Mixture Control System

Mixture Control System Description
The anti-afterburn valve senses intake manifold vacuum change during gear shifting or deceleration, and supplies fresh air into the intake manifold in order to prevent the escape of unburned fuel.

Operation
When manifold vacuum suddenly increases, such as, during deceleration, the diaphragm in the valve unit moves, opening the valve. Air flow from the air chamber to the sensing chamber is restricted by an orifice, creating a pressure differential on the diaphragm, which holds the valve open. This unbalanced condition lasts for a few seconds until the pressure in both chambers is equalized by air entering through the orifice, then the spring pushes the diaphragm up, closing the valve.

The anti-afterburn control solenoid valve is provided to control the operation of the anti-afterburn valve by introducing manifold vacuum to the anti-afterburn valve diaphragm holding the valve closed. When the engine coolant temperature is below the set temperature of the thermosensor, and vehicle speed (only for M/T) is below the preset value of the [1][2]control unit or the shift lever position switch (only for A/T) is at the Neutral or Park position, the anti-afterburn control solenoid valve is activated to open the vacuum passage. When the anti-afterburn control solenoid valve opens, the anti-afterburn valve does not open because there is no vacuum difference on the diaphragm.