General Motors Cylinder Deactivation (Active Fuel Management) engine control system has the ability, under certain light load driving conditions, to provide maximum fuel economy by deactivating three of the engines six cylinders. The engine will normally operate on six cylinders in V6 mode during starting, idling, and medium or heavy throttle conditions. When commanded ON, the powertrain control module (PCM) will direct the active fuel management (AFM) system and deactivate cylinders one, three, and five on the right bank.

The valve lifter oil manifold assembly (1) is bolted to the top of the engine block beneath the lower intake manifold assembly. The oil manifold consists of three electrically operated and normally-closed solenoids (2). Each solenoid directs the flow of pressurized engine oil to the Cylinder Deactivation (AFM) intake and exhaust valve lifters (3).

When enabling conditions are met for Cylinder Deactivation operation, the PCM will ground each solenoid control circuit in firing order sequence, allowing current to flow through the solenoid windings. With the windings energized, the solenoid valves open and direct pressurized engine oil through the manifold into six vertical passages in the engine block lifter valley. The six vertical passages, two per cylinder, direct pressurized oil to the valve lifter bores of the cylinders to be deactivated. When vehicle operating conditions require a return to V6 mode, the PCM will turn OFF the ground circuit for the solenoids, allowing the solenoid valves to close. When the solenoid valves are closed, remaining oil pressure is exhausted through the bleed passages of the manifold into the engine block lifter valley. The housing of the oil manifold incorporates several oil bleed passages that continually purge trapped air from the manifold and engine block.

To help control contamination within the Cylinder Deactivation (AFM) hydraulic system, a small replaceable oil filter (4) is located in the manifold oil inlet passage. This filter should be replaced, along with the LOMA gasket, anytime the LOMA system is removed. Refer to Lubrication Description and Cylinder Deactivation (Active Fuel Management) System Description for further information on Cylinder Deactivation operation.

When operating in V6 mode, the Cylinder Deactivation (AFM) valve lifters function similar to the non - Cylinder Deactivation (AFM) valve lifters. The Cylinder Deactivation (AFM) oil manifold solenoids are in the closed position with no pressurized oil directed to the valve lifters. The pushrod (1) travels upward and downward to actuate the rocker arm and valve. The spring loaded locking pins (5) of the lifter are extended outward and mechanically lock the pin housing (4) to the outer body of the valve lifter (3).

When the Cylinder Deactivation (AFM) system is commanded ON, the PCM will direct the solenoids of the oil manifold to open and direct pressurized oil to the valve lifters. Oil travels through the manifold and engine block oil galleries and enters the inlet port (6) of the valve lifter.

When operating in three cylinder mode, pressurized oil forces the locking pins (11) inward. The pushrod (7) remains in a constant position and does not travel upward and downward. The outer body of the lifter (9) moves upward and downward independently from the pin housing (10). The valve lifter spring (8) retains tension on the valve train components to eliminate valve train noise.

When the Cylinder Deactivation (AFM) system is commanded OFF, the PCM directs the solenoids of the oil manifold to close, stopping the flow of pressurized oil to the valve lifters. The oil pressure within the lifter will decrease and the locking pins will move outward to mechanically lock the pin housing and outer body.

The Cylinder Deactivation (AFM) engine block incorporates additional features to support Cylinder Deactivation (AFM) system operation. Engine oil pressure is routed from the number 3 cam bearing (1) to the oil manifold assembly. Cylinders one, three, and five each have two vertical, cast-in-block oil passages (2). The vertical oil passages permit oil flow from the oil manifold assembly to the valve lifter bores.

The LOMA oil manifold is not a serviceable item, and thus should be serviced as an assembly.

If it is found that one or more of the AFM lifters are not operating properly and needs replacing, replace all 6 AFM lifters and the lifter guide as an assembly.

Refer to Cylinder Deactivation (Active Fuel Management) System Description .