Trapped Vacuum Spark

When engine temperature is below a pre-set specified value, the manifold vacuum signal is routed through the check valve to the distributor. Ports on TVS are blocked. The check valve will keep distributor vacuum at levels higher than manifold vacuum during vehicle acceleration. A small sintered iron bleed orifice is provided in the check valve to allow for a leak-down to enable engine to be restarted if it stalls. This applies to all models except Light Duty California and Altitude Emissions, 350" and 400" V8 engines with Heavy Duty emissions and all 454" V8 engines.

When engine temperature is above pre-set value, TVS ports will be open to allow manifold vacuum to the distributor. During this mode of operation, the check valve will act as a connector and not delay or trap vacuum.