Exhaust Gas Recirculation: Description and Operation

Fig. 7 EGR valve.:

This system incorporates a vacuum operated EGR valve, which delivers a proportion of the exhaust gas into the intake system. Exhaust gas is diverted from the rear exhaust manifold and fed through the EGR valve into the rear of the intake manifold. Flow of recirculated gas varies according to engine operating conditions, and there is no recirculation at idle.
The EGR valve, Fig. 7, is controlled by a thermo vacuum valve which inhibits the EGR system until the engine warms up. This valve sends a vacuum signal to the EGR valve at opening or closing. The thermo vacuum valve opens when coolant temperature rises above approximately 109°F or closes when coolant temperature falls below approximately 91°F.