How to Test and Clean Fuel Injectors

mechanic fixing fuel injector

We all want the best mileage and performance from our vehicles, and one of the keys to an optimally functioning engine is a clean fuel injector. However, additives and hydrocarbons present in fuel can often leave gunk or buildup around the nozzle of the injector, causing poor fuel flow, ineffective atomization, and uneven distribution.

Ideally, you should be fueling your vehicle with a high-quality fuel that limits the amount of buildup in your injectors. However, even the most well-fueled injectors must be cleaned or replaced at some point.

Unlike many engine parts which require regular maintenance, there is no specific time or mileage that indicates when you need to clean your injectors. Fortunately, when your fuel injector is dirty, your vehicle has many ways to let you know that it is time to clean them.

Symptoms of a Dirty Fuel Injector

One of the first things you will notice is a significant reduction in power or acceleration. Reduced power is often due to an ineffective ratio of air to fuel, which can result from a clogged nozzle.

You may also notice a decrease in fuel efficiency as your engine uses more fuel to maintain the same level of performance. Stuttering and misfires can also indicate blocked injectors due to missed strokes.

These symptoms may not always result from dirty injectors. Other engine parts failing can also cause these problems. So, if you want to be certain that it is the injectors that need cleaning, you will need to perform a diagnostic test.

How to Test Your Injectors

Cleaning injectors can be a complex and laborious task, and, if you aren’t mechanically minded, you may damage important engine parts. Save yourself some time and trouble by performing a couple of simple tests before diving in.

To perform these tests, you will need a fuel pressure gauge, an injector tester, and a test light.

Check the Fuel Pump

  1. Locate your fuel pressure port along your fuel rail. Remove the plastic cap and attach the fuel pressure gauge with the correct adapter.
  2. Consult your car’s user manual to check the fuel pressure for your car’s make and model. This is usually between 50 and 60 Psi for most cars.
  3. Turn the key in the ignition to the ON position to prime the fuel pump.
  4. Observe the gauge reading to find the pressure of the fuel pump. Make sure to wait a couple of minutes for the pressure to stabilize before checking the final reading, as the pressure can oscillate.

Check if the Injectors Are Receiving Power

  1. Unfasten the connector for your fuel injector. The method for doing this will depend on your harness.
  2. Connect the test light to the negative terminal of the battery and apply the point of the test light to each of the two injector wires. The test light will light up with each one, indicating there is sufficient power going to the injector and, therefore, it is not faulty or damaged.
  3. Repeat this with each injector.

mechanic troubleshooting car engine

Check the Trigger Circuit

  1. Connect the test light to the positive terminal.
  2. Start the engine and leave it running.
  3. Test the opposite wire.
  4. Check for flashing or flickering, which indicates that the signal is being correctly transmitted to the ECM.
  5. Disconnect the wiring clips from the injectors and perform the test again; reconnect the wire with the test light attached to check that the flickering remains consistent.

If the injectors’ component and power supply are all functioning, the injectors are probably blocked and need cleaning.

How to Clean Fuel Injectors

If tests indicate the injectors are dirty, there are two methods to clean them. However, the easiest, most user-friendly, and often most successful method is to use a cleaning kit.

You will need an injector cleaning kit, air compressor, and fuel pump regulator.


Ensure the kit is compatible with your vehicle and the cleaning solvent is the correct one for the kit. Fill the kit canister with the solvent, and then connect the kit to the fuel port located on the fuel rail.

Disable the fuel pump, and either connect the return tube or a U-tube so that the fuel returns to the tank, and connect the fuel pressure regulator. Then check the fuel pump is inactive by turning over the ignition and opening the fuel cap to prevent pressure buildup.

Connect the compressed air hose and adjust the pressure according to the kit manual guidelines.

Start the car and let it run until all the solvent is gone from the canister.

Unless you are mechanically minded, other DIY methods of cleaning injectors are not recommended, as they can be dangerous and result in engine damage. If your injectors still don’t work after the cleaning kit, they are likely clogged and need professional cleaning.

closeup of car injection system

Final Thoughts

Testing and cleaning your fuel injectors in an important piece of maintenance for your vehicle’s engine—but, as always, prevention is better than cure. If you are not using premium fuel for your vehicle, it is advisable you periodically add a cleaner to your gas tank to prevent buildup from occurring.

If you continue to notice your car performs poorly, it is likely your injectors are worn and need replacing. The best course of action is to take the injectors to a mechanic for bench testing to determine the extent of the damage. Purchase durable, reliable fuel injectors to avoid any future performance problems.

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