Fuel Supply

Introduction:

The fuel supply, from the fuel tank to the injector valves, for most systems except GDi, follows the same basic layout. A fuel pump is fitted either in or close to the fuel tank. A fuel filter is fitted in the delivery fuel lines from the tank to a fuel rail.

 

Layout of fuel supply components:  
 

 

• A fuel pump is fitted either in or close to the fuel tank.
• A fuel filter is fitted in the delivery fuel lines from the tank to a fuel rail.
• A fuel pressure regulator is located on either the housing for throttle body injector systems or the fuel rail for port fuel injection systems.
• Return fuel lines run from the pressure regulator to the fuel tank.

 

Roller cell pump

• The fuel pumps on injection systems are usually roller cell types, driven by a permanent magnet electric motor.
• Fuel flows through the pump and motor, but there is no risk of fire as there is never an ignitable mixture in the motor.
• The pump delivery pressure is set by a pressure relief valve, which allows fuel to return to the inlet side of the pump when the operating pressure is reached.
• There is also a non-return valve in the pump outlet. Typical delivery pressures are between 300 and 400 kPa (3–4 bar).
• The rollers in the roller cell pump are thrown out by centrifugal force when the motor armature and pump rotor spindle rotate.
• The rotor is fitted eccentrically to the pump body and as the rollers seal against the outer circumference, they create chambers that increase in volume to draw fuel in.
• They then carry the fuel around and finally discharge it as the chamber volume decreases

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The fuel pump electrical supply is live only when the engine is being cranked for starting or is running. The fuel pump electric feed is from a relay that is switched on with the ignition. Safety features are built into the electric control feed to the relay so that it operates only to initially prime the system or when the engine is running.