Spark Control (Spk)

Fig. 35 Spark Control System:

Fig. 37 Spark Control System Operations Chart:

The Spark Control system delays the vacuum advance when the engine is hot. Combustion chamber temperature is lowered, thereby reducing NOx and HC. The system also improves cold engine performance by advancing ignition timing when coolant temperature is below 77°F. The system components consist of a bimetal vacuum switching valve, (two on M/T models), and a vacuum check valve.