Spark Timing Control System: Description

NOTE: California automatic transmission equipped pickups (except heavy duty models) are equipped with a vacuum delay valve only.

The Spark Timing Control system is designed to control distributor vacuum advance under varying driving conditions to reduce HC and NOx emissions. This is accomplished through the use of thermal vacuum valves (TVV) on all models (except pickups). Thermal valves are major components of the EGR system. In addition to thermal vacuum valves, a vacuum delay valve (one-way valve) is installed on all models (except all 200SX and 510 models, Federal 210 models with Auto. Trans. and California 280ZX and 810 models.

NOTE: Federal 280ZX and 810 vacuum advance line is actuated at normal operating temperature. At idle, manifold vacuum is regulated by orifices and spark timing is advanced half-way.