Basic Fuel Pump Concepts

Answers questions such as:

How does an electric fuel pump work?

How electric fuel pump works?

How do automotive in-tank fuel pumps work?

How do fuel pumps work?

In the context of the users of this website, a fuel pump is a device used to transport gasoline from the gas tank of the vehicle to the engine. Several different "divisions of two" can be applied to fuel pumps. The first is their actuation: mechanical or electrical. Mechanical fuel pumps uses action driven by the rotation of the engine itself to pump the fuel. While they have been used for fuel injected engines, it is not as practical because these engines need a minimum amount of fuel pressure to start. While some fuel pressure can be generated by the starter turning the motor, it is much more practical to use an electrical fuel pump which can supply fully operating pressure the moment that the ignition is switched on (and even before the engine rotates.)

Automotive fuel pumps can be broken into two categories: Fuel pumps for carburetor-equipped engines and fuel pumps for fuel injected engines. These pumps are very different. Because a carburetor does not generally use pressure to inject fuel into the engine, only a very few pounds of pressure (typically less than 10 psi) are required to push fuel into a bowl. The vacuum created by the rush of air into the engine sucks the fuel out of the bowl and into the intake, requiring no additional pressure from a pump.

Fuel pumps for fuel injected engines have an entirely different purpose. Not only do they provide the fuel to the engine, they must provide it in sufficient force so that a strong spray of atomized fuel is pushed into the intake airstream before being carried into the engine. The pressure of the fuel at the fuel injector is typically required to be in the 35 to 45 psi range. Several sources use 43.5 psi as a "standard" although this is not always the case. Some of the Walbro electric fuel pump kits that we sell are designed for standard pressure levels as low as 12 psi or as high as 73 psi.

The automotive fuel injection fuel pumps from Walbro can be further divided into "in-tank" and "inline". This refers to the location of the fuel pump and is self explanatory. All of these fuel pumps are cooled and lubricated by the fuel that passes through them, so it is necessary that a continuous flow of fuel be realized. If you read the section of this FAQ on "Fuel Pressure Regulation" you will learn more about how the regulation of fuel-injection systems ensures that this happens.

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