How To Test Fuel Injectors – All You Need To Know

Fuel injectors are an extremely important component of your vehicle. They spray gas into the engine’s cylinders.

The gas combines with air and is compressed prior to the combustion process, which involves igniting the spark plugs in order to create the power that is needed to move a vehicle.

How to Test Fuel Injectors

how to test fuel injectorsGiven the important role of fuel injectors, should a problem arise with one of these components, your engine – and your entire vehicle – can suffer greatly. For example, your engine will likely start lagging, and in the worst case scenario, it might not even work at all.

There are several reasons that could lead to failed fuel injectors. While some of the reasons may be outside the realm of expertise that a DIY mechanic possesses, often, failed fuel injectors can be diagnosed on your own using the following methods.


Listen to Your Fuel Injectors

Pop open the hood on your vehicle and find the fuel injectors.

  • If you aren’t sure where they are located, refer to your vehicle owner’s manual.
  • Most makes are outfitted with a single fuel injector for each cylinder.
  • Typically, they are situated on the intake manifold and a fuel rail connects them. The fuel rail is the cylinder running across the top part of the intake manifold.
  • Each fuel injector will be located between the fuel rail and the intake manifold.
  • If you have a V6, V8 or V19 engine, there will be two fuel rails, and half of the fuel injectors will be located on each side of the engine.
  • Next, grab a long screwdriver or a long, thin piece of metal that’s about a foot in length.
  • Touch the tip of the screwdriver on top of one of your fuel injectors and hold the other end upwards at an angle.
  • Let the engine run and bring your ear close to the end of the metal that isn’t touching the fuel injector.
  • The metal will transmit sound from the fuel injector, allowing you to determine if there is an issue.
  • If you aren’t able to hear a clicking sound, that is an indication that there is a problem with either the injector or the electronic control that connected to the injector.

Follow the same process as mentioned above with each fuel injector.  If you hear a clicking sound for each one, which is the sound of activation, all is fine.

Check out this handy vid from ChrisFix for more help with this method:


Make Sure the Fuel Injectors are Getting Power

You can also check for a failed fuel injector by checking to make sure that they are receiving power.

  • In order to conduct this method, turn your car’s ignition key on, but do not start the engine.
  • This will turn the car’s electrical system on, but we don’t want the engine to be running while conducting this test.
  • To conserve energy, turn off things that you don’t need to have running, such as the headlights and the radio.
  • Next, open your car’s hood and remove the covers on the battery’s terminals.
  • Connect a test light to the battery’s negative terminal (a test light is essentially a screwdriver with a light in it). If this is done correctly, the light inside the handle of the test light will illuminate.
  • Find the two wires that are connected to each injector.
  • One will be a 12-volt wire that should receive a constant supply of power from your battery.
  • Test each of the wires for voltage by using the sharp end of the test light and pressing it into the rubber coating that surrounds each wire until the sharp end punctures the wire itself.
  • One of those two wires should turn the test light on when it makes contact with the wire that is located within the protective coating.
  • If the test light illuminates when it touches one wire, the injector is working properly.
  • If the test light does not illuminate, the injector is failing.

Repeat the steps above with each fuel injector. If you come into contact with one that does not turn the test lamp on, take note of which injector it was so that you can address the issue later.


Assess the Injector Trigger Circuit

For this method of testing for a failed fuel injector, begin by connecting a test light to the positive terminal on your car’s battery.

  • Once connected, have someone turn the engine on.
  • Use the test light to check the opposite wire of each injector that was tested in the last method.
  • Push the sharp end of the test light firmly so that it pushes through the rubber coating until it connects with the metal wire housed inside.
  • Once contact is made, watch for a flickering light.
  • The test light should flicker a little. Have someone rev the engine for you if you can.
  • Doing so should cause the test light to flicker more brightly.
  • The illuminated light illustrates the signal that is being sent by the ECU to the injector essentially sending it a message that fuel should now be sprayed.
  • If the test light does not illuminate, there’s a good chance that the injector is failing.
  • Complete the steps listed above on all of the fuel injectors.
  • As each injector is connected to the test light, the intensity of the light should be the same.
  • If the light dims when an injector is connected, that signifies there is an issue with that injector.

Take note of it and continue testing each fuel injector.


How to Test Fuel Injectors – Conclusion

By using the information you gather from any of the three methods discussed above, you can determine whether or not you have a faulty fuel injector.

You can then either attempt to repair the bad injector yourself, or you can let a mechanic know which one is having issues so that he or she can repair it for you.


Do you know of another way to test your fuel injectors?  If so let us know below.

Here is another handy step-by-step guide, should you need it.

Wondering the best way to clean your fuel injectors?

Or check out our great new post on The TOP 10 Fuel Injector Cleaners here.

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