This recall brought to mind a question I had.

NHTSA #19V-497
Recall #3719F
ROCKER ARM CONCERN

Just curious. When cylinders are deactivated, are all the valves, kept closed, kept open, or just operate normally except with no fuel injection?

Here is recall:

Description:
On certain subject vehicles, the powertrain control module (PCM) software controlling the hydraulic valve clearance adjuster may operate improperly when transitioning from cylinder deactivation to full cylinder activation modes while driving, due to inappropriate control logic of the PCM. As a result, an intake valve rocker arm may come out of position and make contact with internal engine parts, which may cause an engine misfire and loss of power and/or Malfunction Indicator Light (MIL) illumination.
In the worst case, engine damage may occur, resulting in engine stall while driving without ability to be restarted, which may increase the risk of a crash.
Remedy:
A Mazda dealer will reprogram the PCM with improved hydraulic valve adjustment control software, so that it may operate properly when transitioning from cylinder deactivation to full cylinder activation modes while driving.

 

My understanding of all cylinder deactivation methods is that they close valves for inoperative cylinders (obviously also fuel) that is the lowest pumping loss mode with partial recovery of compression stroke on return stroke. If they were open you would have pumping losses sort of like a "Jake Brake" compression release on a Diesel. Not 100% certain however.

 

Its impossible to keep the valves closed, as they are operated by the camshaft, along with the operating cylinders.

 

Here is a nice video showing how the cylinder deactivation works and keeps valves closed on deactivated cylinders.

https://insidemazda.mazdausa.com/the...-deactivation/

 

Very interesting. I was told it was still the same old skyactiv G engine. Clearly it's a very different design for the valve train.