Distributor Modulator System

The purpose of the distributor modulator system was to help reduce carbon monoxide and hydrocarbons.

Distributor modulator system was standard equipment on some 1970 Ford Mercury Lincoln vehicles. We see it only on the 1970 Mercury Cougar and Ford Mustangs with the M code 351-4V Cleveland engine and FMX automatic transmission.

The purpose of the distributor modulator system was to help reduce carbon monoxide and hydrocarbons. Sometimes it is referred to as the Dist-o-vac system. The basic premise of the system was to use carburetor venturi vacuum to reduce engine emissions. This was performed by controlling distributor spark advance. A retarded spark provides hotter combustion chamber and exhaust manifold temperatures that cause more complete burning of the fuel.

The three main components are the Electronic Control Module, Speed Sensor, and Thermal Switch.

• Electronic Control Module is the black box which houses the PC board and solenoid valve. Ford part D0AF-9E718-S, in the manual it is described as having a black box and a blue cover, we also see them with black covers on the black box.

  *Side note – There is also a white colored box along with black, blue, and white covers. This combination of boxes and lids make for 6 differently identified units for a range of other applications.

• Speed Sensor this actually is often confused with a cruise control part. It mounts inline on a two piece speedometer cable, it also has a two wire plug coming out of it. Ford part number D0AF-9E731-A.

• Thermal Switch this measures temperatures and only engages the modulator system on, at temperatures above 58°F. Ford part number D0AF—12A164-B.

For a 1970 Mercury Cougar or Ford Mustang the black module box will 'cut in' at speeds of approximately 23 mph and 'cut out' when speeds fall below 18 mph, provided that ambient temperatures are about 58°F.

There is other related wiring and vacuum lines involved that we will try and include. There were also two similar systems on the 1972 Mercury Cougars. TRS Transmission Regulated Spark and ESC Electronic Spark Control are the names of the two systems.  As time and information presents itself, we will include that system in the future.