Electronic Spark Control System - CAPRI: Operation

Vacuum is retarded by distributor modulator valve inserted in vacuum line between distributor and carburetor vacuum advance port. Valve is normally open, when electrically energized it closes, cutting off vacuum to distributor, thereby preventing vacuum advance. The ambient air temperature switch, located in right door pillar post, senses outside air temperature. A temperature of 49°F will cause the switch contacts to open breaking the electrical circuit, allowing normal advance at all speeds. A temperature of 65°F will close switch contacts. This will cut off vacuum to distributor and retard ignition timing. The speed sensor located in the speedometer cable will generate a voltage frequency proportional to vehicle speed. This voltage is transmitted to the electronic amplifier, which opens or closes distributor modulator valve. When vehicle speed reaches 37 or 40 MPH, depending on engine application, a signal from the speed sensor triggers the electronic amplifier and the distributor modulator valve opens permitting normal vacuum advance. When speed is decreased to 18 MPH, electronic amplifier energizes distributor modulator valve, which retards ignition timing. The electronic amplifier is mounted on a printed circuit board located in control module.