Fuel Injectors: functions, problems and symptoms

Fuel Injectors: functions, problems and symptoms

You don’t have to be an expert on internal-combustion engines to understand the importance of supplying the right amount of fuel and air to the engine cylinders for combustion. If the cylinders don’t receive enough fuel, the engine will run lean and it could lead to serious engine damage. For over a century, the carburetor was the most commonly used device for fuel delivery. However, by the 1990’s, these simplistic mechanisms were made almost completely obsolete by the more fuel efficient, powerful fuel injectors.

Are you having problems with your engine? It could be due to a faulty fuel injector. This article provides a maintenance guide for diagnosing injection problems to help you determine whether the components need to be replaced or repaired, and whether it is necessary to use fuel additives or fuel injector cleaners.

What is a fuel injector? How does it work?

How do fuel injection systems work

Modern fuel injectors are electronic valve mechanisms which spray pressurised liquid fuel into an internal-combustion engine. The atomised nozzle ensures that the fuel is evenly distributed and the valves are timed to achieve the optimal air-fuel mixture and engine consistency. The precision of this process is a key factor for engine performance. The ideal air-fuel ratio is 14.7:1, known as the stoichiometric mixture.

Fuel injectors are supplied by the fuel rail as the fuel is pumped through the rail and into the injector. The fuel passes through a tiny filter and is held in the component’s reserve. The electromagnetic coil then moves the plunger which opens up the pintle injector and triggers the spray nozzle. The timing of this is controlled by the car’s computer system.

Types of fuel injector systems

Different types of engines require different types of injectors depending on the needs of the car and fuel type. For example, they vary in terms of location, injection sequence, and operation.

 Most modern cars use one of the following electronic injection systems: 
  • Throttle body injection (TBI): One of the earliest fuel injection systems. It was designed as a cheap alternative to the carburetor. Similarly to the carburetor, Throttle body injectors inject fuel into the intake manifold, which then mixes with the air and is sucked into the engine cylinders. Although these systems have been developed over the years, they are still quite inaccurate.
  • Multi-port injection: These systems include a separate injector nozzle for each engine cylinder, installed on each intake port (multiple ports). Multi-port fuel injectors (MPFI) distribute the fuel more precisely to get the right air-fuel ratio and are therefore more efficient than TBFIs. However, all the injectors spray at the same time which can leave some fuel behind in the cylinders until the next intake cycle. The fuel can condense and become unusable.
  • Sequential injection: A sequential injection is the upgraded version of the MPFI system, as it addresses the issue of potential fuel waste. Instead of spraying the fuel at the same time, each nozzle is timed to spray fuel separately. The injectors spray the fuel just before or as the intake valve opens up.
  • Direct fuel injection: For this system, the fuel injectors spray the fuel directly into the combustion chambers, bypassing the intake valves. Direct injection is commonly used for diesel engines and has been developed since the 1920s. It is more accurate than other systems and can produce a high power output at low fuel consumption levels.
    Types of fuel injector systems: Direct Injection

Common problems

If these components stop functioning properly, it could lead to irreversible engine damage and the engine could eventually stop working altogether. Diagnosing and responding to fuel injector problems quickly can help you to extend the service life of your engine.

 Here are 5 common problems that drivers encounter: 
  • ! Clogging. There are several reasons why the fuel injector nozzle can become clogged, such as contaminated fuel, internal deposits and heat soak. Heat soak can occur after the engine has been switched off. Under hot conditions, the fuel residues can evaporate and leave behind a waxy residue which can clog up and block the air intake and injectors. Keeping the fuel and nozzle clean, changing the fuel filter and using special additives will help to prevent this.
  • ! Internal or external leaks. Leaks can occur due to issues such as overheating and seal or nozzle damage. If the injector is leaking, it will not be able to achieve the correct air-fuel mixture.
  • ! Solenoid failure. Most injectors include solenoid valves which work by creating an electromagnetic field to let out the fuel.
  • ! Installation errors. E.g. incorrect torque, missing parts or using the wrong cleaning technique.
  • ! A faulty engine control unit (ECU). The ECU monitors engine performance and controls the injection, ignition, exhaust and compression processes. If there is a fault, the ECU may not be able to ensure that the injectors mix and distribute the fuel properly.

Symptoms of a faulty fuel injector

  • ! Rough idling & stalling. The vehicle might shake and stall when idling if it is not getting enough fuel in the combustion chambers.
  • ! The engine misfires. Often caused by dirty or clogged fuel injectors.
  • ! A fuel smell. You might smell a strong fuel odour in and around your car if there is a leak or the injectors are releasing too much fuel.
  • ! Starting difficulties. When too much or too little fuel is being supplied this can prevent the engine from starting and lead to engine failure.
  • ! Increased fuel consumption.
  • ! The check engine light is on.
    Symptoms of a faulty fuel injector
  • ! Black or grey smoke. Black smoke is an indication that the air-fuel mixture is too rich. You can diagnose many different car problems by the colour of the exhaust gases. Read more about it here.


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