GM keeps controversial cylinder deactivation system

General Motors’ new V8 trucks will continue to feature Dynamic Fuel Management (DFM), a system that has been polarizing among truck buyers. DFM operates by monitoring load and throttle inputs to run the engine on as few as two cylinders or as many as all eight, automatically shutting down individual cylinders during light cruising or low-speed operation.

The system has 17 distinct firing patterns and is designed to maximize fuel economy. However, some owners have voiced long-term reliability concerns over the system’s mechanical and electronic complexity, particularly with regards to collapse-prone valve lifters and associated pushrod wear.

The ECU uses electronic solenoids in the Valve Lifter Oil Manifold to route engine oil pressure into specialized, collapsible lifters. When oil pressure enters a DFM lifter, it unlatches internal locking pins, causing the inner core of the lifter to collapse and the intake/exhaust valves to stay closed.

This process can lead to rapid deterioration of the mechanical components, as the specialized lifters constantly engage and disengage their internal locking pins thousands of times per trip. The internal pins or springs can get stuck due to debris, sludge, or low oil pressure, causing the lifter to fail to re-engage or stick closed at the wrong time.

If a DFM lifter collapses permanently or stops rotating on its roller, it can grind against the camshaft lobe, ruining the cam lobe and potentially creating metal shavings that circulate through the engine oil. These concerns have generated bad feelings from prospective shoppers hoping for a back-to-basics approach after the numerous issues faced by GM’s fifth-gen small-block V8s.

General Motors’ decision to keep DFM, along with the removal of a traditional engine oil dipstick and replacement with electronic oil monitoring sensors, has been met with criticism. The new 6.6-liter L78 engine claims the title of the most powerful naturally aspirated V8 in the light-duty pickup segment, with 481 horsepower and 501 lb-ft of torque.

A General Motors representative noted that the company sold 593,065 light-duty trucks in 2025, including 362,909 Silverado 1500s and 230,156 GMC Sierra 1500s. If Dynamic Fuel Management were a feature that ‘no one likes,’ it would be difficult to reconcile that characterization with the continued success of these trucks at retail.

Whether the new Gen 6 engines can deliver long-term durability remains to be seen—especially as GM continues to manage the fallout and recalls surrounding the outgoing 6.2-liter V8.