Air Injection: Description and Operation

Secondary Air Supply System:

SECONDARY AIR SUPPLY
The Secondary Air Supply System provides additional air to the exhaust manifold. For the first 70 seconds after the engine is started and idling, the additional air helps to bring the converter up to operating temperature more quickly.
While the engine is rapidly decelerating the additional air helps the oxidation or burning reaction needed to reduce Hydrocarbons and Carbon Monoxide.
The secondary air supply system consists of an air control valve, and a control solenoid valve.
Manifold vacuum is supplied to the solenoid valve. The Solenoid valve is normally closed and vacuum is not applied to the air control valve. The solenoid valve is controlled by the FBC Unit based on engine coolant temperature, vehicle speed, and the vacuum switch which monitors manifold vacuum.
When the FBC Unit energizes the solenoid valve, vacuum is applied to the control valve. The diaphragm within the control valve is lifted against spring pressure and additional air from the air cleaner passes through a one-way reed valve. The additional air is drawn in by the negative pressure pulsations developed within the exhaust manifold. Also, the additional air is injected down-stream from the Oxygen Sensor. This is to prevent the O2 sensor from sending false readings to the Feedback Control Unit.