Valve Lifter Oil Manifold Assembly

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The cylinder deactivation system uses an electro-hydraulic actuator device called the valve lifter oil manifold assembly. The valve lifter oil manifold assembly is bolted to the top of the engine valley, below the intake manifold assembly. The valve lifter oil manifold assembly consists of 4 electrically operated normally closed solenoids. Each solenoid controls the application of engine oil pressure to the intake and exhaust valve lifters on the cylinders selected to deactivate. Engine oil pressure is routed to the valve lifter oil manifold assembly from an internal oil passage on the rear of the cylinder block.

All 4 valve lifter oil manifold assembly solenoids are connected in parallel to a fused ignition 1 voltage circuit, supplied by the powertrain relay. The ground or control circuit for each solenoid is connected to a low side driver internal to the engine control module (ECM).

When all enabling conditions are met for cylinder deactivation, the ECM will ground each solenoid control circuit in firing order sequence, allowing current to flow through the solenoid windings. With the coil windings energized, the solenoid valve opens, redirecting engine oil pressure through the valve lifter oil manifold assembly into 8 separate vertical passages in the engine lifter valley. The 8 vertical passages, 2 per cylinder, are connected to the valve lifter bores of the cylinders to be deactivated. When vehicle-operating conditions require a return to V8 mode, the ECM will turn OFF the control circuit for the solenoids, allowing the solenoid valves to close. With the solenoid valves closed, engine oil pressure in the control ports is exhausted through the body of the solenoids into the engine block lifter valley. The housing of the valve lifter oil manifold assembly incorporates several bleeds in the oil passages to purge any air trapped in the valve lifter oil manifold assembly or engine block.

To help control contamination to the hydraulic circuits, a small replaceable oil screen is located in the valve lifter oil manifold assembly oil inlet passage, below the oil pressure sensor. The oil pressure sensor is a 3-wire sensor which provides oil pressure information to the ECM.

During service, use extreme care in keeping the valve lifter oil manifold assembly free of any contamination or foreign material.

Cylinder deactivation may be inhibited for many reasons including the following:

Engine coolant temperature out of range for cylinder activation
Engine vacuum out of range
Brake booster vacuum out of range
Transmission gear incorrect or shift in progress
Accelerator pedal out of range or rate of pedal application to fast
Engine oil pressure and temperature out of range
Engine speed out of range
Vehicle speed out of range
Minimum time in V8 mode not met
Maximum V4 mode time exceeded
Decel fuel cutoff is active
Reduced engine power is active
Torque management is active
Catalytic converter over temperature protection is active
Piston protection is active, knock detected
Cylinder deactivation solenoid driver circuit faults