Firebird V8-305 5.0L (1982)
Distributor Thermal Vacuum Switch: Description and Operation
Distributor Spark Thermal Vacuum Switch (DS-TVS)
When engine coolant temperature is below the calibration temperature the switch allows no vacuum flow to the distributor.
When engine coolant temperature is above the calibration temperature, the DS-TVS allows ported vacuum to the distributor.
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The ported vacuum signal is controlled by a distributor spark vacuum delay valve (DS-VDV) which maintains vacuum advance during rapid
throttle openings, thereby improving engine response during cold engine operation.
Distributor Spark TVV
Distributor Spark Thermal Vacuum Valve (DS-TVV)
This valve supplies manifold vacuum through a distributor spark vacuum delay valve (DS-VDV) to the distributor when the carburetor air inlet
temperature is below the specified temperature. The DS-VDV maintains vacuum advance during rapid throttle opening to improve engine
response during cold engine operation. When engine coolant temperature is above the calibration temperature, ported vacuum is supplied to the
distributor through a distributor spark thermal vacuum switch (DS-TVS) with no additional vacuum controls.
NOTE: Refer to the number stamped on the base of the switch or valve for calibrated switching or activation temperatures.
Distributor Spark VRV
This valve limits the spark vacuum to a calibrated value until ported vacuum applied to the control port of the VRV is greater than the calibration
value. When ported vacuum is greater than the calibration value, full manifold vacuum signal is applied to the distributor.
Manifold and ported vacuum is applied to the VRV through two distributor spark thermal vacuum valves (DS-TVV). Ported vacuum is available
to the VRV at all times with no vacuum control. When carburetor air inlet temperature is below the specified temperature, manifold vacuum is
supplied to the VRV through a distributor spark thermal vacuum valve (DS-TVV) and controlled by an in-line distributor spark vacuum delay
valve (DSVDV). DS-VDV maintains vacuum advance during quick throttle openings, improving engine response during cold engine operation.
When engine coolant temperature is above the calibrated value of the valve, full manifold vacuum is supplied to the VRV with no additional
vacuum controls.
NOTE: Refer to the number stamped on the base of the switch or valve for calibrated switching or activation temperatures.
Distributor Spark/Canister Purge TVS
DS-CP-TVS
Valve Contains Two Separate Vacuum Circuits
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Two Upper Ports--Sealed from each other when cold and connected to each other when warm.
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Two Lower Ports--Sealed from each other when cold and connected to each other when warm
Distributor Thermal Control Valve (DTCV)
This valve is used in the manifold vacuum line to the distributor vacuum advance to improve driveability during cold engine operation.
NOTE: Refer to the number stamped on the base of the switch or valve for calibrated switching or activation temperatures.
Distributor Thermal Vacuum Switch (DTVS)
Engines With Ported Spark
This switch is used to advance the ignition timing when engine coolant temperature is high. At temperatures above the calibration value, a valve
within the TVS moves, and if not equipped with a Vacuum Reducer Valve (VRV), a full manifold vacuum is directed to the distributor vacuum
advance. On engines with a VRV, the vacuum will be 1 1/2 inches less than manifold vacuum. The timing is then advanced allowing the engine to
run cooler. This is the only time when vacuum is directed to the vacuum advance at idle.
Engines With Full Manifold Vacuum
Some engines use a DTVS to allow increased ignition timing at normal operating temperature. At temperatures above the calibration value, the
DTVS switches the vacuum supplied to the distributor from manifold vacuum to vacuum which has been reduced by 1 1/2 inches to prevent
detonation at higher operating temperatures.
Distributor Vacuum Modulator Valve (DVMV)
Distributor Vacuum Modulator Valve (DVMV)
This valve has a calibration point of 8.7 inches of vacuum. Whenever manifold or ported vacuum is less than the calibration point, the DVMV
switches to full manifold vacuum. Whenever the manifold or ported vacuum is greater than the calibration point, the DVMV switches to the
