Active Fuel Management (AFM) enables the engine to automatically operate on half its cylinders under light load conditions, improving fuel efficiency by up to 12 percent in some vehicles. When loads are light, the control system automatically closes both intake and exhaust valves for half of the cylinders, cutting off their air and fuel supply. The fuel supply resumes and the valves are reopened to provide all-cylinder operation when the driver needs it for quick acceleration or for hauling heavy loads.

In 2007, GM expanded application of its industry-leading AFM technology with the company's first V-6 in North America featuring AFM. The 3.9L AFM V6 (LZ8) debuted as an option in the 2007 Chevrolet Impala.

In 2008, more than 2 million vehicles with the V-8 and V-6 engines will feature Active Fuel Management.

How it Works

A sophisticated engine controller determines when to deactivate cylinders, allowing the engine to maintain vehicle speed in lighter-load conditions such as highway cruising. The process is seamless and virtually imperceptible. When the cylinders are deactivated the V-8 engine effectively operates as a V-4, with alternate cylinders on each cylinder bank disabled. The engine returns to V-8 mode the instant the controller determines the vehicle speed or load requires additional power. When the V-6 engine is in AFM mode the left bank of cylinders are shut down. The key to AFM's efficiency and smooth operation is a set of special two-stage hydraulic valve lifters, which allows the lifters of deactivated cylinders to operate without actuating the valves.

The valve lifters have inner and outer bodies, which normally operate as a single unit. When the engine controller determines cylinder deactivation conditions are optimal, the outer body moves independently of the inner body on the disabled cylinders' lifters. The outer body moves in conjunction with camshaft actuation, but the inner body does not move, holding the pushrod in place. This prevents the pushrod from actuating the valve, thereby halting the combustion process. Solenoids in the engine lifter valley operate to deliver high-pressure oil to the switching lifters, activating a release pin to separate the inner and outer bodies. Oil circulation and pressure do not vary, regardless of the engine's operational mode. Lifter design and pushrod length are the same for every cylinder, but camshaft lobe profiles differ for cylinders designated to be deactivated.

The engine's electronic throttle control (ETC) also is used to increase manifold pressure in V-4 mode so that the engine can maintain a V-8 torque load.

2007 Model Availability [2008 Coming Soon]

Buick	Rainier
Chevrolet	Silverado, TrailBlazer, Suburban, Avalanche
GMC	Sierra, Envoy, Yukon, Yukon XL

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