Air Injection: Description and Operation

Fig. 72 Secondary air supply system.:

This system, Fig. 72, is designed to improve emission control performance by supplying fresh air from air cleaner into exhaust manifold through the air suction valve.
The air suction control solenoid valve is open by signals from the control unit when intake manifold vacuum is above the set value of vacuum switch C and manifold vacuum is applied to the air suction diaphragm valve to open the secondary air passage. Fresh air enters into the exhaust manifold, when negative pressure makes the air suction reed valve open.
On all models, an air bleed valve is used to prevent overheating in the exhaust system. When intake air temperature rises excessively, the air bleed valve opens and manifold vacuum, which would normally be applied to air suction diaphragm valve, is bled off. This closes the secondary air passage.