Fuel Delivery Systems

Fuel Pump Relays

Producing adequate fuel pressure and volume is the “bottom line” for fuel pump performance. The fuel pump relay is an electric switch that’s commanded on or off by the Powertrain Control Module or PCM when the ignition key is initially turned on for approximately three seconds to pressurize the system, then again once the key goes to start, the PCM activates the fuel pump relay again. Once the engine starts, the PCM get input from the crankshaft sensors it either turns the pump off or keeps it running. Many modern vehicles have an inertia switch to turn off the fuel pump in the event of an accident. Anti-theft devices can deactivate the fuel pump if it detects tampering.

Modern Fuel Pumps, Filters, and Regulators

The pressure required to vaporize the fuel in modern engines is generated by a high-pressure electric fuel pump in the fuel tank. Depending upon the type of fuel injection system, most fuel pumps generate between 15 to 90 psi of fuel pressure. Many fuel pumps are protected from dirt by a fuel strainer attached to the fuel inlet. The fuel injectors are protected by a fuel filter downstream of the fuel pump. It’s important to remember that in-line fuel filters are frequently neglected and should be changed at the first sign of fuel delivery system trouble.

In contrast, many modern fuel filters are located inside the fuel tank on the inlet side of the fuel pump and last the life of the pump. The fuel pressure regulator ensures accurate fuel delivery by precisely controlling fuel pump pressure. There are two types of pressure regulators: dual-line, and single-line. Dual-line systems return the excess fuel using a second line. Single-line fuel injection systems contain the fuel pressure regulator into the fuel pump assembly and rely on the ability of the Powertrain Control Module (PCM) to maintain fuel control by changing the amount of time the fuel injector remains open.

Regular maintenance to your fuel system includes;

  • Using a fuel system additive to clean the system
  • Replacing the fuel filter when it is due
  • Replacing your air filter when it is required
  • Servicing and cleaning the fuel injectors as required.
  • Common fuel system faults include:
  • Poor fuel economy
  • Poor throttle response and lack of power
  • Stalling problems
  • Unable to start the car

Fuel is delivered to the fuel injector under pressure and fuel is released from the injector into the inlet manifold when it receives a pulse signal from the ECU. The amount of fuel delivered is determined by the length of time of the pulse signal from the ECU. The fuel filter can be mounted in the fuel line between the fuel pump and the injectors or can be part of the fuel sender unit in the fuel tank which often also houses the fuel pump.