Air Injection System and Smog Pump Operation

The air injection system (AIS) is designed to introduce clean air to the engine exhaust as it exits the exhaust manifold or exhaust headers. Exhaust gases are at their hottest as they leave the combustion chambers. Introducing oxygen to the exhaust at this point allows continued burning of the fuel mixture as it travels down the exhaust system and ultimately out the tailpipe.

Air injection systems consist of mainly two different designs. Your vehicle's Underhood Emissions Label can provide you with information regarding the requirements of this emission system design and equipped components.

Pump Type: The first system known as the Pump Type includes an air pump, commonly known as the smog pump, which is responsible for supplying fresh pressurized oxygen to the exhaust stream through header or exhaust manifold, and/or before the Catalytic Converter. The components of this system are the air pump, the diverter valve, the air distribution manifold; both known as exhaust manifold and exhaust headers, and the air check valve.

Pulse Type: The second type of system known as the Pulse Air System is much simpler and only relies on the vacuum created in the exhaust stream as it travels down the exhaust manifold and passages. As the engine cycles, this vacuum draws fresh oxygen into the Air Injection lines. The air is then used to prolong thorough exhaust burning. This system should consist of a metal duct or hose approximately 1" in diameter around the air cleaner leading to a metal air check valve, and then the exhaust manifold.

Operation: Pump Type - The spinning vanes of the air pump force air into the diverter valve. During acceleration air is forced through the diverter valve, the check valve, the air injection manifold, and into the exhaust stream. During deceleration the diverter valve blocks air flow, preventing a backfire that could damage the exhaust system. When needed, the diverter valve will release excess pressure to the air cleaner.

Pulse Type - As exhaust gases travel down the exhaust passages, the vacuum created draw fresh oxygen into the air injection system. Fresh air then travels through the diverter valve, check valve and to the exhaust manifold.

For the Smog Test: During the visual inspection portion of the smog test the smog technician will be inspecting your vehicle's air injection system. If your vehicle is equipped with a pump air injection system the technician will be checking for the proper connection of the injection system plumbing, all hoses, lines, valves and smog pump.

The smog technician will also examine the air pump belt for proper tension and damage. During your at-home check up ensure all connections are intact and components present. If it appears there are missing parts or open ends seek repair assistance from a certified smog repair station before subjecting your vehicle to the smog inspection.

For vehicles equipped with the pulse air injection system, the technician will only inspect the injection pipes and valves.

Note: During the smog test the air injection system is only visual inspected. The smog technician will not ensure the proper operation of this system, rather he or she will only verify that the system is installed and properly connected.


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