A vehicle's injectors are designed to spray fuel into the engine's cylinders, where it combines with air and is compressed before being ignited by the spark plug to produce power. If there is a problem with one of the fuel injectors, the engine is likely to malfunction or even stop running. There are a number of problems that can cause injector failure. Although some may exceed the experience of most amateur mechanics, a malfunction can often be diagnosed with common hand tools.
Part 1 of 3: Listen for bad fuel injectors
Step 1. Put on the proper safety gear
Before starting an automotive project, you must take steps to avoid injury. Eye protection (like safety glasses) prevents debris from falling or getting into your eyes while you work. You should choose a protection for your eyes that fits comfortably and does not interfere with your vision. Gloves are an optional addition to the safety equipment required for this task.
- Gloves can protect your hands from sharp objects while working in the engine compartment.
- You need to wear eye protection for this project.
Step 2. Open the hood and locate the fuel injectors
The easiest way to locate the injectors for a specific vehicle is by consulting the service manual. Most applications have a fuel injector for each cylinder. They are usually located on the intake manifold and are connected to each other with an injection ramp.
- The injection rail is a cylindrical rail that runs through the top of the intake manifold. Each fuel injector sits between these two items.
- V-style engines (V6, V8, V10) have two injection ramps with half the injectors on each side of the engine.
Step 3. Find a long metal rod or screwdriver
Locate a thin piece of metal that is at least 1 foot (30 cm) long. This piece should be made mostly of metal, but you can choose to use a screwdriver (even if it has a plastic or rubber handle).
- Make sure the piece you choose is at least 1 foot (30 cm) long, but no more than 2 feet (½ m).
- A long screwdriver or a thin piece of rebar can also work.
Step 4. Place the tip of the dipstick into a fuel injector
You are going to use the metal rod to transmit the sound of the injector to your ear without having to bring your face too close to the running engine. Place one end of the rod or screwdriver over the injector while supporting it with one hand.
Make sure to hold the screwdriver or metal rod at an angle that allows you to bring your ear closer
Step 5. Bring your ear close to the wand to detect a click
Angle your ear near the end of the metal rod or screwdriver in front of the injector. While the engine is running, you should hear an audible click from the injector. This sound indicates that the injector is activating.
- You must be very careful when tilting your head towards the engine compartment and make sure to keep your eyes open while listening to the dipstick to avoid accidental injury.
- If you have long hair, it should be tied tightly to prevent it from getting caught between the moving parts under the hood.
Step 6. Repeat these steps for each injector
Use the same method to check each fuel injector on your vehicle. If you spot one that doesn't click, then there is a problem with the injector or the electronic control that is transmitting to the injector.
- If you have an OBD2 scanner and the engine trouble warning light comes on, you can check to see if an error has occurred in the vehicle's computer regarding that cylinder or injector.
- Replacing this injector may solve the problem, but a professional mechanic will also likely need to diagnose your vehicle's electronic control unit and fuel system.
Part 2 of 3: Make sure the injectors are getting power
Step 1. Turn the key to the "on" position without starting the engine
To perform this test, the vehicle's electrical system must be activated without the engine running. Insert the key and turn it until the electrical system comes on, but stop before starting the engine. This procedure should activate all electronic components in the vehicle (eg interior lighting and radio).
- If you accidentally start the vehicle, simply turn it off and try again.
- The vehicle's battery supplies electricity during this test, so you should turn off things like the headlights and stereos to save power and make sure you have enough to start the vehicle later.
Step 2. Connect a test lamp to the negative terminal of the battery
This lamp looks like a screwdriver with a pointed end and a cord hanging from the handle. When the handle wire and pointed end come into contact with a full, powered circuit, a light bulb lights up inside the lamp handle. The cord that runs from the handle features an alligator clip on the end. Connect this clamp to the negative terminal of the vehicle's battery.
- You can look for the negative symbol (-) or the letters NEG to identify the negative battery terminal.
- Make sure the clasp has good galvanic contact for the test lamp to work.
Step 3. Locate the two wires that go into each injector
Each fuel injector has a metal clip connected to two wires coming out of it. One of those two wires is a constant 12-volt that must be continuously powered by the vehicle's electrical system. There should be a small exposed section of each wire coming out of the plastic clip that connects to the injector.
- These cables are often gray and black, but they can come in a variety of colors.
- These wires will be the only ones coming from each injector.
Step 4. Test each wire for voltage
Take the sharp end of the test lamp and press it firmly into the rubber coating around each wire until it penetrates the metal wiring. One of the two wires should cause the lamp to turn on when it comes in contact with the inside of the protective coating. If the test lamp is lit by a wire, then the injector receives the necessary constant voltage.
- Make sure to wrap a piece of electrical tape around any hole in the wiring harness that is large enough for you to see.
- If neither wire causes the light to come on, then there is a problem with the power going to the fuel injector, which will cause it to not fire.
- If all the wires that light up are a certain color, you should take note of the wires that are constant.
Step 5. Repeat the process for each injector
Test every wire coming out of the fuel injectors in your vehicle. If you locate an injector with a power problem, that does not mean that others do not have the same problem. Once you identify an injector with a power problem, you should write down what it was and continue testing the rest.
- Follow the wires from the injectors that do not connect to the test lamp to make sure there are no breaks in the wire that are preventing electricity from reaching it.
- Let your mechanic know that you were able to identify the injector with a feeding problem. The vehicle's electronic control unit may need to be replaced.
Part 3 of 3: Checking the Firing Circuit for the Injectors
Step 1. Connect the test lamp to the positive terminal of the battery
Take the same lamp that you used for the previous test, but this time connect the alligator clip to the positive terminal of the battery instead of the negative.
- You can look for the positive sign (+) or the letters POS on the battery to identify the positive terminal.
- Make sure the alligator clip has a safe galvanic contact or the test lamp will not work.
Step 2. Ask a friend to start or flip the engine
Have a friend start the engine. If the vehicle is not running, have your friend try turning it over while testing each injector. Make sure that no part of your clothing or body hangs over the engine compartment while you turn it on or turn it on.
If the engine won't start, remember that you can drain the battery and damage the engine if you try to crank it too long. Just try turning it over with the test lamp in place
Step 3. Test the opposite wire with the test lamp
Use the lamp and check the opposite wire of the constants you identified in the previous test. Firmly press the sharp end of the sensor through the rubber coating until it contacts the metal wire inside.
- Be careful not to go all the way through the cable with the sensor.
- You should always cover the holes in the cable's protective sheathing with electrical tape once you're done.
Step 4. Detect flashing or flashing lights
With the engine idling, the test lamp should blink faintly. When your helper presses the accelerator pedal, the light should blink brighter. This light represents the signal transmitted by the engine control unit to the injector to spray fuel. If the test lamp does not light, the injector is probably bad or there could be a problem with the vehicle's electronic control unit.
- This problem can be caused by a malfunction in the engine control unit, or a faulty injector along the injection rail.
- The electrical impulse is transmitted through each of the injectors to each other, so a bad injector could cause problems in multiple injectors.
Step 5. Disconnect the wiring clips to each injector and start the test again
Without connecting any of the injectors, the flashing pulse should be transmitted through all the wires without any problem. Use the test lamp to confirm this detail on the wire of the last fuel injector clip (at the end of the injection rail). Keep the test lamp connected as you reconnect each injector one by one. As you connect each injector, the intensity of the pulse should stay the same. This should not change until you connect a bad injector that generates too much resistance for the pulse to travel easily.
- If the pulsing light dims when one of the injectors is connected, then that injector is faulty and needs to be replaced.
- You can get new fuel injectors for your vehicle at most auto parts stores.