4 Common Problems With Cylinder Deactivation

One of the more curious inventions of the automotive industry is something called cylinder deactivation. Essentially, when under light load, an engine will shut down some of its cylinders. When a driver is only placing a partial load on an engine, efficiency drops by up to 15%, according to research by engineers at the Brno University of Technology published in the journal Renewable and Sustainable Energy Reviews. This is because the amount of fuel being used just to keep the motor operating is actually greater than the amount going toward propulsion. In that situation, deactivating some cylinders will reduces the amount of fuel used and boost efficiency.

Cylinder deactivation isn’t a recent development. It actually goes back to the 1905 Sturtevant, which allowed the driver to stop half the cylinders on its V6 engine. However, the technology didn’t get much attention again until GM launched a new engine in the early 1980’s Cadillac Eldorado with what it dubbed a “V8-6-4 powerplant,” like three engines in one. Today, there are a slew of cylinder deactivation systems across the industry, including dynamic fuel management (DFM), variable cylinder management (VCM), multi-displacement system (MDS), and Camtronic, to name a few.

However, this technology can also introduce some potentially pricey problems under the hood. Some implementations have been plagued with excessive oil consumption, increased carbon deposits, vibration and noise, and lifter issues. It’s also received mixed reviews from drivers, as Hemi owners are deleting this feature, even though it’s costing them fuel. And this is hardly the only example of drivers wanting this technology out of their vehicle.

Many causes of excessive oil consumption have nothing to do with cylinder deactivation, but some drivers with the technology under their hood have reported increasingly oil-thirsty vehicles. The piston rings on some cylinder deactivation systems aren’t able to combat a partial vacuum created following the cylinders being shut down. Those stationary piston rings let oil into the combustion chamber, which can create a variety of problems, including increased oil consumption, blue smoke out of the tailpipe, and other potential performance problems.

Take Honda’s variable cylinder management ( VCM) system, which has had many drivers experiencing accelerated oil consumption. For every 1,000 miles, 1 quart of extra oil is burned up. It doesn’t help that the automaker’s response has been a little dismissive, simply recommending drivers check their oil at every fuel stop.

GM’s active fuel management (AFM) technology has also created some issues on its 5.3-liter Vortec 5300 engine. Oil was apparently sneaking past the inactive piston rings into the combustion chamber, and the issue was exacerbated by pressurized oil directed at the piston skirts from relief valves. Even worse, GM’s engines weren’t directly monitoring oil volume, so by the time other indicators revealed an issue and lit up the dashboard warning, the problem would have already been well under way.

Carbon deposit buildup can often be the reason behind a vehicle’s sudden loss of performance. These deposits essentially look like clumps or collections of black muck found around the inside of an engine, particularly near the valves and intake. According to YouTube channel TorqueCars, it can cost you up to 60% of the airways if left unaddressed.

Cylinder deactivation can increase the buildup of carbon, as the system controls the behavior of the valves. When shutting down cylinders, the valve timing must also be adjusted, potentially resulting in the intake dipping into a cylinder containing unburnt material. This exposure creates a perfect opportunity for carbon formation on the valve.

In addition, according to some reports, positive pressure is created due to certain cylinder deactivation settings. This pressure can force greater amounts of oil vapor back through the crankcase ventilation system, leaving residue on the valves that will form into carbon deposits after continuous thermal exposure.

Ideally, the cylinder deactivation technology should be virtually undetectable while driving. However, many have reported experiencing odd vibrations and strange noises, particularly when the system turns off cylinders. For instance, certain recent Mazda models have been experiencing odd sounds and shaking once drivers reached a cruising speed. These models are running a four-cylinder SkyActiv-G engine variant that still features cylinder deactivation. Meaning, once a driver reaches a consistent speed, the system goes down to just two cylinders.

According to a Mazda technical service bulletin, in order to correct the problem, it requires specially modified brackets to mount the radiator, and a fresh PCM calibration. The automaker is blaming the problem on resonance from the radiator. However, some owners are still experiencing issues when the system turns on and off the cylinders. 

If you consider that common city driving scenarios will include times full power is needed (acceleration, increasing speed to pass), and times when it’s not (cruising), the cylinders could frequently be oscillating between four and two cylinders. Vibration and noise associated with the switch back and forth, would certainly be cause for a driver to become frustrated. 

Some cylinder deactivation systems use specialized lifters to engage and disengage the cylinders. For instance, GM’s AFM system is activated by latching down select lifters via a mechanism powered by pressurized oil. When all cylinders reactivate, the oil stops flowing to the locking components on the lifters, releasing them to move freely again. This system is featured in some of the automaker’s V6 and V8 engines of years past.

Unfortunately, these small mechanical bits have been known to fail, or not function properly. The lifters that get disabled can get stuck or not relatch when the cylinder deactivation system switches on and off, which can occur countless times over the life of the engine. It may start as just an odd tapping sound, but it can escalate into full-blown failure, destroying the camshaft in the process.

In addition to misfires, other signs of failing lifters in an AFM system include, engine stalling, performance losses, and jerky idling. Some owners have attempted to head off these problems by using an AFM disabler, however that won’t be much help for those who have already begun to notice problems, it could actually make things worse.