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This page will cover the Start Sequence of the Alfa 75 TS fitted with Bosch Motronic ML4.1 EFI
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75 TS Start Sequence


The four relays on the firewall are, from left to right: (This may be different on your car)

S12a   Fuel Pump Relay
S12b   Motronic Relay
S12c   VVT Relay
S12d   Aux Motronic Relay

Turning on the ignition switch (to run or start):

1/ Provides power to the switched contacts of S12a (Fuel Pump Relay) (but does not turn S12a on)
      and turns on S12d (Aux Motronic Relay).

2/ S12d (Aux Motronic Relay):
          provides power to the ignition coils,
          power to S12c (VVT Relay) (but does not turn S12c on)
          and turns on S12b (Motronic Relay).

3/ S12b (Motronic Relay)
          provides power to S12a (Fuel Pump Relay) coil (but does not turn S12a on),
          provides power to pin 35 of the ECU,
          provides power to the Idle Actuator (but does not turn it on)
          and provides power to the injectors (but does not turn them on).

          NOTE! S12b should have a diode inside it or in the Green/Black wire going to it.

4/ When the ECU detects the engine is turning (via the Crank Angle Sensor) it turns on S12a (Fuel Pump Relay).

5/ The ECU now controls the Ignition Coils, the Fuel Pumps (both together), the VVT, the Idle Actuator and the Injectors.