Power supply system (Mazda Capella GD)

This system supplies the injectors with the gasoline required for combustion at a constant pressure. Fuel is metered in the intake manifold and injected in accordance with injection control signals. Fuel pump, fuel filter, supply line, pulsating damper, injector pressure regulator, fuel pump switch (built into the air flow meter) and the system relays are other parts of this section of the installation. The fuel pump is located in the tank. The injectors are supplied with current directly through the main relay. The following description serves to better understand the workflow (see figure 139).

• The air flow meter (13) determines the amount of incoming air and sends a corresponding signal to the engine control unit. The intake air temperature sensor and fuel pump switch are built into the flow meter.
• The atmospheric pressure switch (7) detects the atmospheric pressure and transmits the corresponding signals to the engine control unit.
• The system relay (11) supplies voltage to the fuel pump while the engine is running.
• The clutch pedal switch (10) signals the engine control unit when a gear is engaged.
• The engine control unit (8) regulates the operation of the fuel injection system.
• The fuel pump only operates when the engine is running.
• The idle speed switch, mounted on the throttle body, indicates when the throttle valve is fully closed and sends appropriate signals to the engine control unit.
• The valve injectors (1) are controlled to inject fuel using signals from the engine control unit.
• The intake air temperature switch installed in the air flow meter transmits the corresponding temperature signals to the engine control unit.
• The main relay supplies current to the injectors and the engine control unit.
• The neutral switch (14) is switched on when one gear is engaged in the gearbox.
• The oxygen sensor transmits oxygen concentration data to the engine control unit.
• The pressure regulator regulates the pressure of the fuel supplied to the injectors.
• The throttle position sensor transmits information about the throttle valve opening angle to the engine control unit.
• The water temperature sensor (19) provides information on the temperature of the coolant for the engine, while the temperature switch (18) in the radiator is switched on at a temperature above 17°C and transmits a corresponding signal to the engine control unit.

6.3.1. Safety precautions when working with the power supply system

The fuel in the system is under very high pressure when the engine is not running. On this basis, the following instructions must be observed if work is planned for the installation:

• Start the engine and disconnect the relay terminals (11) in figure 139 (remove the plug).
• After the engine is turned off, also turn off the ignition.
• Insert the plug back into the relay.
• After loosening the connections, wrap a thick cloth around the connection areas to prevent fuel from splashing.
• All system checks must be performed using a special device, i.e. they must be left to the Mazda dealership.