What Is Active Fuel Management & How Does It Work?
Active Fuel management (AFM) and Displacement on Demand (DOD) are the same thing: a system developed by General Motors that deactivates cylinders during periods of low engine load. It was used on certain 5.3L, 6.0L, and 6.2L engines starting in 2005 and continued until the release of late-model direct-injected engines.
During periods of low engine demand, the system deactivates cylinders 1, 4, 6, and 7. The valvetrain for these cylinders includes special lifters, and when the system is activated, solenoids positioned on the underside of the engine valley shut off pressurized oil via special passages to these lifters. This causes the lifter to collapse, allowing the body of the lifter to continue moving up and down with the lobes of the camshaft while the plunger that engages the pushrod remains stationary. Since the pushrods are not engaged, the valves for the DOD cylinders remain closed. The ECM turns off the injectors for these cylinders at the same time. When the system shuts off, the solenoids close, the lifters pump back up, and normal operation resumes.
While it’s an interesting system, it brings a variety of problems. The biggest one is that the system is highly susceptible to carbon contamination. There’s also the issue that while the DOD system is activated, the internals of the lifters have only the oil that happened to be there when the system activated for lubrication. As one can imagine, this is hard on the lifters and the engine oil. These systems seem to survive if the engine is well maintained and the oil is changed religiously, but someone with a casual attitude about oil changes or using the wrong oil viscosity can wreak all kinds of havoc. Higher-mileage engines have an even higher likelihood of failure. The most common complaint is valvetrain noise, but misfiring (which is what our engine was doing) and even serious internal engine damage have been traced to this system. While AFM is said to improve mileage by 5-7 percent, in the eyes of most enthusiasts the drawbacks cancel out any advantages.
The good news is that it’s possible to eliminate all traces of DOD/AFM, but the bad news is that it requires internal engine work. Deleting the DOD system the right way involves pulling the heads and installing a new camshaft and lifters, a new engine valley cover, and much more.
