Cold Start Spark Advance System: Operation

System provides intake manifold to distributor vacuum advance unit when engine coolant is above 235°F. Between 125°F and 235°F the system provides ported vacuum to advance unit through a SDV. Below 125°F, system provides ported vacuum to advance unit through an RDV. The SDV is used to delay vacuum advance when engine is at normal operating temperature. The RDV is used to hold vacuum at distributor advance for a few seconds to improve cold engine driveability. See Figure.