Ignition Timing Control System

Fig. 131 Ignition System Advance Vacuum And Wiring Diagram (PGM-FI Engine):

Ignition timing control, combined with the internal distributor control (centrifugal advance), affects the time which each spark plug ignites the air-fuel mixture, in accordance with engine speed, load, and coolant temperature. This optimizes ignition timing during and after engine war-up to maximize fuel economy and performance.
The distributor has two separate vacuum advance diaphragms which operate on manifold vacuum. Diaphragm A is connected directly to the intake manifold, and diaphragm B is also controlled by the ignition control solenoid valve. It is operated by the ECU which receives signals from the engine coolant temperature, engine speed, and manifold vacuum sensors. When the ignition control solenoid valve is open, it sends vacuum to diaphragm B to improve cold engine performance by advancing the timing until the engine warms up.