Exhaust Gas RECIRCULATION (EGR) System (CAPRI II): Operation
The EGR cold start cycle regulates both distributor spark advance and EGR valve operation according to coolant temperature. See Fig 1 and Fig 2. When engine coolant temperature is below 82°F (28°C), the EGR Ported Vacuum Switch (PVS) admits carburetor ported vacuum directly to distributor advance diaphragm, through one-way check valve. At the same time, the PVS shuts off carburetor EGR vacuum to EGR valve and transmission diaphragm.
When engine coolant temperature is above 95°F (35°C), the PVS is actuated and directs vacuum to EGR valve and transmission instead of distributor. At temperatures between 82-95°F (28-35°C), the PVS may be open, closed or in mid-position. The Spark Delay Valve (SDV) delays carburetor spark vacuum to distributor advance diaphragm for a predetermined time. During normal acceleration, little or no vacuum is admitted to distributor advance diaphragm until acceleration is completed.