Cold Lock-Out Spark System: Operation

When engine coolant is below 128°F, PVS is closed and manifold vacuum passes through the restrictor to the distributor vacuum advance. When heavy acceleration is applied, manifold vacuum is bled off slowly through the restrictor. This avoids a sudden ignition timing retard on cold engine acceleration. When engine coolant temperature is above 128°F, PVS opens allowing vacuum to flow unrestricted.