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What is a Fuel Injection Pump?

Jason C. Chavis
Jason C. Chavis

A device that pumps fuel into gasoline or diesel engine cylinders is known as a fuel injection pump. The pump is usually driven by a chain or toothed timing belt that is motivated by the gears in a crankshaft. This system is also linked to the camshaft, causing them to be intertwined. In traditional four-stroke engines, it rotates at half the speed of the crankshaft in order to enable the correct timing of the injection process. This occurs as the cylinder's compression stroke is about to begin.

These devices are distinctly different from a fuel pump itself, which is primarily responsible for the flow of the fuel from its container or fuel tank. This is the part of the system in which fuel is brought out of the tank and pumped along a system of tubes to the engine block. The fuel injection pump then pushes the fuel inside the cylinders.

Fuel injection pumps in diesel engines operate under high pressure.
Fuel injection pumps in diesel engines operate under high pressure.

Fuel injection pumps need to operate in high-pressure environments in order to keep the system in full containment. In modern systems this is at the level of 15,000 psi or higher. For this reason, mechanics or engineers who work on these systems, especially diesel, take great care for personal safety. The fuel injection pump itself can possibly push fuel into the human body, causing serious harm to an individual.

In larger models, a concept known as in-line injection is the normal model. In this system, the pistons work with a throttle, which can produce varying power levels in the engine. All of the cylinders are rotated at once and the amount of fuel taken in is adjusted by a volume control method.

Smaller engines, such as those in cars and light trucks, use a distributor pump to control the fuel injection process. The injector pumps gas or diesel into fuel lines, which is how the volume of fuel is controlled. The timing of the injection process is controlled by the crankshaft. Essentially, the faster a vehicle moves, the more fuel is injected into the internal combustion engine. This can be accented with the addition of a turbocharger or supercharger, which gives the engine more power.

The fuel injection pump is ultimately controlled by a device known as a governor. The governor cuts the supply of fuel in event that the moving parts of the engine become too hot and endanger its life. This has the bonus of controlling the speeds a vehicle can reach in order to conform to local laws.

Discussion Comments


@Halfstack- You make a good point about the dangers of a fuel pump, but luckily most vehicles are moving away from mechanical fuel injector pumps, except in some big diesel engines (tractors and heavy machinery). Few people will be working on fuel injection pumps in a diesel, unless they are experienced and know what they are doing.

Gasoline automobiles are adopting electronic direct injection systems that pump the fuel into the intake valves through injectors instead of a rotary pump. Diesel vehicles are adopting common diesel rail injection systems to pump the fuel into their cylinders. These systems are much safer, and they allow for more precise injection of fuel into the cylinders; improving fuel efficiency.


That is a good and important point about the potential for getting hurt when working with a fuel injection pump. It is best to use a fuel injection service when cleaning or repairs are needed.

Not every system is the same, either, so even if someone had good luck working on one, it doesn't mean they will another. Of course, the point is, accidents happen, so even when you know what you are doing, you could get hurt. Leave it to the pros.

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    • Fuel injection pumps in diesel engines operate under high pressure.
      By: Voyagerix
      Fuel injection pumps in diesel engines operate under high pressure.