Miscellaneous Emission Control Devices / Ignition
Ignition timing establishes when the air/fuel mixture undergoes combustion. This process is critical in controlling the emission levels produced by the engine. A variety of components have been used on vehicles before the introduction of electronic or distributorless ignition systems.
(VC) Vacuum Control devices allow the timing to be advanced or retarded under acceleration, cruise and deceleration conditions.

(DCV) Distributor Check Valves restrict the amount of vacuum acting on the vacuum control to prevent a rapid advance of ignition timing.

(KS) Knock or Detonation Sensors determine when it is necessary to retard the ignition timing to control and prevent pre-ignition.

(PVS) Ported or Thermal Vacuum Switches control the vacuum being applied to the distributor vacuum control during engine warm up.

(DSV) Spark Delay Valves prevent quick timing changes due to rapid throttle movement and they cut off spark advance during deceleration.

VC
DCV
KS
PVS
DSV