Fuel Pump Information

There are two main types of fuel pumps: electric and mechanical and each can be rated by pressure and by volume. This page will discuss the differences and selection criteria needed to select the proper fuel pump for your application.

Mechanical Fuel Pumps - The mechanical fuel pumps are driven typically by a lobe on the camshaft. They are mounted on the side of the engine and have a lever that mates with a rod that connects to a lobe on the camshaft.

They are pull type pumps where they pull the fuel from the tank. That's why they are mounted at the front of the vehicle next to the engine. Typically, they are used with carburators and maybe some throttle body injection. Most modern vehicles do not use mechanical fuel pumps.

Electric Fuel Pumps - Electric fuel pumps are powered by the 12 volts of the electrical system. They are considered to be more efficient than a mechanical pump - they use less energy than a mechanical pump.

They are push type pumps and work best when they are pushing fuel. They are typically located at the fuel tank end of the vehicle or in the fuel tank. They are typically used with fuel injection and can be used with carburators. If you have an older mechanical type fuel pump, you can add an electric fuel pump at the gas tank to help deliver the fuel.

Low Pressure Fuel Pumps - Low pressure fuel pumps provide fuel pressure in the range of 5-12 psi of fuel pressure. They are used with carburators (5-7 psi) and throttle body fuel injection (10-12 psi). Carburators have a fuel bowl that holds a small amount of fuel that is regulated by the carburator while driving. The fuel level and pressure is critical for proper operation.

The fuel level in the fuel bowl is controlled by the float mechanism. If you use a high pressure fuel pump with a carburator, the float will not be able to regulate the level and the carburator will be flooded with fuel - not a good thing! Typically, mechanical fuel pumps are low pressure pumps - but that is not always the case.

High Pressure Fuel Pumps - High pressure fuel pumps provide fuel pressure in the range of 40 - 60 psi. They are used with sequential electronic fuel injection. The fuel injectors require high pressure to work properly.

Most often they are electric fuel pumps and are located in the gas tank. There are some mechanical high pressure pumps that are located at the engine but they are not common.

A fuel injector is rated in lb/hr of fuel at a specific pressure. If you increase the fuel pressure, the fuel injector will appear to be a slightly larger injector and flow more fuel. Here's some details on fuel pressure vs. injector size. You can control the fuel pressure by using an adjustable fuel regulator.

Volume - Volume is fuel pump rating that spec's the amount of fuel flowing at a given psi. This is an important rating that is determined by your engine requirements. It is typically rated in litres/hour (even though pressure is in psi -Imperial!).

A monster engine like a 440 cid (7.2L) Mopar will need lots of volume of fuel flowing at the same psi compared to a 1.5L Honda engine.

The fuel pump must be spec'd to provide the needed fuel volume or else the engine will have fuel starvation at the higher rpm when the fuel is needed. Fuel starvation creates a lean mixture which can raise combustion temperatures and burn valves and pistons.

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Copyright April 2011 Eugene Blanchard