Description & Operation: Notes

The Electronic Distributor Modulator reduces engine emissions through close control of distributor spark advance during specified conditions of acceleration and deceleration. System consists of four major components: a speed sensor, a thermal switch, an electronic control amplifier and a three-way solenoid valve controlling vacuum applied to the distributor. Control amplifier and solenoid valve are combined as a single unit and mounted inside passenger compartment on dash panel. Speed sensor is connected to speedometer cable. Thermal switch is mounted near front door hinge pillar on outside of cowl panel. It may be mounted on either right or left side. The modulator operates to prevent spark advance below a specified speed when accelerating and also prevents advance below a specified value on deceleration. Operating speeds vary according to engine, (see specifications  below).