Fig. 9-15. Exhaust gas recirculation diagram: 1 - vacuum supply hose to the recirculation valve; 2 - hose for draining liquid from the carburetor heating unit; 3 - air filter; 4 - carburetor; 5 - air filter element; 6 - thermostat; 7 - engine; 8 - recirculation tube; 9 - recirculation valve; 10 - exhaust manifold; 11 - inlet pipe; 12 - thermal vacuum switch of the recirculation valve; 13 - carburetor heating unit; A - to the vacuum ignition timing regulator, B - to the coolant pump
When the engine coolant temperature is above 40-48°C, the thermal vacuum switch 12 is triggered, a vacuum is supplied to the recirculation valve 9, the valve opens, and part of the exhaust gases from the exhaust manifold 10 are sucked into the intake pipe and the engine.
Checking the functionality of the exhaust gas recirculation system
Press the carburetor throttle lever and gradually increase the engine crankshaft speed to 2500-3000 min⁻¹. At a coolant temperature of 30-38°C, the recirculation valve 9 should be closed, and at a liquid temperature of 40-48°C, it should be open, which is visible by the rise of the recirculation valve stem. If the recirculation valve does not open, check the serviceability of the valve and thermal vacuum switch 12.
To check, disconnect the recirculation valve 9 from the thermal vacuum switch 12 and apply a vacuum to the diaphragm cavity of the valve using a hand vacuum pump. At a vacuum of 9.3 kPa (70±5 mm Hg), the valve must be closed. At a vacuum of more than 59.9 kPa (450±5 mm Hg), the valve must be fully open, which is checked by abruptly removing the vacuum; the valve will close with a sharp click. Air leaks in both modes are not allowed for 5 s.
When checking the thermal vacuum switch 12, disconnect the hose from it and the recirculation valve 9. Using a hand vacuum pump, apply a vacuum of 13.3 kPa (100±5 mm Hg) to the thermal vacuum switch. At a coolant temperature of no more than 30-38°C, vacuum leaks are not allowed (thermal vacuum switch closed). At liquid temperatures below 40-48°C, a vacuum should not be created (thermal vacuum switch open).