What Is Active Fuel Management?
Surprisingly, the concept of active fuel management has been around for over seven decades, first appearing in the 1940s in WWII for use on military vehicles. These initial experiments helped form the backbone for the first commercialized active fuel system used in the 1981 Cadillac L62 V8-6-4. A standard feature on all Cadillac models, except the Seville, the Cadillac L62 used the industry’s first engine control unit to switch the engine from 8- to 6- to 4-cylinder operation depending on the power needed. Unfortunately, the system was troublesome and misunderstood by customers which sent engineers back to the drawing board to develop a better system.
Forward to present day, engineers have solved the problems with the technology and active fuel management systems are commonly found on millions of production vehicles. The simple idea behind cylinder deactivation is that an engine’s full power is only typically needed while accelerating or performing engine-taxing activities like hauling a trailer or driving up steep hills. But when a vehicle is cruising on a highway with only a light load, shutting down several engine cylinders and turning them back on only when there’s a demand for more power can significantly increase fuel economy. In modern-day vehicles the two main types of cylinder deactivation systems common found are:
This technology uses solenoids to alter the oil pressure delivered to the lifters. In their collapsed state, the lifters are unable to elevate their companion pushrods under the valve rocker arms, resulting in valves that cannot be actuated and remain closed.
Overhead Cam Designs
This design employs a pair of locked-together rocker arms for each valve. One rocker arm follows the cam profile, while the other actuates the valve. When the cylinder is deactivated, solenoid-controlled oil pressure releases a locking pin which unlocks the rocker arm so it’s unable to activate the valve.
Common Symptoms of Failure
A malfunctioning fuel management system can be difficult to diagnose as there are a lot of moving pieces in play to make the technology work. A common culprit for a failed system is a bad cylinder deactivation manifold. To determine if it’s faulty, look for the following symptoms to know if it’s time to change it out for a new one:
- Power loss or rough idle
- Engine misfires
- Diminished fuel economy
- Triggered check engine light
Why Do Cylinder Deactivation Manifolds Fail?
The most common reason for failure is sticky lifters. Varnish from the fuel or oil sludge gradually builds up and carbonizes, causing the lifters to stick on or off. This failure results in the inability of the power-train control module (PCM) to properly activate or deactivate the engine cylinders.
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Photo courtesy of Wikimedia Commons.