### Spark Timing Control System

The spark timing control system has been used in different forms on Nissan/ Datsuns since 1972. The first system, Transmission Controlled Spark System (TCS) was used on most Nissan/Datsuns through 1979. This system consists of a thermal vacuum valve, a vacuum switching valve, a high gear detecting switch, and a number of vacuum hoses. Basically, the system is designed to retard full spark advance except when the car is in high gear and the engine is at normal operating temperature. At all other times, the spark advance is retarded to one degree or another.

The 1980 and later Spark Timing Control System replaces the TCS system. The major difference is that it works solely from engine water temperature changes rather than a transmission mounted switch. The system includes a thermal vacuum valve, a vacuum delay valve, and attendant hoses. It performs the same function as the earlier TCS system. To retard full spark advance at times when high levels of pollutants would otherwise be given off.