Fuel Injection

The diesel fuel injection system pressurizes the fuel and then injects it into the compressed air in the combustion chamber. If one or more of the fuel injectors fail, the engine won’t run – or if it does, it’ll run very poorly. Because diesel isn’t as clean as gas, the injectors get dirty faster and should be cleaned more often. A diesel mechanic at RDI Power (RedLine Diesel, Inc.) can repair your diesel engine’s fuel injection system if it fails.

RDI Power mechanic performing a fuel injection

The Fuel Injection System

The diesel fuel injection system is not a complicated system, but it does take more maintenance than a regular gas fuel injection system. The diesel version consists of:

  • A fuel injection pump that pressurizes the fuel.
  • A high-pressure pipe that sends the fuel to the injection nozzle.
  • A feed pump that sucks the fuel from the fuel tank.
  • Fuel filters that filter the fuel.
  • A water separator or fuel sedimenter in the fuel filter that separates the condensation from the fuel.


When the cam in the fuel injection pump lifts the plunger, it compresses the fuel, then pumps it to the injector. Injection timing makes sure the fuel is delivered into the combustion chamber at the proper time. When the fuel goes through the injector, it is atomized and mixed with air, then it combusts, giving the engine its power.

Unlike a gas vehicle where the air and fuel need a spark for combustion, a diesel compresses air, which makes it hot. When the atomized fuel hits it, it causes an explosion – combustion.

Diesel Fuel Filters

Most diesel systems have more than one fuel filter. Most have a screen at the tank, the primary fuel filter, and a secondary fuel filter. If the filters are in a series, all of the fuel goes through each of the three filters in a row. If the filters are parallel, some fuel goes through each one of the filters. All of the filters must be changed during maintenance.

Mechanical and HEUI Fuel Systems

A diesel engine could have one of four different types of fuel injection:

  • One pump and injector for each cylinder.
  • A unit injector type – a combined pump and injector for each cylinder.
  • A distributor type – one pump for more than one injector – four on a four-cylinder, six on a six-cylinder, and eight on a V8.
  • The common rail system where the pumps are in a common housing with injectors for each cylinder.
An RDI Power technician cleans out part of the fuel injection system

Fuel Injection's Main Enemy

The diesel fuel injection system’s main enemy is water, and diesel has more water in it than you would think. If the water makes it through the filters and into the injection system, it will rust the steel components. This could cause the injectors to seize, the metering components in the injectors and pump to stick or cause a governor or metering component to fail. Thus, it is imperative that you make sure you change the fuel filters as recommended by the manufacturer.

Contact RDI Power

When it’s time to service your diesel, including servicing the fuel injection system or make repairs to fuel injection systems, contact our auto repair shop in Spring Hill Fl. at RDI Power to schedule a maintenance or repair appointment.