Pulsed Secondary Air Injection: Description and Operation

Fig. 69 Thermactor II system (typical):

Fig. 70 Thermactor II pulse air valve operation:

Some vehicles are equipped with this type of exhaust air injection system, Fig. 69, which does not have an air pump. The system uses the natural pulses of the exhaust system to draw air into the exhaust manifold. The system is regulated by a pulse air valve. The valve, Fig. 70, is connected to the air cleaner with a hose and to the exhaust manifold with a metal tube. Some pulse air valves closely resemble the standard Thermactor check valves, but are not interchangeable with them.

When pressure inside the exhaust manifold is more than the pressure in the air cleaner, the reed in the pulse air valve is closed. When pressure in the exhaust manifold is lower than in the air cleaner, the reed opens and allows air to be drawn into the exhaust manifold.

Fig. 71 Thermactor II pulse air valve test:

TESTING
1. Check to see that air flows freely through air cleaner or silencer to pulse air valve.
2. Check all hoses, tubes, and pulse air valves for leaks.
3. Disconnect hose at air cleaner side of pulse air valve and connect tester T75L-9487-A or equilvalent to valve, Fig. 71. A 6 inch length of hose, clamped at either end, should be used between tester and valve.
4. Squeeze bulb as flat as possible, then release it. Bulb should remain flat for at least 8 seconds. If not, valve is defective.
5. If tester is not available, disconnect hose as in Step 3 and blow air through valve toward exhaust manifold side, then attempt to suck air back through valve, the valve is defective.