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Orifice Spark Advance Control: Description

Orifice Spark Advance System (OSAC) is used on most Light Duty emission models to aid in control of oxides of nitrogen (NOx). It controls vacuum to vacuum advance actuator of distributor. A tiny orifice incorporated in OSAC valve delays change in ported vacuum to distributor by about 10 seconds when going from idle to part throttle. When going from part throttle to idle, change in ported vacuum to distributor will be instantaneous.

Fig 1: Typical OSAC Valve Hose Routing (5.2L & 5.9L Engines Shown)
G09337129Courtesy of CHRYSLER GROUP, LLC
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