310 Auto Engine Repair Copyright by Goodheart-Willcox Co., Inc. Figure 15-6. Many new engine designs use direct gasoline injection. Because fuel is sprayed into the combustion cham- ber at very high pressure, the liquid gasoline atomizes into a fine mist for more complete combustion of hydrocarbons. (Ford) Fuel tank In-tank filter In-tank fuel pump Power source ECM Wiring harness Engine sensors Fuel injectors Vacuum hose Fuel pressure regulator Fuel return line Fuel rail Fuel feed line Inline fuel pump Inline fuel filter Figure 15-7. Study the basic operation of a fuel injection system. A fuel pump forces fuel to the fuel rail, which supplies the fuel injectors. A pressure regulator limits fuel pressure and bleeds excess fuel into the return line. Fuel constantly circulates through the system. Engine sensors report engine conditions to the computer. The computer can then open injectors as needed. Fuel return line Fuel pressure regulator Cold start valve Fuel supply line Fuel manifold or rail Fuel injectors Intake manifold Fuel tank Electric fuel pump Fuel filter Figure 15-8. A fuel pressure regulator is mounted on or next to the fuel rail in multiport fuel injection systems. It is mounted inside the throttle body in throttle body fuel injection systems. • Fuel return line. A line and hose assembly that carries excess fuel back to the tank from the pressure regulator. • Injectors. Solenoid-operated fuel valves that open when energized by the ECM. • Electronic control module (ECM). A computer that processes sensor data to determine when and for how long injectors should be opened based on operating conditions. • Sensors. Electronic devices capable of changing internal resistance or voltage output with a change in a condition, such as a change in temperature, pressure, or position.