Air Injection: Description and Operation

Secondary Air Injection System:

PURPOSE
The system is designed to reduce hydrocarbon (HC) and carbon monoxide (CO) emissions by supplying fresh air to the exhaust ports and main catalytic converter.

OPERATION
When system air meets exhaust gases exiting the combustion chambers, combustion continues, further oxidizing HC and CO. After cold start-up, and during warm-up, additional heat released brings the catalyst up to operating temperature more quickly. When the car is being driven in high gear, the air control valve directs some air downstream promote oxidation in the main catalytic converter. The system consists of an air pump, check valve, air control valve, three way solenoid valves, and the ECU.

Air Pump
Pump is belt driven with a magnetic clutch. ECU engages and disengages clutch under various operating conditions through the air pump relay.

Check Valves
There are two system check valves. One is located in the air line going to the exhaust ports and the other is located in the air line going to the catalytic converter. Check valves allow pump air delivery while preventing exhaust gases from backfeeding and damaging system components.

Relief Valve
When open by vacuum directed through solenoid relief valves, relief valve exhausts air pump output to atmosphere rather than to exhaust port or catalytic converter.

Air Control Valve
Directs air to either the exhaust port, main converter, or relief air silencer.

Solenoid Switching Valve
Solenoid switching valve controls operation of switching valve section of air control valve.

Solenoid Relief Valves 1 and 2
Relief valves control operation of relief valve section of air control valve.

Split Air Bypass Solenoid Valve
Split air solenoid valve is a part of the air control valve. It controls amount of air allowed to flow to the catalytic converter.

Port Air Bypass Solenoid Valve
Port air solenoid valve diverts a measured quantity of air to the exhaust manifold under certain conditions.

Mileage Switch
Because of unique problems (such as oil injection) associated with controlling rotary engine emissions, Mazda incorporates a secondary air injection system with performance characteristics that vary with vehicle mileage. With switch input, the ECU compensates for engine condition changes by altering distribution of secondary air in a manner designed to both reduce emissions and extend service life of components such as catalytic converters and oxygen sensor. Switch is "OFF" below 20,000 miles (34,000 km), and "ON" above. When switch is "OFF," ECU signal at terminal 1N is below 1.5V. When switch is "ON," signal is battery voltage.