Maximum Engine Speed Limiter
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 1987 Volkswagen Scirocco, 1987 Volkswagen Quantum, 1987 Volkswagen Jetta, 1987 Volkswagen Golf, and 1987 Volkswagen GTI. However, it is still accessible from the selected car via links, so may be relevant.
ECU senses engine speed based on impulses from terminal "TD" of ignition switching unit. Maximum engine speed is controlled by adjusting current supply to the differential pressure regulator from ECU. Lower chamber pressure in the fuel distributor is increased to limit fuel flow to the injectors. When maximum engine speed is reached a signal from the ECU will interrupt the fuel pump relay signal and shut off the fuel pump.