System Purpose and Operation
The secondary air injection system is an aid to reducing levels of pollutants in the exhaust gases. It does this by
introducing a small amount of air into each exhaust port as the exhaust valve opens. The introduced air helps
promote further combustion of the fuel mixture in the exhaust system
after it has left the combustion chamber.
At certain specific engine speeds above idle (determined by the factory programming of engine management
system), the secondary air injection control valve is opened by the ECM and allows an air feed into the secondary
air system where, each time a pair of exhaust valves open, the exhaust gases in the exhaust port create a
depression which causes reed valves in the secondary air injection system to open. When open, the depression
in the exhaust port draws air from the control valve, through the open reed valves, into the exhaust port. This air
promotes secondary combustion of the exhaust gases in the ports and the header system.
At other engine speeds, the system is disabled by closing the control valve in the system. This allows an oxygen
sensor to control air to fuel ratios. If air was fed to the exhaust system when the oxygen sensor was operational,
the incoming air would cause inaccuracies in the readings sensed by the oxygen sensor (which requires access
to 'raw' combustion gases) which would lead to rough running.
Service
Manual
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Speed Triple
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