Description & Operation
The transmission Regulated Spark Control System (TRS) reduces engine emissions by retarding distributor vacuum advance while vehicle is in first and second gear. System consists of a distributor modulator valve, ambient temperature switch and transmission switch. In some applications a spark delay valve is also used. Vacuum is controlled by distributor modulator valve located in vacuum line between carburetor and distributor. This valve is normally open and closes off vacuum supply to distributor when energized. An ambient temperature switch in either right or left front door post senses outside air temperature. A temperature below 49°F will cause switch to open and allow normal vacuum advance in all gears. A temperature of 65°F will close switch and allow normal operation of TRS system. On manual transmissions a switch is mounted on left side of the case. When gear lever is moved to high gear position, switch plunger enters a detent on shift rail to open switch. On automatic transmissions, switch is operated by transmission fluid pressure in high range or reverse gear circuits. When transmission switch contacts are opened (manual or automatic), the modulator valve is de-energized, restoring normal vacuum advance.