Air Injection Pump: Description and Operation

Pump Assembly:

The air pump assembly consist of a pump, mass air flow sensor (MAF), relay, bracket, and inlet filter.

The air injection system adds a controlled amount of air to the exhaust gases aiding oxidation of hydrocarbons and carbon monoxide in the exhaust stream.

The system does not interfere with the ability of the EGR system (if used) to control nitrous oxide (NOx) emissions. Turns on only during a cold start.

Air is drawn into the pump through a rubber tube that is connected to the Mass Air Flow Sensor (MAF) and filter assembly. Airflow is measured by the MAF sensor. A voltage will be produced via the MAF sensor when air is passed through. This voltage correlates to airflow. The amount of voltage (airflow) will determine the amount of fuel that will be added to achieve the goal air/fuel ratio.

Air is then compressed by the air injector pump. It is expelled from the pump and routed into a rubber tube where it reaches the air pressure relief valve. Pressure relief holes in the relief valve will prevent excess downstream pressure. If excess downstream pressure occurs at the relief valve, it will be vented into the atmosphere.

Air is then routed through a tube, through the oneway check valves and injected into the catalytic converters (referred to as downstream).

The one-way check valves protect the hoses, air pump and injection tubes from hot exhaust gases backing up into the system. Air is allowed to flow through these valves in one direction only (towards the catalytic converters).

Downstream air flow assists the oxidation process in the catalyst, but does not interfere with EGR operation (if EGR system is used).