New GM V8 Trucks Keep Controversial Cylinder Deactivation

We know General Motors is introducing two brand-new naturally aspirated Gen 6 Small Block V8 engines for the 2027 Chevrolet Silverado 1500 and 2027 GMC Sierra 1500.

While both new small-block V8s deliver significant performance gains over the outgoing engines, they also retain a controversial piece of fuel-saving hardware that has long frustrated owners and forum users. Both the new 5.7-liter V8 (L76) and 6.6-liter V8 (L78) will continue to use GM’s Dynamic Fuel Management (DFM) system.

First introduced on the 2019 model year half-ton trucks, DFM operates as the follow-up to GM’s older Active Fuel Management (AFM).

Unlike the old system, which simply turned off half the cylinders, DFM uses the ECU to monitor load and throttle inputs to run the engine on as few as two cylinders or as many as all eight. It automatically shuts down individual cylinders during light cruising or low-speed operation, and re-engages them as power demands increase. GM says the system has 17 distinct firing patterns.

But DFM is polarizing among truck buyers — some people hate the system so much they go so far as buying a DFM Disabler that plugs into the OBD-II port and permanently locks the engine into full cylinder usage. DFM adds mechanical and electronic complexity to a valvetrain that should be as simple as can be.

EDITOR'S NOTE: A previous version of this article was titled "New GM V8 Trucks Keep Controversial Cylinder Deactivation, No One Likes." It has since been revised. A General Motors representative reached out to refute that claim and included the following statement: "In 2025, General Motors sold 593,065 light-duty trucks across the Chevrolet and GMC brands, 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."

Many owners voiced long-term reliability concerns over collapse-prone valve lifters and associated pushrod wear.

Judge for yourself — this is how the system works:

• 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. This causes the inner core of the lifter to collapse, meaning the pushrod does not move, and the intake/exhaust valves stay closed.

• The system switches cylinders on and off continuously during normal driving (up to 60% of the time) to maximize fuel economy. Because the specialized lifters constantly engage and disengage their internal locking pins thousands of times per trip, the mechanical components can suffer rapid deterioration.

The Internal pins or springs can get stuck due to debris, sludge, or low oil pressure. If a lifter fails to re-engage or sticks closed at the wrong time (outside the base circle of the cam), it stops opening the valve properly. When a DFM lifter collapses permanently or stops rotating on its roller, it can grind against the camshaft lobe. This obviously ruins the cam lobe and could create metal shavings that circulate through the engine oil.

Keeping DFM — along with GM’s decision to remove a traditional engine oil dipstick and replace it with electronic oil monitoring sensors — has already 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.

With 481 horsepower and 501 lb-ft of torque, the new 6.6-liter L78 claims the title of the most powerful naturally aspirated V8 in the light-duty pickup segment, edging out the Ram 1500’s 6.4-liter V8 by 11 horsepower.

Whether these 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.

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