In this chapter you have learned that the fuel delivery system pumps fuel from the tank to the engine where it is delivered by an electronically controlled fuel injector.

The fuel pump delivers fuel with enough pressure and volume so the fuel pressure regulator can hold a constant pressure differential between intake manifold and fuel rail. Fuel which is delivered to the fuel rail but not injected into the cylinders is returned to the tank through a return pipe.

The fuel pump is energized by the circuit opening relay electrical circuit whenever the ignition switch is on and the engine is running or cranking. Depending on fuel demand, some pumps are operated at two speeds by routing current flow through or around a special current limiting resistor. The fuel pump electrical circuit has a diagnostic monitor built into the underhood check connector for diagnosis and testing.

Fuel injectors are electrically controlled by the ECU and are driven individually, in groups, or simultaneously, depending on engine application. Current flow through the injector coil is controlled by using a high resistance coil or a separate injector solenoid resistor.

To improve cold starting, some engines are equipped with a cold start injector system which is controlled by a start time switch and/or the ECU.

Reprinted with permission from Toyota Motor Sale, U.S.A., Inc. from #850 EFI Course Book.

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