Ameer Randolph
The Power Probe IV is a diagnostic circuit tester that can be used to test fuel injectors. It comes with a range of features, including a colour LCD display, multi-meter functions, and advanced diagnostic test modes. The Power Probe IV can be used to test the trigger signal from the PCM, the power circuit, and the operation of the injector itself. It can also be used to test the fuel injector valve and spray pattern. To test the valve, a 12-volt power source can be attached to the injector, and the user should be able to see the gauge fluctuate as the circuit is connected and disconnected. The spray pattern can be observed by attaching pressurized air to the injector inlet and a 12-volt power source to energize the injector.
| Characteristics | Values |
|---|---|
| Purpose | To test fuel injectors |
| Tool | Power Probe IV |
| Display | Easy-to-read colour LCD display |
| Functionality | Multi-meter functions, advanced diagnostic test modes |
| Use | Connect to car battery for access to diagnostic functions |
| Testing | Test positive and negative wiring, voltage wires, fuse boxes, motors, lights, relays, sensors, wires, communications circuits, computers |
| Safety | Safely measure up to 70 VAC |
| Additional | Water and dust resistant |
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What You'll Learn
Using a Power Probe to test a fuel injector
The Power Probe IV is a diagnostic circuit tester that can be used to test a fuel injector. It comes with a range of features that make it a useful tool for automotive technicians, including an easy-to-read colour LCD display, powerful multi-meter functions, and advanced diagnostic test modes.
To test a fuel injector, the first step is to check the trigger (ground) signal from the PCM, the power circuit, and the operation of the injector itself. A test light or voltmeter can be used to test the injector signal from the computer. If using a voltmeter, check the resistance through the injector. As fuel may be present, take the usual fire precautions and wear protective gloves and eyewear.
With the key in the 'on' position, use a test light or voltmeter connected to the negative side of the battery. Gently 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.
To test the valve and spray pattern of the injector, carefully attach a 12-volt power (power and ground) source to the injector. If the injector valve is working and not plugged, you should see the gauge fluctuate as you connect and disconnect the circuit. To check the spray pattern, the injector must be removed. Attach pressurized air to the injector inlet and a 12-volt power and ground source to energize the injector. Compressed air should be released from the outlet valve with traces of fuel. Observe the pattern; it should be robust. If the pattern is muted, the injector should be replaced.
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Using a screwdriver to check for an audible clicking sound
To check for an audible clicking sound, start by popping the hood of your car while the engine is running. Place a thin metal rod or screwdriver on one of the injectors. You can use a standard screwdriver or a piece of thin hose of the appropriate length. Ensure that you hold the screwdriver at an angle that allows you to bring your ear close to the opposite end. As the engine runs, listen for an audible clicking sound, indicating that the injector is functioning. This sound originates from the solenoid inside the injector, activating and deactivating the injector's valve.
If you do not hear the clicking sound, it could mean that either the solenoid has failed or the computer is not sending the pulse signal, resulting in a dead injector. Repeat this test for each injector, noting any that are not clicking. These non-functioning injectors may have issues or problems with the electronic component that controls them.
It is important to take the necessary fire precautions when performing this test, as fuel may be present during the process. Always wear protective gloves and eyewear to ensure your safety.
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Using a voltmeter to check resistance
To check the resistance of a fuel injector with a voltmeter, you will need to perform an injector voltage supply test. This test requires an assistant and is an important safety step to prevent major engine damage.
First, remove the fuel pump fuse to prevent the car from starting while the crank test is being performed. This will also prevent large quantities of gasoline from being injected into the engine cylinders.
Next, connect the voltmeter leads to the terminals. The polarity of the leads is irrelevant. This test will give you a baseline ohm reading of all injectors, which should typically range between 11 and 14 ohms. It is important to note that fuel injectors should be tested cold unless otherwise specified, as temperature variances will change the readings. If the test shows high resistance or an open circuit, the injector needs replacement.
To test the injector circuit for ground, insert the ground voltmeter lead into the open slot of the connector if there is voltage present. Have your assistant crank the engine over, and observe the voltage reading. It should fluctuate as the ground signal is applied and then removed as the engine cranks over. If a digital meter is being used, the reading may be difficult to determine as the voltage drops to zero and then back. This indicates that the circuit is normal, and the ground signal is present. However, if there is no ground signal, the issue lies with the computer or related wiring.
Additionally, a quick test to check if the injector is operational is to use a mechanic's stethoscope. Touch it to the injector while the car is running and listen for a ticking sound.
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Testing the injector signal from the computer
Testing the injector signal from a car's computer can be done in several ways. One way is to use a test light, which is a screwdriver-like tool with a fine point and a wire hanging out of the handle. When the wire and the pointed end touch a complete and powered circuit, a light bulb inside the handle lights up. To test the injector signal, attach the alligator clip from the test light to the negative terminal of the vehicle's battery. Then, with the engine idling, probe the opposite side of the injector connector from the power circuit. The test light should flicker, indicating that the injector is functioning correctly. If the engine is running and the light does not flicker, it could be due to a bad wiring connection or a failed PCM injector driver.
Another method is to use a voltmeter to check the resistance through the injector. Set the voltmeter to ohms and connect the leads to the injector's electrical terminals. Most injector readings should range between 11 and 14 ohms. If the test shows high resistance or an open circuit, the injector may need to be replaced.
Additionally, the valve and spray pattern of the injector can be tested. This can be done with the injector still installed by attaching a 12-volt power source and ground to the injector. If the injector valve is working properly, the gauge should fluctuate as you connect and disconnect the circuit. To check the spray pattern, the injector must be removed, and pressurized air and a 12-volt power source attached. The compressed air released from the outlet valve should have traces of fuel, and the spray pattern should be robust. If the pattern is muted, the injector may need to be replaced.
Furthermore, if you have an OBDII scanner and your vehicle's check engine light is on, you can use it to check for any errors in the vehicle's computer related to the injector. This may indicate that the injector needs to be replaced or that a diagnostic of the vehicle's electronic control unit and fuel system is required.
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Using a test light to observe the pulse produced by the PCM
To test the injector signal from the computer, a test light works best. You will need safety gear like protective gloves and eyewear because fuel may be present during the testing process. Fire precautions are also necessary.
To use a test light to observe the pulse produced by the PCM, attach the test light lead to the positive side of the battery. Then, have a helper start or crank the engine. You should then probe the opposite side of the injector connector from the power circuit. If everything is functioning as it should, you should observe the test light flickering in response to the engine RPM/Load.
If the engine is running and no pulse is observed, you may be dealing with a bad wiring connection or a failed PCM injector driver. In this case, a PCM replacement may be warranted. A shorted injector can hinder the injector driver operation for additional injectors. To confirm this, unplug all injectors and re-test the signal. If the pulse returns, plug the injectors back in one at a time until the pulse fails. Then, replace the shorted injector.
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 set a trouble code in most cases.
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Frequently asked questions
The Power Probe IV is a car diagnostic test tool and the next generation of Power Probe Circuit Testers. It has multi-meter functions, advanced diagnostic test modes, a colour LCD display, and a water and dust-resistant housing.
First, carefully attach a 12-volt power source (power and ground) to the injector. If the injector valve is working, you should see the gauge fluctuate as you connect and disconnect the circuit.
To check the spray pattern, the injector must be removed. Attach pressurized air to the injector inlet and a 12-volt power and ground source to energize the injector. Compressed air should be released from the outlet valve with traces of fuel. Observe the pattern, which should be robust. If the pattern is muted, the injector should be replaced.
P-P mode can be used on any AC voltage signal where a Peak to Peak (P-P) voltage measurement is required. It displays the total voltage difference from the lowest to the highest voltage extreme on an AC signal.
Hz FRQ CTR mode is used for measuring the frequency of an alternating voltage signal. It displays the frequency in Hertz (cycles per second) and the Pulse Width in milliseconds.
