The fuel injectors in your diesel engine are vital to the operation of your vehicle. When they function properly, you enjoy a smooth-running vehicle that gives you all the power you need for getting around and getting things done. When operating at peak performance, your fuel injectors get you the fuel efficiency you expect from your vehicle and help keep your engine’s emissions safe. In this article, we will teach you how to test your fuel injectors.


Your approach will depend on the type of fuel injection in your vehicle. If you have a throttle body injection (TBI) system, begin with these steps:

  1. Remove the air filter housing.
  2. Have someone else start the engine while you take a look.
  3. Look at the fuel spraying from each injector.
  4. If the fuel is partially atomized and spraying in a v-shaped pattern, that injector is fine.
  5. If the fuel spray is broken or solid, the injector is clogged. You can try to unclog it with a fuel cleaner additive or take it to your mechanic.
  6. If there is no fuel spraying from the injector, it could be completely clogged, a bad injector or something is wrong elsewhere like the fuel pump or fuel filter. If that’s the case, move to the next steps.


The next steps apply to a TBI system injector that is completely clogged or not functioning, as well as vehicles that utilize electronic fuel injection (EFI) systems. This is where that long screwdriver or metal rod comes in.

  1. Start the engine and place the end of the screwdriver on a fuel injector.
  2. Carefully lean your head toward the far end of the screwdriver or rod. Make sure you have your safety gear on. If the injector is activating properly, you should be able to hear a clicking sound.
  3. Repeat the screwdriver test on each injector and take note of each one that you can’t hear clicking.
  4. Turn off the engine and turn on the battery so the lights, radio, and other electronics are on but not the engine.
  5. Connect the clip of the automotive test light to the negative terminal of your vehicle’s battery. Then take the pointed tip of the test light and touch it to the small bit of exposed wire on the fuel injector connector. The test light should light up if the injector is functioning properly.
  6. Repeat the test light procedure for each injector, taking note of each one that does not light up.

What You’ll Need to Test Your Fuel Injectors

The tools you’ll need to test your fuel injectors are relatively simple, and you probably have most of them lying around in your house or garage. The list of items you’ll need to test fuel injectors includes:

  • Work gloves for safety
  • Protective eyewear
  • Long screwdriver or metal rod (about one foot in length)
  • Automotive test light

Use Your Senses

When things aren’t right with your fuel injectors:

  • You lose power
  • Emissions get worse
  • Your fuel efficiency tanks

This can be very frustrating, especially considering the thought you put into opting for a diesel engine.

While the prospect of testing your own fuel injectors can seem intimidating if you’ve never done it before, it’s actually a lot simpler than it seems. With our tips, you can quickly learn how to test fuel injectors in only 30 minutes.

Those tools are helpful and we’re going to use them, but the most important tools in testing fuel injectors are probably what you already carry around: your eyes and ears.

Knowing how to test fuel injectors is a fairly simple process that can help you diagnose any problems with your fuel injection system. There can be times, though, when all of your injectors pass the above tests and there still seems to be a problem with the system and your engine’s performance. In these instances, there could be something wrong with a peripheral system, or the injectors can appear alright but have something more subtle going on. In this case, you’ll want to take your vehicle to a mechanic for further testing.

Sometimes, fuel injection or peripheral issues can be hard to diagnose. The tests you already ran on your fuel injectors will help guide your mechanic’s diagnosis and save time while getting to the heart of the matter.

Make a Plan of Action

If you test each fuel injector and find one or more not working, you now know which injectors need to be cleaned or replaced. If you are comfortable removing them yourself, cleaning them is relatively straightforward.

Once you have removed an injector, spray it with an undiluted fuel system, throttle system, or carburetor cleaner to flush out any residue that is obstructing the injector. Once you have done this with each of the suspect injectors, you can replace them and test them again.

How to Prevent Future Fuel Injector Problems

If your injectors are bad, they will need to be replaced. The key is to replace them with the best fuel injectors you can buy, so you can get the reliable performance you need from your diesel engine. Buy Dieselogic fuel injectors to ensure:

  • High engine performance
  • Fuel efficiency
  • Cleaner emissions

Once you know how to test fuel injectors and have solved the problem, talk with your mechanic about the possible underlying causes. There are many factors that can cause injectors to fail, including major internal and external deposit buildups. Your mechanic can give you some tips on how to prevent buildups, such as using a fuel system cleaner. You might not need to add a system cleaner every time you fill up, but using it regularly can help keep your system clean and free of deposits.

Dieselogic Fuel Injectors for Peak Performance

These tips will help you test your fuel injectors and keep the engine efficient and clean. Your diesel vehicle will keep running the way you expect it to, so it won’t slow you down again. You will also be able to prevent loss of engine performance and even avoid more significant damage to your engine down the road.

Don’t mess around with inferior fuel injectors. Upgrade to Dieselogic fuel injectors for quality, and so that you’re getting the power and efficiency you expect from your diesel engine.