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

The logic behind each lively fuel management (AFM) and dynamic fuel management (DFM) starts with the straightforward remark that almost all drivers “carry more engine” than they need more often than not. A V8 bought for hauling spends the majority of its life cruising far below its performance capability, often burning more fuel than the situation requires. GM’s global chief engineer for the small block V8 program, Jordan Lee, framed the corporate’s reasoning directly: “Reasonably than adding turbochargers or multi-valve cylinder heads to extend the ability of smaller engines, we selected to maintain the proven capability of our larger V-8 truck engines, and save fuel by switching off half of the cylinders when they don’t seem to be needed (via GM Authority).”

Each systems depend 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, able to deactivating 4 predetermined cylinders — often cylinders 1, 4, 6, and seven on a V8. Solenoids built into the valley plate divert oil pressure to manage 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 yr, took the identical fundamental approach and made it dramatically more flexible. As an alternative of designated lifters being either lively 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 what number of cylinders are needed to deliver the required torque, enabling the engine to run in 17 distinct cylinder patterns reasonably than simply toggling between V8 and V4 modes.

Despite the 2 systems keeping V8s practical in an era where fuel efficiency is king, there have been some questions as as to if AFM may cause engine damage and mechanical complications that hinder its greatness. Each 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 — often 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 began as a single bad lifter right into a full camshaft substitute.

The AFM and DFM systems aren’t failing since 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 hundreds of times a day, for years, could also be an excessive amount of.