Many fuel injectors are designed to last the lifetime of the vehicle. However, they do occasionally fail. You can test your fuel injectors at home with a few methods, including using a metal rod to listen for the injectors’ characteristic clicking and a multimeter to test the resistance.

Modern vehicles that use fossil fuels—i.e., gas or diesel-fueled cars without carburetors—are powered by fuel-injected engines. These motors are more efficient than those with carburetors and use special injectors to release a precise amount of fuel into the engine’s cylinders. Testing your own fuel injectors can save you some cash, but there are a few things you should know first.

If you want to know how to test your fuel injectors or learn more about your car’s fuel delivery system, you’ve come to the right place.

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How to test fuel injectors

Your fuel injectors might malfunction if they become clogged with dirt or if an electrical connection is faulty.

You can take your vehicle to an auto repair shop to have them tested, but this service could be costly. Luckily, you can use a few DIY methods to test fuel injectors at home.

Before we get into the methods you can use to test your injectors, it’s helpful to note that if you don’t have any of the necessary tools, you can almost always borrow them from an auto parts store for a small fee—and sometimes, even for free!

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Listen for clicking sounds

This first method is simple and straightforward—and you might already have the right tool.

First, gather your tools. You’ll need a long screwdriver or a mechanic’s stethoscope. Alternatively, you can use almost any long, thin piece of metal.

Start your car and let it idle. Next, you’ll need to open the hood and locate the fuel injectors. You can usually find your car’s fuel injectors on its intake manifold.

The injectors are generally connected via a fuel rail, which looks like a long tube. There will be one injector per cylinder, typically with black plastic housing.

Place the tip of your screwdriver or stethoscope on the injector. If you’re using a screwdriver, put the handle against your ear. Listen for a regular clicking noise—that’s the sound of your injector opening and closing to release fuel into the engine.

Use this method to check each injector. If you don’t hear the clicking sound, that means the injector is dead, and either the solenoid inside the injector is bad, or your car’s computer is failing to send a signal to the injector.

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Take a resistance reading with a multimeter

Before beginning this fuel injector test, you’ll need to check your car’s repair manual for the injector resistance value. You can often find service manuals for your make and model at your local auto parts store or online.

With your vehicle turned off, locate the fuel injectors and unplug the electrical connector. Set your multimeter to ohms and probe the connector. If the resistance reading is different than what your vehicle repair manual defines, the injector needs to be replaced.

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Check the injector circuit power with a test light

For this final method, you’ll need a test light, a cheap tool that you can purchase at any auto parts or home improvement store.

When you’re ready, turn your car’s key to the “on” position, open the hood, and connect your test light to your vehicle’s negative battery terminal.

Next, locate the fuel injectors and unplug the electrical connector. Use your tool to probe both sides of the connector. One side should cause the test light to illuminate.

If the test light does not illuminate, there is an electrical connection problem. First, check for a blown fuse. If the fuses are in good condition, there’s most likely an issue with the connection somewhere between the PCM (your car’s computer)and the injector.

Plug the connector back in and connect your test light to your battery’s positive terminal. Have a friend or helper crank the engine and back probe the wire on the opposite side of the injector connector.

This should cause the light to flash, which means the computer is sending the injector the signal to open and close.

If both parts of this test caused your light to illuminate, simply replace the dead injector. If the flashing light does not appear, then there’s either a wiring problem or your car’s computer may need to be replaced.

Key Takeaway You can test your fuel injectors by listening for their clicking, taking a resistance reading with a multimeter, or checking the circuit power with a test light.

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Types of fuel injectors

When it comes to modern vehicles, there are four main types of fuel injection systems in use. All of these are known as electronic fuel injection (EFI) systems.

Single-point, also known as throttle body injection (TBI) systems, are the most basic form of fuel injection. These systems replaced carbureted engines and usually have one or two fuel injectors in the throttle body.

In multipoint or port fuel injection (MPFI) systems, each cylinder has a fuel injector positioned outside its intake port. Although these— systems are more precise than TBI systems, each injector sprays fuel simultaneously. This means that the fuel spray is not synchronized to the pistons’ movement and is less efficient than other fuel injection systems.

Sequential fuel injection, also known as timed injection systems, are similar to MPFI systems. The difference is that the fuel spray is timed to match the cylinder’s opening, and each injector releases fuel individually.

The final type of fuel injection system is known as direct injection. These systems inject fuel directly into the combustion chamber, past the cylinder valve. Although more common in diesel engines, they are gaining in popularity in gas-powered vehicles, known as GDI (gasoline direct injection) systems.

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What causes a bad fuel injector?

A bad fuel injector can be the result of various things. Some of the most common causes of bad fuel injectors are:

Poor quality fuel. The primary cause of bad fuel injectors is using fuel that contains impurities or debris. These contaminants clog your injectors and stop them from releasing the precise amount of fuel into your engine’s cylinders.

Heat soak. Heat soak happens when fuel gets trapped in your injectors and evaporates. This results in a residue called olefins, which can clog your injectors.

Solenoid failure. The solenoid inside your injectors might fail if it has a short.

Engine blow-by. This occurs when oil and fuel are blown past your car’s pistons into the crankshaft. Typically, your car’s PCV (positive crankcase ventilation) system will filter this buildup out. But if the PCV system fails or your air filter doesn’t catch it, the residue could clog your injectors.

Broken or leaking injector. Sometimes the injectors themselves crack or leak. If this happens, they will not release the precise amount of fuel, and your engine will not perform properly.

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Symptoms of a bad fuel injector

Faulty fuel injectors can cause a variety of problems in your car. However, many engine problems can result in similar symptoms. To help you diagnose the issue, these are six of the most common symptoms of a bad fuel injector.

Decreased engine performance. Bad fuel injectors can cause poor engine performance. This happens because the injectors do not deliver the fuel and air mixture necessary for combustion.

Rough idle or engine stalling. Your engine might shake, idle roughly, or stall if your injectors go bad. You might even notice the RPMs jumping around.

Engine misfire. A clogged or faulty injector can cause your engine to misfire when it doesn’t receive the correct amount of fuel.

Poor fuel economy. If your fuel injectors leak or waste fuel, your gas mileage could plummet.

Check engine light is on. Many things can cause your car’s check engine light to turn on; however, there are specific codes—such as P0201—that indicate problems with your fuel injectors. You can use an OBDII scanner to check these codes; many auto parts stores will inspect them for free.

Fuel smell. A fuel smell coming from your car might indicate that one of your injectors is damaged or stuck open.

How to replace fuel injectors

If, after troubleshooting and confirming the problem, you want to replace your fuel injectors yourself, these are the tools you’ll need:

A new set of fuel injectors

A ratchet wrench and socket set

Pliers

Extra fuel injector seals (o-rings)

A flathead screwdriver

Towels

Latex gloves (these are optional but will keep the gas smell off your hands)

Once you gather your tools, follow the steps below.

Step 1: Ensure that your car’s engine is cool to the touch and disconnect the negative battery terminal.

Step 2: Remove the engine cover and any other plastic shields that are in the way.

Step 3: Disconnect the electrical injector connectors and any metal retaining clips.

Step 4: Use your ratchet and socket set to disconnect the fuel rail from the engine. Depending on your vehicle, you might also need to remove the intake manifold.

Step 5: Gently pull up the fuel rail to remove it from the injectors. Try to apply even pressure to the rail to avoid damaging it.

Step 6: Use your flathead screwdriver to gently pry up the injectors and remove them from the engine.

Step 7: Install o-rings on the new fuel injectors and push them into the intake ports on the engine.

Step 8: Reinstall the fuel rail by evenly tightening all of the mounting bolts.

Step 9: Reconnect all electrical and fuel line connections. If you had to remove the intake manifold, make sure you replace the old gasket with a new one.

Step 10: Replace all engine covers and shields and ensure that everything is tight and in its original location.

Once you complete these steps, turn the key to the “on” position. You should hear the fuel pump turn on as it begins to fill the fuel rail. When the pump stops, turn the ignition off and repeat this process three to four more times.

Check for any gas leaks before you start the engine. Be sure to visually inspect the fuel rail, as well as the bottom of your car, if possible. As a final step, test-drive your car to check for performance issues and gas smells.

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Finding affordable car insurance

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FAQs

How do I check my fuel injectors without starting the car?

If your car doesn’t start, it could be because of a bad fuel injector. However, you can still check the injectors even if the car won’t turn over.

If you have battery power, you can perform a resistance test with a multimeter and check the injector circuit power with a test light.

If your battery is dead, you can remove the injectors, visually inspect them for damage, and clean them.

How do I know if my fuel injectors aren’t working?

Bad fuel injectors can cause a variety of issues for your vehicle. Some of the most common signs of faulty fuel injectors are poor engine performance, rough engine idling, engine misfires, unsteady RPMs, and a check engine light.

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