Moto fuel pump operation

For an internal combustion engine to work, we need 3 elements: air, fuel and spark. In a carburation engine, the fuel is sucked by the depression generated inside the engine. In modern EFI electronic injection engines, the fuel is injected under pressure in the right amount and at the precise moment in the combustion chamber.

Under pressure

The gasoline pump is used on motorcycles with electronic injection (also in some carburetor with remote gas tank) to feed the injectors with a constant supply and proper pressure.

The components of the pump are usually submerged in the gas tank (in this way they are cooled and the noise of its operation is cushioned). Gasoline passes through the pre-filtro and then, already pressurized, to the filter.

This filtering phase is essential to eliminate solid waste that could damage the injectors.

Once filtered, the fuel passes to the pump, where it is pressurized. Normally this component works electrical, with 12 volts that come from the injection system control relay. There are pumps of various types (rotor, turbine, lobes, rollers ...) But the function of all of them is to transfer gasoline from the deposit to the injectors.

They usually work continuously, providing a constant flow that raises fuel pressure.

The regulator

The pressure regulator is a mechanical system, composed of a spring and a valve, which eliminates the excess pressure generated by the pump, returning part of the gasoline back to the fuel tank.

In this way, a constant fuel supply is achieved, both in flow and pressure. This is very important, since in this way we will always obtain the same amount of gasoline every time the injectors are opened, regardless of the engine RPM (it will then be the injector that provides greater or lesser amount of fuel depending on the time of time than remains open).

Integrated in the pump system, a fuel level meter is usually installed, which usually works by a float with variable resistance or ultrasound.

The high pressure connector

Normally, pressurized gasoline is driven to injectors by a reinforced hose,

connected directly to the injectors at one end and at the exit of the regulator through a quick shot located outside the fuel tank.

Breakdowns and diagnosis

There are two main types of breakdowns in the fuel system: electric and mechanics.

The most common electrical breakdowns are the lack of voltage in the pump circuit or the overheating of the internal components, which can melt the pump. To avoid overheating, it is important to avoid rolling frequently with the very low fuel level (remember that cooling gasoline and lubricates the components of the pump).

At the mechanical level, the internal components of the pump usually fail. A rupture of the regulator that generates a pressure loss in the system is also very frequent. Similarly, internal sleeves can be drilled due to friction with the walls of the tank, creating pores and pressure loss.

The most used instrument to check the operation of the fuel system is the pressure meter, which connects interspersed at the pump output, before the injectors.

The pressure must be constant to any range of revolutions and must be found among the pressure specifications that the manufacturer marks in the specific workshop book and model.

 

Frank Burguera

#mecanicaharley