Exhaust Gas Recirculation: Description and Operation

Fig. 36 Egr Valve:

The EGR system introduces small amounts of exhaust gas into the intake stream during part-throttle engine operation. Exhaust gasses dilute the incoming air/fuel charge, lowering combustion temperatures and limiting formation of nitrogen oxides (NOx). Depending on year and model, the systems consist of either one or two EGR valves, Fig. 36, an electrical, mechanical, or vacuum control system, and a network of tubing to transfer exhaust gasses. All models use a filter to remove coarse impurities from the exhaust gas.