To have an efficient-running engine there must be the correct amount of fuel. To provide this fuel must be stored, pumped out of storage, piped to the engine, filtered and delivered to the fuel injectors. Fuel delivery is an important system in automobiles. Modern fuel delivery systems are designed depending on the type of fuel used and the performance required by the automobile. The fuel delivery system also ensures the cleanliness of the fuel as it passes through the fuel filter. All engines require a method to store and deliver fuel to the engine, the fuel delivery system does this in a vehicle and the main purpose of the fuel delivery system is to supply the fuel and run the engine.

The fuel systems in today’s vehicles is designed to prevent fuel vapours from entering the atmosphere. They are normally called a return-less on demand system. In older systems, a fuel pump delivered fuel under pressure to the injectors. A pressure regulator at the injectors controlled the fuel pressure by sending excess fuel back to the fuel tank. This is a return fuel system. In a return-less system, the pressure regulator is within the fuel tank and excess fuel is released to the tank. There is no need for a return line. In a return system, the fuel sent back to the tank has been heated by under hood temperatures. The introduction of the warm fuel to the tank causes the fuel to evaporate. Fuel pressure and volume are controlled by the PCM according to the existing operating conditions.

Fuel pump relays:

Producing adequate volume and pressure is the bottom line for fuel pump performance. A fuel pump relay is an electric switch that is directed on or off by the powertrain control module (PCM). The ignition key is turned on initially for a period of 3 seconds in order to pressurize the system, when you go to start the vehicle, the PCM helps to activate the fuel pump relay again. Once the engine starts, the PCM gets signals from the crankshaft sensors to either turn off the pump or keep it running. Modern vehicles have an inertia switch to turn off the pump in the event of any accident so that no fuel from the tank is spilled all over the wreckage which could cause a fire and worst case an explosion.

Pulse modulated fuel pumps:

These systems help to eliminate the need of a fuel pressure regulator by controlling the pump speed to change the fuel pressure. In pulse modulated systems, the PCM uses a pressure sensor that is mounted on the fuel line to monitor the fuel pressure. These systems also require scan tools to monitor the diagnostic trouble codes and to test the system by directing the fuel pump to produce different pulse rates.


  • Fuel pumps are protected by a fuel strainer which is attached at the fuel inlet. Similarly the fuel injectors are safe guarded by the fuel filters attached to the inlet of fuel and downstream at the fuel pump.
  • In case if the fuel delivery system malfunctions, the first sign may be traced out at the fuel filters.
  • In modern vehicles the fuel filters are placed inside the fuel tank at the inlet side of the fuel pump.


  • The pressure regulators ensure optimum fuel delivery by controlling pressure of the fuel pump.
  • The pressure regulators are of two types.
  • The dual-line system returns excess amount of fuel using a second line.
  • Single-line fuel injection systems have a fuel pressure regulator and it depends on the PCM to maintain fuel levels.

Auto manufacturers are installing a sophisticated diagnostic system in to their PCM’s in order to help the mechanics to quickly diagnose the fuel systems. The PCM monitors the fuel delivery system performance by monitoring the oxygen sensor voltage. The PCM holds the fuel injectors open for a longer time to maintain correct oxygen sensor voltage, when the fuel pressure is low or if a vacuum leak develops. Modern vehicles are more about on board electronics. The diagnostic system contains rich and lean commands when the ratio of air fuel mixture is not appropriate.

All info was extracted from google search and from “Automotive technology: A systems approach; 5th addition – Jack Erjavec”.

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