GM's AFM And DFM Often Get Blamed For Lifter Failure, So Let's Explore How They Work

The logic behind both active fuel management (AFM) and dynamic fuel management (DFM) starts with the simple observation that most drivers "carry more engine" than they need most of the time. A V8 bought for hauling spends the bulk of its life cruising far below its performance capability, usually burning more fuel than the situation requires. GM's global chief engineer for the small block V8 program, Jordan Lee, framed the company's reasoning directly: "Rather than adding turbochargers or multi-valve cylinder heads to increase the power of smaller engines, we chose to keep the proven capability of our larger V-8 truck engines, and save fuel by switching off half of the cylinders when they aren't needed (via GM Authority)."

Both systems rely on specialized hydraulic lifters and an oil-pressure control system built into the engine's valley. With AFM, eight of the sixteen lifters are collapsible, capable of deactivating four predetermined cylinders — often cylinders 1, 4, 6, and 7 on a V8. Solenoids built into the valley plate divert oil pressure to control ports on these lifters. When commanded to deactivate, the lifters collapse, the valves on those cylinders stay shut, and fuel injection to them cuts off entirely. The pistons keep moving, but they do nothing — no air in, no fuel burned, and no power produced.

DFM, which debuted on GM's second-generation EcoTec3 engines for the 2019 model year, took the same fundamental approach and made it dramatically more flexible. Instead of designated lifters being either active or AFM-collapsible, every lifter in a DFM engine can deactivate independently. A dedicated controller monitors accelerator pedal position 80 times per second and calculates exactly how many cylinders are needed to deliver the required torque, enabling the engine to run in 17 distinct cylinder patterns rather than simply toggling between V8 and V4 modes.

Despite the two systems keeping V8s practical in an era where fuel efficiency is king, there have been some questions as to whether AFM can cause engine damage and mechanical complications that hinder its greatness. Both systems are blamed for stuck lifters, ticking noises, and expensive cam repairs across GM's V6 and V8 engines.

As mileage accumulates, AFM lifters have a documented history of sticking or failing to either collapse or re-latch properly. When a lifter fails to unlock or relatch, that cylinder's valves stop operating entirely — usually announced first by a ticking or tapping noise from the valvetrain, particularly at idle, before escalating into misfires and a check engine light. Left undiagnosed, a stuck lifter can grind down the camshaft lobe, turning what started as a single bad lifter into a full camshaft replacement.

The AFM and DFM systems aren't failing because the underlying idea is flawed. Running fewer cylinders under light load genuinely does save fuel, with EPA's testing showing 5% to 7% fuel economy improvements in ideal conditions. But asking sixteen small mechanical parts to repeatedly collapse and relatch thousands of times a day, for years, may be too much.