How To Test For Defective Vehicle Fuel Injectors

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How To Test For Defective Vehicle Fuel Injectors

6 July 2017
 Categories: , Blog


A rough idle, engine misfire or hesitation are common signs your fuel injector could be failing. The fuel injector sends fuel into the engine's cylinders converting it into a fine mist, similar to a hose nozzle.

The air mixes with the fuel in the manifold or port passes through the combustion chamber, then the spark plug ignites it. Before you take the vehicle to a mechanic, try to diagnose the issue yourself following these tips:

Do the Listening Test

To perform this test, you need work gloves, eye goggles, and a long screwdriver or metal rod. You may prefer to tie long hair back. 

Prop the hood open, and identify the fuel injector, which is commonly located between a  cylinder-shaped rail. V-style engines have two fuel injectors split between the engine.

Start the motor, if it isn't running, and lay the tip of the rod or screwdriver on the injector at a comfortable hearing distance angle. This helps you listen without needing to get your face to close to the injector. Lean close to the other end of the rod or screwdriver; keeping your eyes open. 

An audible constant clicking indicates the injector is good. Repeat the test for additional injectors, and proceed to the next test, if nothing seems wrong.

Test the Negative Wire for Power

Check the power of the injectors with a test light, a device that resembles a screwdriver. Turn the key "ON", but don't start the engine, so the system has power with the motor off. Look for the negative terminal on the battery, which should be marked "NEG", and find the two injector wires. Inspect the wires for charring and all wire terminals for rust.

Hook the test light clip to the negative battery cable, which is commonly labeled with a minus sign, and touch sharp end to each of the injector wires on the coating. The test light will slightly penetrate the wire coating.  

Observe whether one or both wires light the tester. If no wire lights the tester, the issue points to the amount of power entering the fuel injector. 

Check the Trigger Circuit

Repeat the light test; connecting the light to the positive terminal clip, which should be marked with a plus sign. Start the engine, and get an assistant to push the gas pedal while you do the test.

The light should produce a bright flicker as the assistant presses the pedal, then dim when they idle the vehicle. Test each injector. If the light dims, it indicates a defective injector. Seal small holes with silicone rubber or electrical tape.

Contact an auto repair​ company for more information and assistance.