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What are the Symptoms of Bad Fuel Injectors?


Fuel injectors are an essential part of your car’s engine, delivering fuel at the right time to ensure clean and efficient combustion. However, without regular maintenance, fuel injectors can develop faults or become clogged, so you need to know how to spot the signs of a bad fuel injector how to fix it.

Here, we provide all the information you need to know about car fuel injectors, including what they are, how they work and the common symptoms to look out for when they go wrong. Use the links below to navigate the guide.

What Are Fuel Injectors?

Fuel injectors spray fuel into a car’s engine using electronic controlled valves, capable of opening and closing many times a second. They have an atomising nozzle that distributes the petrol or diesel evenly, for optimum combustion and efficiency. Injectors were introduced as a replacement for the old carburettor system, since they help engines run with greater fuel efficiency and also help to reduce emissions.

A car generally has one fuel injector per cylinder. So, if you drive a four-cylinder car, it will most likely have four fuel injectors.

How Do Fuel Injectors Work?

Fuel injectors control the volume of fuel delivered to the combustion chamber, ensuring the right amount is injected at the right time. The process is:

  • The fuel pump pushes petrol or diesel through the fuel lines to the injectors.
  • The ECU (engine control unit) uses sensors to work out the right time to fire the injectors and spray fuel into the combustion chamber.
  • When the ECU activates the injector, pressurised fuel is sprayed into the combustion chamber through the nozzles. Because the nozzles are so small, the fuel is atomised, which makes it burn more efficiently.

Signs and Symptoms of a Faulty Fuel Injector

Sometimes fuel injectors can develop faults which impact on their performance or cause breakdowns. This is often due to them becoming clogged with debris, although some mechanical and electrical issues can also affect fuel injectors.

Here, we take a look at some of the common signs and symptoms associated with a faulty fuel injector.

Check Engine Warning Light

The most common sign of a bad fuel injector is the check engine warning light, which appears on the dashboard. As soon as an injector isn’t doing what it should, this light will come on. (In other words, if it’s adding too much or too little.)

Although there are a few different reasons why a check engine light can switch on, it could be down to a fuel injector. The ECU triggers the warning light when the injector is delivering too much or too little fuel.

Misfiring or Vibrating Engine

Does your car often misfire? Or, maybe there’s a delay after you press the accelerator pedal? Both of these symptoms can be caused by a faulty fuel injector, most likely a clog or blockage in the nozzle.

If the injector can’t deliver the dose of fuel called for by the ECU, the fuel-air mix in the combustion chamber will be off, which can lead to misfiring or a sudden drop in acceleration. That’s why it’s so important to keep your car’s fuel injectors clean and free from blockages.

Rough Idle

If your car’s idle noise has changed and feels rougher, the fuel injectors may not be delivering fuel as they should. As with misfiring, this is normally down to the injector nozzles being clogged with particles, which interfere with the atomisation and spray of the fuel.

Several faults can cause a rough idle noise, including a bad spark plug or a dirty air filter, but clogged injectors are one of the most common reasons for this.