Air Injection: Description and Operation

Air Injection System (AIS):

This type air injection system is commonly known as a "Pulse Air Injection". The system is designed to reduce hydrocarbon (HC) and carbon monoxide (CO) emissions by supplying fresh filtered air, through the reed valves, into the exhaust manifold and exhaust pipe. When this air meets the hot exhaust gases inside the manifold, combustion continues, further oxidizing the HC and CO in the exhaust. These pollutants are then converted into carbon dioxide and water vapor. After cold start-up, and during periods of engine warm-up the additional heat energy released helps to bring the catalyst up to operating temperature more quickly.

The system consists of: ACV solenoid valve, air control valves, reed valves, coolant temperature sensor, idle switch, and the engine control unit (ECU).



REED VALVES
Pulse air injection uses reed valves in the air cleaner housing to permit air to be drawn into the exhaust when manifold pressure is below atmospheric, while preventing exhaust gas from escaping through the system when manifold pressure is greater than atmospheric.

Reed valve "A" supplies secondary air into the exhaust manifold when the No. 1 or No. 2 air control valve passage opens, and when both are open.

Reed valves "B" and "C" supply secondary air into the exhaust pipe just downstream of the front catalytic converter.


ACV SOLENOID VALVE
The ACV solenoid valve applies vacuum to the No. 2 air control valve according to a signal from the emission control unit.

AIR CONTROL VALVES
No. 1 air control valve supplies secondary air to reed valve "A" according to intake manifold vacuum.

No. 2 air control valve supplies secondary air to reed valve "A" when the ACV solenoid is on.

REED VALVES
Reed valve "A" supplies secondary air to the exhaust manifold. Reed valves "B" and "C" supply secondary air to the exhaust pipe just behind the front catalytic converter.

ENGINE CONTROL UNIT (ECU)
The ECU monitors engine operating conditions through various sensors and controls vacuum solenoid valves that regulate AIS operation.