Diplomat V8-318 5.2L VIN K 2-bbl (1982)
Vacuum Restrictor: Description and Operation
PURPOSE
The Orifice Spark Advance Control Valve (OSAC) valve reduces the emission of Oxides of Nitrogen (NOx).
OPERATION
The valve controls the vacuum to the vacuum advance actuator of the distributor. A tiny orifice is incorporated in the OSAC valve which delays
the change in ported vacuum to the distributor by about 17 seconds (10 or 27 seconds on some applications) when going from idle to part throttle.
When going from part throttle to idle, the change in ported vacuum is instantaneous. On 1973 models, the valve will only delay the ported vacuum
signal when the ambient temperature is approximately 60° F. or higher.
Vacuum is obtained by a vacuum tap just above the throttle plates of the carburetor. This type of tap provides no vacuum at idle, but provides
manifold vacuum as soon as the throttle plates are opened slightly. Proper operation of this valve depends on air tight fittings and hoses and
freedom from sticking or plugging due to deposits.
