequence. The Gen IV engine has a firing order of
1-8-7-2-6-5-4-3. If cylinder number 1 is on its combustion event when DoD is commanded ON, the
next cylinder in the firing order sequence that can be deactivated is cylinder number 7. If cylinder
number 5 is on its combustion event when DoD is commanded ON, then the next cylinder in the
firing order sequence that can be deactivated is cylinder number 4.

Cylinder deactivation is accomplished by not allowing the intake and exhaust valves to open on the
selected cylinders by using special valve lifters. The deactivation lifters contain spring loaded
locking pins that connect the internal pin housing of the lifter to the outer housing. The pin housing
contains the lifter plunger and pushrod seat which interfaces with the pushrod. The outer housing
contacts the camshaft lobe through a roller. During V8 mode, the locking pins are pushed outward
by spring force, locking the pin housing and outer housing together causing the lifter to function as
a normal lifter.

When V4 mode is commanded ON, the locking pins are pushed inward with engine oil pressure
directed from the valve lifter oil manifold (VLOM) assembly solenoids. When the lifter pin housing
is unlocked from the outer housing, the internal pin housing will remain stationary, while the outer
housing will move with the profile of the camshaft lobe, which results in the valve remaining closed.
One VLOM solenoid controls both the intake and exhaust valves for each deactivating cylinder.
There are 2 distinct oil passages going to each DoD lifter bore, one for the hydraulic
lash-adjusting feature of the lifter, and one for controlling the locking pins used for cylinder
deactivation.
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Engine Displacement On Demand Operation (DOD)