Bronco L6-300 4.9L VIN Y 1-bbl (1983)
Thermal Vacuum Valve: Description and Operation
Thermactor Idle Vacuum Valve (TIV)
Fig. 74 Typical Thermactor idle vacuum valve schematic
Fig. 75 Thermactor idle vacuum valve (TIV)
This valve, Fig. 74, used on some vehicles, operates in conjunction with a vacuum delay valve and provides backfire control, full time idle air dump,
cold temperature catalyst protection and cold EGR lockout. This valve prevents excessive underbody temperature caused by the exhaust system by
diverting secondary air pump output during extended engine idle.
EGR port vacuum at the carburetor moves the power diaphragm which opens or closes vents to the atmosphere by moving the valve membrane, Fig.
75. Vacuum at the EGR port switches off the thermactor at idle due to the lack of vacuum at closed throttle conditions. The idle vacuum valve is open
and dumps thermactor air to the atmosphere during cold engine operation, extended idle periods and deceleration. When the engine has reached normal
operating temperature, the vacuum valve is closed to the atmosphere to allow passage of thermactor air.
