Caprice V8-307 5.0L (1987)
Thermal Vacuum Valve: Description and Operation
EGR Early Fuel Evaporation Thermal Vacuum Switch (EGR-EFE-TVS)
This switch controls vacuum to the EGR and EFE valves according to engine coolant temperature. This switch allows the EFE system to operate only
during engine warm-up periods, by supplying manifold vacuum to the EFE valve when coolant temperature is below the switching point. Above the
switching point, the vacuum is blocked and the EFE actuator is vented to atmosphere.
This switch also permits EGR operation at a reduced rate during warm-up and at full operation after warm-up. When engine coolant temperature is
below the switching point, vacuum is directed from the ported vacuum port to the EGR port. Above the switching point, the vent orifice is blocked so
full ported vacuum is directed to the EGR port.
