Vacuum Piston Control System

Fig. 12 Vacuum Piston Control System:

This system allows the vacuum pistons to rise when the engine is operating under heavy load conditions.
This system consists of vacuum piston control valve, vacuum piston control solenoid valve, check valve C, and the ECU. The vacuum piston control solenoid valve is activated by the electric current from the ECU which receives the signals of the intake manifold vacuum (MAP sensor) and engine speed (ignition coil), and the intake manifold vacuum is led to the diaphragm of the vacuum piston control valve through check valve C so as to open the passage from vacuum piston upper chamber to atmosphere.
Then the vacuum piston is lowered by its own weight and the force of the return spring.