Regan Brown
Fuel injectors are designed to spray fuel into the cylinders of a vehicle's engine, where it is combined with air and compressed before being ignited by a spark plug to generate power. A faulty fuel injector can cause the engine to run poorly or even fail to run at all. To test a fuel injector, you can use a 9V battery, a correct harness for the injector, and an on/off switch. You will need to locate the two wires going into each injector, which will be the only wires coming from each injector and will typically be grey and black. One of these wires is a 12-volt constant that should be continuously receiving power. You can test each wire for voltage by using a test light to penetrate the rubber coating and make contact with the metal wiring inside. If neither wire makes the light turn on, there is an issue with the power reaching the fuel injector. It is important to note that you should not keep the injector energized for a prolonged period, and it should be done while it is in cleaning fluid. Additionally, you can use a pulse tool and a measuring device to test the flow rate of the injector.
| Characteristics | Values |
|---|---|
| Power Source | 9V battery, 12V 2A slow charger, 12V flashlight battery, car battery |
| Tools | Noid light, on/off switch, DVOM, test light, ohm meter, injector tester |
| Process | Locate wires, test for voltage, repeat for each injector, test spray pattern |
| Notes | Ensure injectors are not energised continuously, use cleaning fluid, check for dirt |
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What You'll Learn
Use a 9V battery to check for a click
A 9V battery is the preferred power source for testing fuel injectors. This is because, when installed and powered in the car, injectors see a bit less than battery voltage due to the way that semiconductors are used for the switching. In addition, they see rapid pulses in normal service rather than the continuous duty cycle that we apply during testing and cleaning. To protect the coil in the injector during testing, the 9V battery is "just right".
You can use a 9V battery, the correct harness for the injector, an on/off switch, and wire it up to test for a click. You can also solder up a small test setup with a copper sleeve the injector slides into and gets retained in a small c-channel. You can use a can of carb cleaner with a straw and nylon tubing to pressurize it and a 9V battery with a switch to control the injector coil.
If you don't hear a click, it could be that your hearing isn't good enough to hear the click. You can try using a screwdriver on the injectors to help you hear it better. You can also try using a stethoscope to listen for the click. If you still don't hear a click, you may have two sticking injectors. If you tag the negative terminal of the 9V a couple of times, you may be able to get it to unstick.
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Test wires for voltage
To test wires for voltage, you can use a multimeter, a non-contact voltage tester, or a test light.
Using a Multimeter
Turn on the multimeter and set it to measure voltage (V) under the alternating current (AC) setting. Modern multimeters have two probes, one red (positive) and one black (negative). Insert one probe into one of the vertical slots and the other into the other vertical slot. You can then test between an unknown wire and a ground by putting one probe in the central U-shaped hole in the nearest outlet and touching the other probe to the wire under test.
Using a Non-Contact Voltage Tester
A non-contact voltage tester can detect line-level voltage without needing to complete a circuit.
Using a Test Light
First, locate the two wires going into each injector. Each fuel injector will have a metal clip plugged into it with two wires coming out of it. One of those two wires is a 12-volt constant that should be continuously receiving power from your vehicle’s electrical system. There should be a small portion of each wire exposed coming out of the plastic clip that connects to the injector. These wires are often grey and black but can come in any number of colors. They will be the only wires coming from each injector.
Take the sharp end of the test light and press it firmly into the rubber coating around each wire until it penetrates into the metal wiring itself. Be careful not to press the probe all the way through the wire and out of the other side. One of the two wires should make the test light turn on when it comes into contact with the wire inside the protective coating. If the test light turns on with one wire, then the injector is receiving the necessary constant voltage. If neither wire makes the light turn on, then there is an issue with the power reaching the fuel injector, which will result in failing to fire.
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Test wires for breaks
To test wires for breaks, you can use a multimeter or an induction test pen.
If using a multimeter, first ensure there is no power going to the wire. Then, connect the multimeter to each end of the wire. If a full circuit is made and there are no issues, the multimeter will show a low reading. If the reading shows 'I', there is a break in the wire.
Alternatively, you can use an induction test pen, which can detect voltage and continuity. First, rule out that the cables around the breakpoint cable have no power. Then, connect the cable with the breakpoint to the live wire, and hold the test pen perpendicular to the wire. Press and hold the "Induction Breakpoint Test" button, and slowly move the pen forward along the wire. When the AC signal suddenly disappears, it means the breakpoint has been detected.
When testing fuel injectors, you will need to locate the two wires going into each injector. One of these wires should be a 12-volt constant that is continuously receiving power from the vehicle's electrical system. You can test each wire for voltage using a test light. Press the sharp end of the test light into the rubber coating around the wire until it penetrates the metal wiring. If the test light turns on, the injector is receiving the necessary constant voltage. If neither wire makes the light turn on, there is an issue with the power reaching the fuel injector.
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Use a DVOM to measure ohms
To test your fuel injectors, you will need a Digital Volt-Ohmmeter (DVOM) or a multimeter with an ohms setting. You can access the injectors in the engine or use the manual. You may need to remove a plastic shield to access the injectors.
Firstly, set the DVOM to measure ohms. If the meter doesn't auto-range, set it to the lowest range. Next, place the meter leads on the prongs inside the connector, ensuring they do not touch each other.
High impedance injectors are the most common in modern cars, ranging from 12 to 17 ohms. Low impedance injectors are found on high-performance and larger injectors, with a much lower resistance, typically around 2-5 ohms.
Repeat this process with all injectors, and they should all have a resistance within half an ohm of each other. Any significant difference indicates that the injector should be inspected to ensure it is firing correctly. You can find the correct resistance for your injectors by searching online or in your vehicle's repair guide.
If you are experiencing any difficulties, a certified technician can assist you with diagnosing the problem and replacing any faulty fuel injectors.
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Check the spray pattern
To check the spray pattern of a fuel injector, you will need to remove the injector. You can then attach a 12-volt power source to the injector and attach pressurised air to the inlet. You should see a light misting or a fine spray with a clear, atomised pattern. If you see a solid, single spray or an irregular pattern, it means your injector is dirty or a component has broken or worn out.
A dirty injector can be fixed by adding a high-quality cleaning fuel system additive to the fuel tank or by asking a garage to clean the system.
You can also check the spray pattern by ear. If the injector is working well, you will hear a clicking sound inside. This sound is made by the solenoid inside the injector activating and deactivating the injector's valve. If there is no clicking sound, the computer may not be sending a pulse signal, or the solenoid has broken.
The spray pattern inside a fuel injector is important. The spray needs to be directed into the combustion chamber at the correct angle and atomisation shape. Any issues with this could cause engine misfire.
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Frequently asked questions
You can test a fuel injector on a bench using a 9V battery, a correct harness for the injector, an on/off switch, and some wires. You will need to locate the two wires going into each injector. Each fuel injector will have a metal clip plugged into it with two wires coming out of it. One of the wires is a 12-volt constant that should be continuously receiving power from your vehicle’s electrical system. Test each wire for voltage using a test light. If neither wire makes the light turn on, there is an issue with the power reaching the fuel injector.
If the test light turns on with one wire, then the injector is receiving the necessary constant voltage. If the test light does not turn on with any of the wires, there is an issue with the power reaching the fuel injector.
If there is an issue with the power reaching the fuel injector, you should follow the wires on the injectors and check for any breaks in the wire that may be preventing electricity from reaching it.
If your engine is running rough, there may be an issue with your vehicle’s fuel delivery system. A faulty injector can cause one of your cylinders to not ignite fully, throwing the balance of the engine off at all speeds. This can also ruin fuel economy since all of the fuel may not be combusting.
To properly clean the inside of an injector, you need to reverse the flow. Apply fuel pressure to the other side of the injector and then fire the injector. Once you are done, repeat the process in the standard fuel flow direction.
Note: It is recommended to use less than 9V to pulse the injector.
