Orifice Spark Advance Control: Description

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Orifice Spark Advance Control (OSAC) valve is used on some engines to assist in control of NOx emissions. System controls vacuum to vacuum advance actuator of the distributor. A tiny orifice in OSAC valve delays changes in vacuum to distributor by about 10-27 seconds (depending on application), when going from idle to part throttle. When going from part throttle to idle, vacuum change is instantaneous.

Fig 1: Typical OSAC Valve Vacuum Hose Routing

Courtesy of CHRYSLER GROUP, LLC

NOTE: For vacuum hose routings on all engines, see CHRYSLER CORP. VACUUM DIAGRAMS in this section.