5 Ways To Test Fuel Injectors

A fuel injector is a device used to fill in fuel into a car’s combustion chamber. This device, at times, may develop issues, and these issues may indicate that there’s are faults within the car engine. There are specific tools you’ll need to detect a faulty fuel injector. Below are five ways you can test your fuel injector.

How to Test Fuel Injectors

1. Run a test on the TBI Injector

You can physically check out the fuel spray on your TBI Injector. Checking the fuel spray is easy to do and makes issue detection faster. Typically, you’ll be needing an assistant to help you run this test. Below are steps to take when inspecting your fuel spray;

  • First, Take off the cover of the air cleaner 
  • Instruct your assistant to start the engine
  • Access the spray pattern that emerges from the Injector.

The fuel given off by the fuel spray should come out partially atomised in an inverted”V” pattern. An Erratic pattern presents the need for the fuel injector to be cleaned or the possibility of a broken internal component.

You can add a cleaning agent into the fuel tank, which would try to reset the faulty spray pattern. You can take your car to a mechanic if you feel you cannot handle the cleaning.

If, on the other hand, you don’t see any fuel pouring out, there could be several reasons:

  • Clogged Fuel Injector 
  • Injector failure
  • The Injector isn’t getting any electricity.
  • Faulty fuel pressure regulator 
  • Clogged fuel filter
  • Faulty fuel pump

2. Run a test on the EFI Injector

Compared to the TBI injectors, the area to access the fuel spray is unavailable. These Injectors typically have a Fuel rail assembly that keeps them in place, and tampering with them may ruin the entire system. Consequently, it isn’t easy to inspect the spray patterns of each Injector without the right tools.

There are several easy tests that you can use to reveal the fully functional injectors in your EFI system and whether the issue is with the Injector or the control unit.

You’ll listen to each Injector to see if it’s operating during this test. Injector valves make a clicking sound as they open and close. Follow these steps below to run a test on your EFI Injector;

  • Use a long screwdriver to listen to the injector sounds.
  • Startup the engine and let it stay idle for a few minutes.
  • Open the hood by putting the parking brake on.
  • Assemble your tools and place them on your ears and the side of the Injector. Place the end of the handle of a long screwdriver against your ear if you’re using a long screwdriver to access the Injector’s body.
  • There is a clicking sound when the Injector opens and shuts. When the solenoid in the Injector is activated and deactivated, the sound is heard. Listen for a clicking sound to determine whether the solenoid or the computer isn’t transmitting the pulse signal. If the computer is not transmitting the pulse signal, it meand  you’ve got a faulty injector on your hands.
  • Each Injector should be tested in this manner, and You should note dead injectors for testing purposes in the following section.

3. Run a Test on the Dead Injector

Two things are needed, a multimeter and the resistance value of your injector coil. You can find the resistance value of your injector coil in the service manual of your car. If the Service manual is unavailable, do well to purchase a repair manual from an auto parts store in your neighbourhood or online if necessary. 

Disconnect the electrical connector of your Injector while the engine is switched off. Regarding the resistance characteristics, set your digital multimeter to the value that best suits your fuel injector.

If you get a resistance reading that differs from what your service manual says, you’ll need to replace the Injector. Consider the following scenario:

  • The coil in the Injector is open if your meter reports infinite resistance.
  • The coil is half-open if your reading jumps all over the place.
  • The coil is shorted if the resistance reading is zero.

Run a Check on your Injector’s controlling circuit

Using a test light, You can Check the Injector Controlling Circuit. Follow the steps below:

  • Do well to safeguard the test light clip to a bolt-on the engine before startup.
  • Ensure you unplug the fuel injector you want to test from the electrical connector.
  • Switch the Car’s Ignition switch to the “ON” position.
  • Check each connector terminal using the test light. In the course of checking, one of the connections should radiate light, showing the computer’s power supply for the Injector.
  • A failure in the test light indicates a problem. Find a short, blown a fuse or broken connection anywhere along the circuit that includes your computer.
  • Once you’ve reconnected everything to the Injector, you’re ready to wire up the tester.
  • Start the engine with the help of an assistant.
  • Probe the other wire on the fuel injector connector from the other direction (the pulse signal coming from the computer). You should back probe the wire if you cannot push a pin through the wire and use the pin as a probe.
  • The test light will flash this time to indicate that injectors are getting pulse signals from the computer.
  • Replace the Injector if the power and pulse signals are present and the Injector is dead.
  • If the test light remains illuminated, the computer’s device driver may have failed, or the circuit may be faulty. If additional tests are required, consult your maintenance manual.

Another way you can check your injectors controlling circuit is to use a Noid light.  Using a noid light is the most straightforward method of testing an injector feeding circuit.

The noid light is connected to the fuel injector harness that you want to test. If you’re looking to get noid lights, go over to your local car parts store to purchase them, you might as well borrow and repay later.

Just make sure the package you borrow or buy includes the noid light you require for your vehicle’s make and model. Follow the tool’s instructions carefully.

4. Run a test on your Injector circuit’s power

Turn the key to the on position and connect a test light to the negative terminal to test the battery. Probe each side with a test light to see whether one of the wires on the injector connections is connected to 12 volts.

You should check the fuel injector fuse in PDC if no response is received from either wire. If the fuse is good, the wire can only be found and repaired using a fuel injection wiring diagram. Use silicone rubber to seal the test locations once testing is complete.

5. Run a test on your Injector Ground Trigger

The PCM shuts the injector circuit to activate the Injector. A test light is the best way to see the pulse produced by the PCM. With the help of a friend, connect the test light lead to the positive side of the battery and start or crank the engine.

On the opposite side of the injector connector from the power circuit, you should observe the test light flickering in response to engine RPM/Load.

If there is no pulse when the engine is running, suspect a broken wire connection or a failing PCM injector driver, which will necessitate a PCM replacement. Unplug all injectors and re-test the signal if a shorted injector prevents the injector driver from operating for additional injectors. 

If the pulse returns, replace the shorted Injector by plugging the injectors back in one at a time until the pulse fails. If the engine isn’t functioning, check the crankshaft angle sensor, which the computer uses to open the injectors (Note: A failed crankshaft angle sensor will not set a trouble code in most cases).


Your vehicle’s fuel injectors are designed to spray fuel into your engine’s cylinders, where it is mixed with air and compressed before being ignited by the spark plug to produce power. As a result, a problem with one of your fuel injectors could cause your engine to run poorly or not at all.

If you haven’t gotten a negative result after performing all of the tests, that doesn’t mean your injectors aren’t working correctly. You checked for some common problems that you can fix at home, but one or more injectors could have a faulty or broken return spring or a worn or dirty (less common) valve, causing the Injector to leak or block fuel.

Without the proper equipment, investigating some of these concerns might be difficult. However, a vehicle repair business with professional instruments can assist you in dealing with these situations.

So remember to follow the steps on how to test fuel injectors step by step, and you’ll be able to figure out what’s wrong with your car. Another option is to take your automobile to a mechanic, who will assist you.

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