EGR Coolant Spark Control (EGR/CSC)
At cold start, below PVS opening temperature, the ported vacuum switch connects carburetor EGR vacuum signal to the distributor through the check valve (bypassing the spark delay valve). When PVS opening temperature is reached, EGR port vacuum switches from the distributor to the EGR valve. EGR valve operation is controlled by carburetor EGR spark port and spark advance is controlled by the spark vacuum port acting through the cooling PVS and spark delay valve.