Air Injection: Description and Operation

Secondary Air Injection System:

Air System:

PURPOSE
The Secondary Air Injection (AIR) system helps reduce Hydrocarbon (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx) exhaust emissions. It also heats up the warm up 3-way catalytic converters quickly on engine start-up so conversion of exhaust gases can occur sooner.

SYSTEM COMPONENTS
AIR Pump
The AIR pump supplies the air to the AIR system. The electric air pump pressurizes air from the engine air cleaner and pumps it to the check valves near the exhaust manifolds.

AIR Pump Operation
The AIR pump is controlled by the Powertrain Control Module (PCM). Battery voltage to the AIR pump is controlled by the AIR pump relay. An integral stop valve prevents air flow through the pump during "OFF" periods. When the PCM provides a ground circuit for the secondary AIR pump relay, battery voltage is allowed to power up the AIR pump and integral stop valve. The AIR pump motor is protected by a 25 amp fuse and has its own remote ground.

Check Valves
The check valves prevent back flow of exhaust gases into the pump in the event of an exhaust backfire.

Plumbing
This system is equipped with the following components:
^ Air hose to check valve
^ Air crossunder pipe
^ Air hose to air cleaner assembly
^ Air hose to crossunder pipe
^ Vacuum bleed valve

Vacuum Bleed Valve
This valve, along with turning the AIR pump "ON" during cranking, helps prevent vacuum buildup within the AIR system, which could prevent the integral stop valve from opening.

OPERATION
AIR Pump Control
The AIR pump with integral stop valve is controlled by the PCM. The PCM will turn "ON" the AIR pump by providing the ground to complete the circuit which energizes the AIR pump relay. When air to the exhaust ports is desired, the PCM turns "ON" both the integral stop valve and AIR pump.

The PCM turns "ON" the AIR pump after start-up any time engine coolant temperature is above -8.5°C (17°F). The AIR pump will operate for a maximum of 240 seconds, or until the system enters "Closed Loop" operation. At the same time the PCM turns the AIR pump "OFF," it also de-energizes the integral stop valve solenoid so no air is directed to the exhaust ports.

SYSTEM DISABLE CONDITIONS
The AIR system will be disabled under the following conditions:

^ When the PCM recognizes a problem and sets a diagnostic trouble code.
^ When the fuel system is operating in "Closed Loop."
^ The AIR pump has been "ON" for 240 seconds.
^ RPM is greater than 2825.
^ Manifold Absolute Pressure (MAP) is greater than 96 kPa (14 psi) with Vehicle Speed Sensor (VSS) over 60 mph.
^ MAP is less than 20 kPa (3 psi).
^ Engine Coolant Temperature (ECT) less than -8.5°C (17°F).
^ Warm up 3-way catalytic converters over temperature detected.
^ Short and long term fuel trim are not in their normal ranges.
^ Engine RPM below 400 RPM.
^ Power enrichment is detected.

RESULTS OF INCORRECT OPERATION
No Air Flow
If no air (oxygen) flow enters the exhaust stream at the exhaust ports, HC and CO emission levels will be too high.

Constant Air Supply
Air flowing to the exhaust ports at all times could increase temperature of the warm up 3-way catalytic converters.