Air Injection: Description and Operation

Description:

DESCRIPTION
The Air Pump System helps reduce hydrocarbon (HC), carbon monoxide (CO) and oxides of nitrogen (NOx) exhaust emissions. By heating up the catalytic converters quickly on engine start-up so conversion of exhaust gasses can occur sooner. The air pump consists of the air pump, combination valve, air pump solenoid, air pipe and hoses, and the check valve.

OPERATION
The air pump is a turbine type which is permanently lubricated and requires no periodic maintenance. The air pump is controlled by the PCM. When air is required in the exhaust manifold, the PCM will command the air pump On. The PCM will turn the air pump On by providing a ground, completing the circuit which energizes the air pump relay. The combination valve is controlled by the air pump solenoid and will be energized shortly after the air pump is commanded On.

The air pump solenoid also helps to prevent vacuum buildup within the air pump system. An air pump solenoid which is not functioning properly could prevent the combination valve from opening. This may result in no air flow to the exhaust manifold or delay the delivery of air, which may cause a diagnostic to fail.

Air in the engine compartment enters the air pump system through the air inlet port on the air pump. The pump filters and pressurizes the air. The pressurized air travels to the combination valve through the air hose.

The throttle body induces vacuum in the vacuum line which is regulated by the air pump solenoid. The air pump solenoid is attached to the combination valve through a vacuum hose. The PCM energizes the solenoid, opening a path to the spring-loaded diaphragm (upper valve) within the combination valve. Vacuum draws the upper valve open (up), allowing air to pass through toward the reed valve (lower valve) Air pressure forces the lower valve open, allowing air to flow to the exhaust manifold through the stainless air pipe.


The PCM monitors the following to control the Air System:
^ Engine coolant temperature (ECT) sensor
^ Manifold air temperature (MAT) sensor
^ Manifold absolute pressure (MAP) sensor
^ Airflow
^ Front oxygen (O2S) sensor

The air pump operates at 200 L/min at a nominal voltage and current of 13.5 volts and 12 amps, respectively. The air pump will operate for a maximum of 60 seconds. Before the PCM turns the air pump off, it de-energizes the air pump solenoid so that no air is directed back into the air pump's exhaust port. The reed valve prevents back flow of exhaust gases into the air pump in the event of an exhaust backfire.

DIAGNOSTIC AIDS
The air pump system will be disabled under the following conditions:
^ The PCM recognizes a problem and sets a diagnostic trouble code.
^ The fuel system is operating in Closed Loop.
^ The air pump has been On for 60 seconds.
^ Engine speed is greater than 3200 rpm.
^ MAP is less than 20 kPa.
^ Battery voltage is less than 11V
^ Air flow is greater than 30 g/s.
^ ECT is less than 4°C (40°F) or greater than 79°C (174°F)