Air Injection: Description and Operation

Fig. 12 Thermactor Air System:

Fig. 13 Bypass/diverter valve:

Fig. 14 Dual Air Control Solenoids:

The efficiency of the catalytic converter is dependent on the temperature and chemical composition of the exhaust gases. To meet these requirements, the Thermactor System is used. This system consists of the following components.
1. Air Supply Pump
2. Thermactor Bypass/Diverter Valve
3. Dual Thermactor Air Control Solenoids
4. Exhaust Check Valve
5. Three-Way Catalytic Converter (TWC/COC).
Since air must be provided to the COC catalyst for the oxidation of HC and CO by-products of the TWC catalyst, the air supply pump provides the source of the air controlled by the bypass/diverter valve as determined by the ECA.
The thermactor air has three possible routings through the bypass/diverter valve, Fig. 12. Downstream air is the air injected into the three-way catalyst between the reduction and oxidation catalyst. Upstream air is the air injected into the exhaust manifold. Bypass air is the air bypassed to atmosphere.
The appropriate routing for thermactor air is determined by the ECA based on the engine coolant temperature versus time curve and other sensor parameters. The actual values are according to calibration. During normal coolant temperature operation the thermactor air is normally directed downstream. This downstream mode can be modified by sensor inputs to the ECA. The thermactor air is bypassed when time at closed throttle exceeds a set time value. Thermactor air will also be bypassed if the time between the EGO lean/rich sensor exceeds a set time value. The above mentioned time values are for catalyst damage prevention and/or vehicle safety. The thermactor air will also be bypassed during wide open throttle or during extended closed throttle operation. During warm-up the thermactor air will be directed upstream. This is to remove excessive amounts of HC and CO produced during the warm-up period. The bypass/diverter valve is operated by controlling vacuum from the intake manifold vacuum reservoir.
The bypass/diverter valve, Fig. 13, operation is controlled by two solenoid valves. The valves are mounted on the righthand fender apron. The solenoid closest to the rear is a diverter solenoid, while the forward solenoid is a bypass solenoid, Fig. 14.
The check valve allows thermactor air to enter the exhaust port and converter, but prevents the reverse flow of exhaust gases in the event of improper operation of system components. A valve is located between the bypass diverter valve and the exhaust port and between the catalytic converter and bypass/diverter valve.