Spark Control Relay: Description and Operation

Fig. 37 - Spark Timing Control System:

This system, Fig. 37, used on 1977-78 1.8 liter, 1979-82 2.0 liter and 1981-82 2.3 liter California with manual transmission models reduces exhaust emissions by delaying vacuum to the distributor vacuum advance unit during vehicle acceleration.

The system consists of a vacuum delay valve installed in the vacuum line between the carburetor and distributor on 1.8 liter and 2.0 liter engines except California, or between the water thermo valve and distributor on 2.0 liter California engines. On 2.3 liter engines, the system consists of a spark delay valve (manual transmission equipped models) and a distributor solenoid valve installed in the vacuum line between the intake manifold and distributor. The distributor solenoid valve is controlled by a timer and water thermo switch (also a distributor water thermo switch on vehicles with automatic transmission).

The spark delay valve has an internal restrictor to slow air flow in one direction and a check valve which allows free air flow in the opposite direction.

On 1979-82 California models, distributor vacuum advance is restricted by the water thermo valve which detects engine coolant temperature. This helps to warm up the catalytic converter.