Sub Systems

Fig. 46 - EGR Cold Start Cycle System:

The EGR/CSC (Cold Start Cycle) System, used on some vehicles, regulates both distributor advance and EGR valve operation according to coolant temperature by sequentially switching vacuum signals. The major system components are, a 95° F EGR-PVS (Ported Vacuum Switch) valve, a SDV (Spark Delay Valve) and a vacuum check valve, Fig. 46.

When engine coolant temperature is below 52° F, the EGR-PVS valve admits carburetor EGR port vacuum (at about 2500 RPM) directly to the distributor advance diaphragm, through the one way check valve. At the same time, the EGR-PVS valve shuts off carburetor EGR vacuum to the EGR valve and transmission diaphragm.

When engine coolant temperature is 95° F and above, the EGR-PVS valve is actuated and directs carburetor EGR vacuum to the EGR valve and transmission diaphragm instead of the distributor. At temperatures between 82° and 95° F, the EGR-PVS valve may be open, closed or in mid position.

The Spark Delay Valve delays carburetor vacuum to the distributor advance by restricting the vacuum signal through the SDV for a predetermined time. During normal acceleration, little or no vacuum is admitted to the distributor advance diaphragm until acceleration is completed and engine coolant temperature is 95° F or higher.

The check valve blocks off vacuum signal from the SDV to the EGR-PVS valve so that carburetor spark vacuum will not be dissipated when the EGR-PVS valve is actuated above 95° F.

The 235° F PVS valve which is not part of the EGR-PVS system is connected to the distributor vacuum advance to prevent engine overheating while idling.