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EFI Electronics and Sensors Diagram
The electronics and Sensors diagram is typical wiring diagram for an EFI system. Some EFI systems may have more or fewer sensors than this drawing. This represents a typical fuel injection system. The engine and air temperature sensors are simple devices that change in resistance as the temperature changes. The MAP and TPS sensors provide a 0-5 volt signal back to the EFI system depending upon the amount of pressure in the intake or the position of the throttle. The Oxygen Sensor provides a 0-1 volt signal back to the EFI system depending upon the air/fuel ratio at the exhaust. The injectors have a 12 volt power supply to them at all times. The ECU activates the injectors by switching the voltage to ground. The idle solenoid is activated by a 12-volt signal and allows additional air into the intake manifold to increase the idle RPMs. The main relay is activated by the ignition switch and provides power to all components in the EFI system. The fuel pump relay is activated by the EFI ECU when the engine is running. If the engine stalls, the ECU will deactivate the relay and shut the fuel pump off as a safety feature.
In this drawing the coil or tachometer signal represents the EFI "trigger" signal. In the case of a sequential injection system like the Harley-Davidson EFI systems, this would be Crank Position Sensor.
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