How to Check a Fuel Injector

READ COMPLETELY BEFORE BEGINNING:
Check for Fuel Injector Malfunction. When a fuel injector malfunctions it can allow excess or no fuel into the engine. The fuel injector is manufactured with a control valve that allows fuel to flow at prescribed amounts. If this valve sticks open it will flood the cylinder with fuel. If the valve sticks closed no fuel is allowed into the engine cylinder. Excess fuel causes black smoke from the exhaust. On the flip side if the injector is stuck closed the absence of fuel will cause the cylinder to go lean effectively fooling the oxygen sensor and causing the system to allow too much fuel into the engine through the remaining fuel injectors. Injectors can malfunction at anytime without warning. Using a few basic tests you can determine if one or more fuel injectors have failed causing the engine run-ability problem.



Fuel Injector

• While an engine is running you should be able to hear each injector clicking as the electronic valve opens and closes. To aid in this inspection use a stethoscope and touch it against each injector.
   
•  Remove the injector electrical connector, turn the key to the on position without starting the engine. This test will tell you if the computer has proper system voltage and injector trigger signal. Remove an electrical connector from a fuel injector. Probe both sides of the connector with a grounded test light or multimeter (voltmeter). Set the voltmeter to DC voltage. Have a helper turn the key to the "on" position without cranking the engine and observe. The test light/voltmeter should illuminate/read one side of the connector. The multimeter should read about 12 volts. Next, switch the test light or multimeter (voltmeter) lead (black) or to the positive side of the battery to test the system ground injector trigger. Disable the ignition system so the engine will not start (disconnect ignition coil or remove the ignition fuse). Probe the side of the connector that did not light up in the previous step, have a helper crank the engine over and observe the test light, it should blink on and off or the multimeter (voltmeter) should bounce from 0 to 12  volts. (Note: if no injector pulse is present try disconnecting the remainder of injectors and re-test, if a fuel injector is shorted it can shut down the injector driver causing no injector pulse. If injector pulse returns plug the injectors in one at a time until the pulse fails. Replace effecting injector). If this test is positive and the injector still will not operate the injector has failed and replacement is required.
  
• While the injector wire connector is off, test the fuel injector windings by setting the multimeter (voltmeter) to ohms and attach the leads to either side of the injector. Your reading will vary depending on manufacturer. For the exact ohms reading a car repair manual is needed. Test all of your injectors; if one injector reading is considerably different from the others replace the different injector.
  
• Check the fuel pressure regulator, remove the vacuum line feeding the fuel pressure regulator, check for the presence of fuel, if fuel is present the diaphragm inside the regulator has ruptured and is feeding raw fuel into the engine causing it to run rough.

Common Problems:

• A fuel injector is subject to high temperatures that can cause the injector to short circuit. Each injector has specific ohms of resistance reading that can be tested. This ohms reading can be found in a car repair manual. Temperature will cause readings to vary slightly. Injectors should be tested hot and cold. This is necessary because the heat or cold can create a condition that can short circuit the injector.
   
• Moisture can cause the injector connection to short circuit. Always inspect and clean all electrical connections at the fuel injector.