Automakers have gotten craftier over the years in terms of improving their vehicles’ fuel economy. While some have resorted to producing fully electric vehicles, others have integrated cylinder deactivation systems into their lineups.
What Is Cylinder Deactivation?
Cylinder deactivation is a feature found in many multi-cylinder engines that lets the powertrain control module (PCM) disable a number of cylinders during low-load conditions.
With a cylinder deactivation system, some engines can operate on four of eight cylinders or three of six cylinders. This system can help reduce an engine’s displacement and improve fuel economy.
Cadillac first introduced cylinder deactivation technology in 1981 with the Cadillac L62 “V8-6-4” engine but this early technology proved to be very unreliable, primarily because the computers during that era of automotive history weren’t capable of processing data quickly enough for it to work right.
But due to mechanical issues with present-day cylinder deactivation systems, some remanufacturers that build engines for today’s vehicles offer the option of buying a replacement engine with the cylinder deactivation feature deleted specifically due to reliability issues.
Early Ford Triton engines deactivate cylinders when the engine gets too hot. They monitor cylinder head temperature and, in an overheating situation, the PCM kills every other cylinder without changing valve operation so the deactivated cylinders can pump air to help keep the engine cool. This isn’t to save fuel; it saves the engine.
By alternating the active cylinders, the engine can continue to operate safely but with reduced power, to allow the driver to reach a service location or stop safely.
How Does a Cylinder Deactivation System Work?
On today’s platforms, the PCM monitors engine speed, coolant temperature, throttle position, and engine load to determine the right time to deactivate the cylinders. Two-stage hydraulic valve lifters also play an important role in deactivating the cylinders.
Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.
Pro Tip: One method used on Asian cars is a moveable pin that deactivates the intake and exhaust valves in the deactivated cylinder. When a cylinder is deactivated, fuel isn’t delivered to that cylinder for obvious reasons.
Once the engine computer determines that a cylinder can be deactivated, oil passes through a passage in the valve lifters, depressing the pin and letting the outer portion of the lifter follow the contour of the cam.
Meanwhile, the inner portion stays in place and keeps the valve closed. The lifter oil manifold has solenoids that control the oil flow, which can activate or deactivate the cylinders.
Other systems use a pump lobe and “master cylinder” on the exhaust camshaft that provides oil pressure to the lifter and an accumulator along with a solenoid to vent lifter pressure when the cylinder is deactivated. There are several methods used.
Early Cylinder Deactivation Systems
On the early ‘80s Cadillac platform, when the system determined that cylinder activation was permissible (highway cruise), it locked the rocker arms with special solenoids and this prevented the camshaft from operating the valves in the cylinders that were not needed.
The air trapped in the deactivated cylinders acted as a cushion to smooth out the engine operation and reduce any misfiring sensations.
What Happens When the Cylinders Are Working?
The concept of cylinder deactivation can be quite hard to imagine given that there are a lot of parts involved. To further understand this feature, let’s discuss what normally happens when all cylinders are working.
When all cylinders are activated, the driver controls the airflow with the throttle body. At the same time, this airflow needs to be restricted to prevent generating too much torque under light loads.
By restricting the airflow, a loss in overall pumping efficiency is to be expected.
Light loads will cause the engine to deactivate some cylinders. By this time, the relative flow to the remaining active cylinders should increase. For this to happen, the throttle should open slightly and increase the intake manifold absolute pressure.
By drawing in less vacuum across the throttle blade than usual, some of the pumping losses are freed up, improving fuel economy.
Total available torque is limited whenever some cylinders have been deactivated. Should the driver need any more torque than the minimum, only then will the engine activate all the cylinders.
Cylinder Deactivation In Diesel Engines
Exhaust heating is the primary purpose of cylinder deactivation in diesel engines.
Deactivating cylinders during low loads will cause the active cylinders to work harder and produce more heat. As a result, the aftertreatment system will get hotter at a faster rate, which reduces exhaust emissions in the process.
In diesel engines, deactivating cylinders during low-load operation can also result in active diesel particulate (DPF) regeneration without dosing the diesel oxidation catalyst.
Is Cylinder Deactivation Bad?
Engines can benefit greatly from cylinder deactivation.
When paired with early or late intake valve closing technology, cylinder deactivation can help reduce fuel consumption by approximately five to 25% while maintaining high operating temperatures at low load conditions.
Another benefit of cylinder deactivation technology is that it can help reduce harmful exhaust emissions from vehicles, particularly nitrogen oxides (NOx).
Over the years, automakers have been making conscious efforts to produce greener vehicles, and cylinder deactivation technology has proven to be a step in the right direction.
Lastly, cylinder deactivation makes the remaining active cylinders more thermodynamically efficient, which can reduce mass airflow.
Reduced mass airflow also reduces the pumping effort to move air, producing a lower-than-normal air-fuel ratio in the process.
Manufacturer-Specific Cylinder Deactivation Systems
Several automakers have adopted the concept of cylinder deactivation systems, integrating the technology into their own models.
Active Fuel Management
Formerly known as Displacement on Demand (DOD), General Motors’ (GM) Active Fuel Management technology is the American automaker’s own version of cylinder deactivation.
Active Fuel Management aims to increase fuel economy without compromising engine performance or resorting to a smaller force-inducted powertrain.
GM vehicles with Active Fuel Management use hydraulic valves and sophisticated software to shut off cylinders when limited power is needed. The solenoid system then collapses the valve lifters to reduce pumping losses.
Active Fuel Management isn’t limited to vehicles with this built-in feature. Drivers can opt to add this tech to their own vehicles with a few requirements, including the following:
- Special valve lifters
- Lifter oil
- Manifold assembly
- Advanced engine control module
Multiple Displacement System
Multiple Displacement System (MDS) is Chrysler’s take on the cylinder deactivation technology. The fuel-saving feature can help improve fuel economy by as much as 20%.
Cylinder deactivation isn’t new for Chrysler. In fact, the automaker was the first to launch the tech in an SUV when it debuted the 2005 HEMI-powered Jeep Grand Cherokee.
Chrysler’s MDS is standard on the following vehicles:
- Chrysler 300C
- Dodge Magnum R/T
- Dodge Charger R/T
- HEMI-powered Dodge Durango
- Dodge Ram 1500
- Jeep Grand Cherokee
- Jeep Commander
In 2005, Executive Vice President for Product Development Eric Ridenour predicted that by 2007, Chrysler would have sold nearly one million vehicles with Multiple Displacement System technology.
It was also predicted that 60 million gallons of fuel would have been saved annually with the fuel-efficient feature.
Key Takeaways
Cylinder deactivation systems have been around for quite some time, with automakers having their own terms for the tech. General Motors calls it Active Fuel Management, while Chrysler calls it Multiple Displacement System.
Regardless of the term, cylinder deactivation aims to improve fuel economy without compromising engine performance or downsizing the powertrain. Engine speed, coolant temperature, throttle position, and engine load are some of the things the PCM needs to monitor to determine the right time to deactivate the cylinders.
In most cases, the PCM deactivates four of eight cylinders or three of six cylinders under low-load conditions. Aside from improving fuel economy, cylinder deactivation can also help reduce NOx emissions and active DPF regeneration.
Get High-Quality Cylinder Heads and Gaskets
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