What Does Active Fuel Management Mean?

Active Fuel Management (AFM) engine technology shuts down some of the engine’s cylinders when they’re not needed to improve fuel economy.

AFM is a General Motors (GM) engine technology and is typically fitted on its V6 or V8 engines, which are usually found in high-performance sports cars or trucks that haul heavy loads. These large, powerful engines tend to consume more fuel. AFM deactivates half of the engine’s cylinders when driving conditions don’t require the engine’s full power, such as heavy traffic, driving slowly in residential neighborhoods, or cruising on the highway, to save on fuel. The engine can then reactivate the cylinders seamlessly when necessary.

AFM technology essentially allows trucks and sports cars to still have large engines that are more fuel efficient than ever before instead of having to rely on smaller engines with turbochargers or multi-valve cylinder heads.

How Does AFM Work?

An AFM-equipped engine deactivates cylinders by collapsing the corresponding valve lifters, which effectively stops the intake and exhaust valves from opening. At the same time, the corresponding cylinder’s fuel injectors and spark plugs will also stop working. The deactivated cylinders’ pistons still move up and down, but they’re just along for the ride.

How does deactivating engine cylinders result in fuel savings? Each piston in an engine uses up energy as it pulls in and expels air. This wasted energy is called pumping loss. By disabling the valves that pull in and expel air, an engine will have less pumping loss and run more efficiently.

AFM deactivates four cylinders in V8 engines and three cylinders in V6 engines. When the driver needs more power, the engine can reactivate the cylinder seamlessly by reengaging the valve lifter.

What Are the Advantages of AFM

The main benefit of AFM is better fuel economy. Deactivating cylinders can improve fuel economy by 5% to 7%.

What Are the Common Problems of AFM?

AFM-equipped engines have more parts compared to conventional engines, which means there are more parts that can wear out, fail, and cause problems. This is why there are programs and kits that allow vehicles to disable AFM since it can be a hassle if it fails. The AFM lifter is one of the main components that fail in an AFM-equipped engine. When an AFM lifter fails, the engine can jerk and hesitate when accelerating, stall suddenly, and have low power. In worst-case scenarios, it can even take out the engine camshaft. The engine might also have trouble downshifting.

Engines with AFM also need an abundant supply of clean oil to work properly. AFM issues typically stem from oil supply or oil pressure issues.

AFM-equipped engines might excessively consume oil or have fouled spark plugs. A technical service bulletin has also been published explaining that these engines might consume more than one quart every 2,000 to 3,000 miles. Additionally, higher mileage models can also have an illuminated check engine light and a rough running engine.

Contaminated engine oil can also prevent the locking pins and valve lifters from freely moving, which can cause misfires. There are also some reported instances of drivers feeling cylinders activate and deactivate when they’re supposed to be seamless.

Some AFM-equipped engines might be known to have issues, especially the ones in Chevrolet vehicles made from 2007 to 2011. If you own an AFM-equipped vehicle, you should regularly change your engine’s oil and have it serviced to prevent any issues.

Do Other Vehicle Manufacturers Have AFM?

AFM is GM’s name for its cylinder deactivation technology. Other manufacturers also have similar technologies but they market them under different names. Honda calls it Variable Cylinder Management, Jeep, Chrysler, and Dodge call it Multiple Displacement System, while Volkswagen calls it Active Cylinder Management.

A 5% to 7% improvement in fuel economy might not sound much, but this marginal gain can add up in the long run.