Rajan Wilcox
Fuel injectors are responsible for spraying fuel into the cylinders of an engine, where it is combined with air and compressed before being ignited by the spark plug to produce power. A faulty fuel injector can cause an engine to run poorly or even fail to run. To test a fuel injector pulse with a multimeter, you will need to set the multimeter to the Ohms scale according to the resistance specifications for your fuel injector (usually at least 30 Ohms). Then, with the vehicle turned off, disconnect the electrical connector for the fuel injector and use the multimeter to take a resistance reading. A good fuel injector should read between 10 and 18 Ohms. If your reading is jumping around or showing infinite or zero resistance, there may be an issue with the coil.
| Characteristics | Values |
|---|---|
| Testing tool | Multimeter, test light, screwdriver, mechanic's stethoscope |
| Multimeter setting | Ohms |
| Multimeter value | 10-18 ohms |
| Injector housing | Black plastic |
| Location | One per cylinder, typically installed directly above the cylinder |
| Injector signal | Controlled by PCM |
| Pulse signal | Transmitted through each injector |
| Faulty injector | Pulse intensity decreases, light dims |
| Dead injector | No clicking sound |
| Coil issues | Coil is partially opened, coil is shorted |
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What You'll Learn
Set multimeter to ohms to test resistance
To test a fuel injector pulse with a multimeter, you must first set the multimeter to ohms to test resistance. This will allow you to determine the condition of the fuel injector and whether it needs to be repaired or replaced.
A fuel injector is a vital component of an engine, responsible for spraying fuel into the cylinders, where it is combined with air and compressed before being ignited by the spark plug to generate power. Therefore, any issues with the fuel injector can cause the engine to malfunction or fail to run.
To test the fuel injector, you should first disconnect the electrical connector for the fuel injector with the vehicle turned off. Then, set the multimeter to the ohms range to test the resistance. The resistance value should be specified in your vehicle's service manual, and most fuel injectors should read between 10 and 18 ohms. If your injector is reading less than 10 ohms, it may be failing or faulty.
By following this procedure and comparing your resistance readings to the specified values, you can identify any faulty fuel injectors and take appropriate action, such as repairing or replacing them.
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Check for a pulse signal from the computer
To check for a pulse signal from the computer, you will need a test light or a digital multimeter. The test light is an inexpensive but efficient tool that can be used to check for power and pulse signals coming from the computer on each dead injector.
First, hook the test light clip to a bolt or bare metal bracket on the engine. Then, unplug the electrical connector from the fuel injector you want to test. Back probe the opposite wire on the fuel injector connector (this is the pulse signal coming from the computer). If you can't back probe the wire, insert a pin through the wire and use the pin to probe the wire. This time, the test light should flash, meaning the injector is receiving the pulse signal from the computer to open and close the injector.
If the test light remains lit, the device driver in the computer may have failed or there's a problem in the circuit. Check your repair manual for further tests, if necessary. You can also test the injector controlling circuit using a noid light, which is the easiest way to test an injector feeding circuit. The noid light connects to the harness of the fuel injector you want to test and can be loaned or bought from a local auto parts store.
If there is no clicking sound, either the computer is not sending the pulse signal or the solenoid has broken. This means you have a dead injector. Repeat the process on another injector and make a note of dead injectors, then you can test them. Checking the injector's coil is one test you can do on a dead injector. To do this test, you will need the resistance value for the coil inside the injector and a multimeter. You can find out the injector resistance value in the manual of your car.
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Observe the injector's valve and spray pattern
The valve and spray pattern is the most crucial aspect of testing a fuel injector. You can test the valve with the injector still installed using a fuel pressure gauge while hot-wiring the fuel pump to stay on. To do this, carefully attach a 12-volt power source (power and ground) to the injector. If the injector valve is functioning and not blocked, you should see the gauge fluctuate as you connect and disconnect the circuit.
To check the injector spray pattern, the injector must be removed. Attach pressurised air to the injector inlet, along with a 12-volt power and ground source to energize the injector. Compressed air should be released from the outlet valve, and traces of fuel should remain in the injector. It is important to take the usual fire precautions when performing this test.
The spray pattern of the fuel injector is important because it determines how the fuel is delivered into the engine. The spray pattern can vary, with some injectors having two holes, four holes, or even more. The number and arrangement of holes in the injector will modify the spray pattern. For example, a four-hole spray pattern is supposed to improve fuel economy and performance. The spray pattern can also be in the shape of a "V", with some patterns being wider or narrower than others.
It is important to note that the spray pattern should match the specific type of system in your vehicle. Changing the spray pattern may or may not result in an improvement in performance. For example, installing a wide "V"-shaped pattern that misses the intake valves may not work as well as the stock injector. Therefore, it is crucial to ensure that the spray pattern of the fuel injector matches the requirements of your vehicle's engine.
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Test the injector's coil
Testing the injector's coil requires a multimeter to take a resistance reading. Before you begin, ensure you are wearing protective gloves and eyewear for safety.
Firstly, turn off your vehicle and disconnect the electrical connector from the injector. You can then use a multimeter to take a resistance reading. The multimeter should be set to ohms/resistance mode. Check your vehicle's service manual or look online to find the correct value for your vehicle (most fuel injectors should read between 10 and 18 ohms).
When testing the coil, connect the positive (+) probe of the multimeter to terminal number 1 and the negative (-) probe to terminal number 2 of the coil connector. The meter should indicate infinite resistance. If the results are not as specified, the coil should be replaced.
You can also reverse the meter leads (negative probe to terminal 1 and positive probe to terminal 2) and the continuity should be indicated, but not zero ohms. If the results are not as specified, the coil should be replaced.
Additionally, you can connect the ohmmeter between the secondary terminal (where the spark plug connects) and terminal 1. The meter should indicate infinite resistance. If it does not, the coil should be replaced.
Note that using an ohmmeter to test coils may not be the most reliable method, and there are other methods to test the injectors.
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Use a test light to check for flickering
To test a fuel injector pulse with a multimeter, you can use a test light to check for flickering. This test light can be used to observe the pulse produced by the PCM (the computer that controls the fuel injector as part of the fuel injection system).
Firstly, ensure you are wearing protective gloves and eyewear. Fuel may be present during testing, so standard fire precautions apply. Next, with the key in the 'on' position, connect the test light to the positive side of the battery. Then, with the engine idling, probe the opposite side of the injector connector from the power circuit. The test light should now flicker dimly.
Ask your helper to apply throttle by pressing the gas pedal. As they do this, the light should flicker more brightly. This light represents the signal being transmitted by the ECU to the injector to spray fuel. If the test light is failing to light up, the injector may be faulty or there could be an issue with the electronic control unit.
If the engine is not running, check the crankshaft angle sensor, which the computer uses to open the injectors. A failed crankshaft angle sensor will not usually set a trouble code. You can also test the injector ground wire for continuity and excessive resistance.
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Frequently asked questions
With the vehicle off, disconnect the electrical connector for your fuel injector. Set your multimeter to the Ohms scale, with a value that's in line with the resistance specs for your fuel injector (usually at least 30 Ohms). Connect the multimeter leads to the terminals of the injector, the polarity of the leads does not matter. A reading of between 10 and 18 Ohms is standard, but check your vehicle's service manual for the correct value.
If your reading is jumping around, the coil is partially opened. If your meter reads infinite resistance, the coil is open. If you read zero resistance, the coil is shorted.
With the key in the 'on' position, use a test light connected to the negative side of the battery. Probe both sides of the injector wiring connector. One of the wires should react by registering around 12 volts on the meter or illuminating the test light. If the test light remains lit, there is a problem in the circuit.
