Pulsed Secondary Air Injection: Description and Operation
Air Injection System
The purpose of the air injection system is to reduce HC and CO emissions during cold engine operation by supplying necessary amounts of air into the
The operating principle of the system is based on a utilization of the negative pressure caused by exhaust gas pulsation and intake manifold pressure
during valve overlap period.
The gas pressure in each exhaust port is transmitted to the air suction valve through the air suction hole and air suction pipe. When pressure transmitted
is negative, the reed valve of the air suction valve is opened towards the valve stopper and simultaneously fresh air is drawn from the air cleaner through
the air suction hose and silencer into the exhaust port. When positive pressure reaches the air suction valve, the reed is closed in an instant to prevent the
flow of exhaust gas into the valve assembly.
When the coolant temperature is below 95 deg. F, on systems using a thermoswitch and solenoid valve, the electronic control unit signals the solenoid
valve to allow manifold vacuum to open the cut-off valve(s) which is mounted within the Air Suction Valve(s)(ASV). The solenoid valve remains open
for approximately 2 minutes. At the end of 2 minutes, the control unit turns off the solenoid valve and air injection is stopped. All other systems, with no
thermoswitch or solenoid valve, operate as long as the engine is running.