Fuel Injection Systems

Fuel injection equipment before the 1920s was designed and manufactured by the engine manufactures. Bosch of Germany saw the need for precision mechanical fuel injection components and developed a “jerk” pump with “port and helix” metering. Using these principles and modern manufacturing methods, Bosch was able to produce reliable, positive displacement fuel injection equipment for engine manufacturers who did not produce their own.

The jerk pump Is a positive displacement pump with a close fitting  piston (plunger) in a cylinder ( barrel) that displaces whatever fuel is in the barrel when the plunger is forced into the barrel. The intermittent rapid movement of the plunger gives rise to the term jerk pump.

Today, the jerk pumping principle is used by the majority of fuel injection equipment manufacturers. Variations between different types and brands of fuel injection equipment are due mainly to differences in hardware and the fuel delivery requirements of specific engines.

Basic Plunger and Barrel

Let us consider what a plunger and barrel in a fuel pump must do. The plunger must be able to displace fuel at high pressure in varying quantities and throughout a wide range of engine speed. To accomplish this with precise control, a very close fit must be built into the plunger and barrel. The final step of the manufacturing process is the selective fitting of individual plunger to individual barrels. The technician should remember not to touch the finely lapped surfaces of these parts during service and to keep them as a matched set.

Basic Types of Fuel Injection Systems

The fuel injection system of any diesel engine  has six basic functions:

  1. To store, clean and transfer fuel
  2. To meter the quantity of fuel required at all loads and speeds and to equalize the fuel quantity delivered to each engine cylinders of multiple cylinder engines.
  3. To start injection at the right time within the cycle of the engine in relation to load and speed
  4. To ensure quick beginning and ending of injection so that the injected fuel is evenly atomized
  5. To inject the fuel at the rate necessary to control both combustion and pressure in the cylinder
  6. To direct, distribute and atomize the fuel uniformly, as required by the combustion chamber design

Two basic types of fuel injection systems are produced today, with many variations of each type. In later chapters we will go into each system in more detail. Listed below each group you will find some of the manufacturers of each type of system.


A gear or cam driven high pressure pump which supplies highly pressurized fuel by way of high pressure fuel lines to injector nozzles for atomization and injection (fig 28-1)

  1. American Bosch
  2. CAV
  3. Caterpillar
  4. Robert Bosch
  5. Stanadyne
  6. Diesel Kiki


A gear or cam driven low-pressure pump which supplies fuel to each cylinder’s unit injector. The unit injector  then highly pressurizes, atomizes and injects the fuel (Fig 28-2).

  1. Caterpillar
  2. Cummins
  3. Detroit Diesel


Recently, the control of fuel injection has begun to shift from mechanical control to computerized electronic control. In later chapter you will become more familiar with something new engine fuel control systems that have electrical linkage between the operator’s speed control and the engine! Some examples of these are:

  1. Programmable Electronic Engine Control (PEEC), which is produced by Caterpillar Inc. (Fig 28-3)
  2. Detroit Diesel Electronic Control (DDEC), which as the name implies is produced by Detroit Diesel Allison (Fig 28-4)

No matter what type of system you are concerned with, it is very important that each component be serviced properly in a clean, dust free environment. Shops whish specialize in fuel injection equipment service will often have a “clean room” as pictured in fig 28-5. Some go so far as to pressurize their clean room with filtered air to keep dust to a minimum. Any effort to keep fuel injection components clean will be rewarded by longer engine life.

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