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Common Symptoms Of A Bad Fuel Injector

By R&D
Published on December 22nd, 2023

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To discuss the five common symptoms of a bad fuel injector.


A fuel injector is an important component of the fuel injection system found in almost all modern cars. An injector is an electronically controlled mechanical device that is used to spray fuel into the engine to create the right mixture of air and fuel, which in turn allows the engine fuel to burn efficiently.

Without proper maintenance or faulty, a bad fuel injector can have problems, such as: 

  • Electrical Issues (malfunctions when receiving commands from ECU - Electronic Control Unit or Computer). 
  • Clogging or Blockage Issues — due to accumulation of dirt and/or debris (usually the most common injector problem).

It's essential to be alert for the signs of bad injectors so that you can act to resolve them quickly. The most common symptoms of bad fuel injectors are listed below.

Check Engine Light Illuminates

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One of the most obvious symptoms is the Check Engine light flashing on your dashboard. This light may indicate a problem with the fuel injection system. Once the injectors become clogged or dirty and are not fueling the engine efficiently, or when an injector fails, this typically leads to excessive or insufficient fuel getting to the engine (sometimes there's no fuel).

The Engine Control Unit (ECU) will detect fluctuations in the amount of fuel being injected into the engine, and consequently trigger the Check Engine light to illuminate. If the Check Engine light is flashing, determine the trouble code with an OBD2 code reader.

Rough Engine Idling / Stalling 

If you experience rough idle, or the engine stalls on low RPM, it could be a signal of bad fuel injectors. That happens when debris builds up at the injector nozzles, and affects the quantity of spray and atomization of gasoline. Although the rough condition may be attributed to grimy air filters, spark plugs or others components, it could suggest trouble from bad fuel injectors.

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Engine Misfiring

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The ECU monitors and controls the fuel injected into the engine, and if the injector fails to deliver the correct amount of fuel at the correct time, there will be issues with the fuel-air mix within the engine's combustion chamber. As a result, the engine misfires or the acceleration response is delayed. P0300 (Random Cylinder Misfire), P0301 (Cylinder number 1 Misfire), P0302, P0303, P0304, P0305, P0306, P0307, P0308 are examples of misfire codes.

Slower acceleration or shaking during acceleration suggest that an engine is misfiring. The engine may also hesitate or briefly lose power. The engine may run unevenly and vibrate more than usual at idle. Misfires can happen when an engine is cold or warm, and they can happen infrequently. The engine misfire is a serious problem and sometimes difficult to diagnose. 

Failed Emissions Test

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If your car has a bad fuel injector or is otherwise not operating as designed, you may have a faulty air/fuel mixture. If there is excess fuel that does not burn up during a normal combustion cycle, your car will produce more carbon dioxide than usual, which will be emitted out your tailpipe. Too many emissions at the tailpipe make the catalytic converter unable to do its job properly, as a result your car will fail an emission test. Emissions tests are performed using an OBD2 code reader.

Bad Fuel Odors 

If you notice a strong fuel smell in your cab while driving, you may have a fuel leak. In most cases, leaks are caused by an O-ring failure between the injectors and the fuel rails. Engine heat can make the O-rings brittle and cracked. When fuel injector O-rings are worn out or improperly maintained, they can develop a leak.


Fuel injectors are extremely important to the overall functionality and performance of your vehicle because they are  some of the main components that allow an engine to run. If you notice any of the previously mentioned symptoms, or suspect that there may be a problem with your fuel injectors or any other part of the fuel system, use a scanner tool to diagnose the problem and follow the steps in the relevant repair manual to fix it.

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