Vacuum Retard System

The 1974 2002 tii, is equipped with a vacuum retard unit only. The retard unit receives its vacuum from intake manifold during deceleration and idle to help reduce exhaust emissions.

The distributor on all 1975-77 models is equipped with a vacuum retard unit. No vacuum advance unit is used. By retarding ignition timing, a larger throttle opening can be obtained, thus improving combustion.

On 1975-76 530i and 3.0Si California models, a vacuum solenoid valve is installed in the line to the retard unit. The vacuum solenoid valve is controlled by an engine speed sensor, which shuts off vacuum retard at engine speeds over 3000 RPM.

On all 1977 4-cylinder engines, the vacuum supply to the retard unit is controlled by a timing valve, which eliminates ignition retard until engine warms up.