Pic. 2-92. Diagram of the exhaust gas recirculation system:
1 - carburetor; 2 - thermal vacuum switch of the recirculation valve; 3 - inlet pipe; 4 - exhaust manifold; 5 - recirculation valve; 6 - recirculation tube.
When the engine coolant temperature is above 40-48°C, the thermal vacuum switch is activated, vacuum is applied to the recirculation valve, the valve opens, part of the exhaust gases from the exhaust manifold 4 is sucked into the intake pipe and the engine.
Checking the performance of the exhaust gas recirculation system
Press the carburetor throttle actuator lever and gradually increase the engine speed to 2500-3000 min-1. At a coolant temperature of 30-38°C, the recirculation valve 5 must be closed, and at a liquid temperature of 40-48°C, it must be open, as can be seen from the rise of the recirculation valve stem. If the recirculation valve does not open, check the valve and thermal vacuum switch 2.
To check, disconnect the recirculation valve from the thermal vacuum switch and apply vacuum using a manual vacuum pump to the diaphragm cavity of the valve. At a vacuum of 9.3 kPa (70-75 mmHg Art.) valve must be closed. At a vacuum of more than 59.9 kPa (450-455 mmHg Art.) the valve must be fully open, which is checked by a sharp removal of vacuum, the valve will close with a sharp click. Air leakage in both modes is not allowed within 5 s.
When checking the thermal vacuum switch 2, disconnect the hose from it and the recirculation valve 5. Use a manual vacuum pump to apply a vacuum of 13.3 kPa (100±5 mmHg Art.) to the thermal switch. At a coolant temperature of not more than 30-38°C, vacuum leakage is not allowed (thermal vacuum switch closed). At a liquid temperature of less than 40-48°C, vacuum should not be created (thermal vacuum switch open).