AFM relies on three primary components: De-ac (for deactivation) or collapsible valve lifters, a Lifter Oil Manifold Assembly (LOMA), and the ECM. AFM's response time varies with oil temperature, but in all cases is measured in milliseconds. Operation is virtually unnoticeable to the driver. The engine returns to V8 mode the instant the controller determines that acceleration or load requires additional power.
One of the most sophisticated engine controllers, the E38 ECM measures load conditions based on inputs from vehicle sensors and interprets that information to manage more than 100 engine operations, from fuel injection to spark control to electronic throttle control. AFM adds an algorithm to the engine control software to manage cylinder deactivation and reactivation.
Valve lifters are operated by the engine's camshaft and lift a pushrod that operates the valves in the cylinder head. In the Gen IV 6.0L (L76) engine, the De-Ac lifters are installed in cylinders 1, 4, 6 and 7, while the remaining cylinders use conventional lifters. The hydraulically operated De-Ac lifters have a spring-loaded locking pin, moved by oil pressure. For deactivation, hydraulic pressure dislodges the locking pin, collapsing the top portion of the lifter into the bottom and removing contact with the pushrod. The bottom of each De-Ac lifter rides up and down on the cam lobe but the top doesn't move the push rod. The valves don't operate and combustion in that cylinder stops. During reactivation, the oil pressure is removed, and the lifter locks at full length. The pushrods and the valves operate normally.
The final AFM component is the Lifter Oil Manifold Assembly, LOMA. This cast-aluminium assembly is installed in the valley of the engine in place of a conventional engine block cover. The LOMA holds four solenoids, control wiring and cast-in oil passages. The solenoids are managed by the ECM, and each one controls oil flow to a De-Ac Lifter, activating and de-activating the valves at one cylinder as required for Active Fuel Management.
The fuel injectors in the Gen IV 6.0L (L76) are identical for all cylinders; those feeding the de-activated cylinders are simply shut down electrically by the ECM during de-activation. When the cylinders are deactivated, the engine effectively operates as a V4. AFM operation is load based, measured by the ECM using dozens of inputs combined with your need for power which is registered by use of the throttle. AFM's response time varies with oil temperature, but is always measured in milliseconds and AFM in operation is virtually unnoticeable. The engine returns to V8 mode as soon as you determine that acceleration or load requires additional power.