Chrysler Full-Size Vans 1967-1988 Repair Guide

Orifice Spark Advance Control

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OPERATION



See Figures 1, 2, 3, 4, 5 and 6

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Fig. Fig. 1: OSAC valve vacuum hose routing for all 1974 100 series vehicles



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Fig. Fig. 2: OSAC valve vacuum hose routing for 1975-76 light duty 100 series vehicles



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Fig. Fig. 3: OSAC valve vacuum hose routing for 1977 light duty vehicles



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Fig. Fig. 4: OSAC valve vacuum hose routing for 1979-83 inline 6-cylinder light duty vehicles



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Fig. Fig. 5: OSAC valve vacuum hose routing for 1979-83 V8 engine light duty vehicles



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Fig. Fig. 6: View of the 1979-83 OSAC valve

The OSAC system is used on light duty trucks to aid in control of nitrous oxide (NOx) emissions. The system control the vacuum signal to the distributor vacuum advance unit.

A tiny orifice is incorporated in the OSAC valve which delays the change in ported vacuum to the distributor by 17 to 27 seconds, depending on the engine and truck model, when going from idle to part throttle.

When going from part throttle to idle, the change in ported vacuum is instantaneous.

 
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