Fuel injectors are connected to pressurised fuel lines. An electric pulse triggers a solenoid that opens the fuel injector's valve. Fuel then passes through the valve into the nozzle where it is sprayed in a fine mist into the combustion chamber. The pulsing of the fuel injector is triggered by the incoming electrical line, the solenoid and the operation of the valve. When a fuel injector pulse is interrupted, the injection of the fuel may become erratic or inhibited.
Start the vehicle's engine and allow the engine to idle.
Press the tip of a long-handled screwdriver to the exposed top of the fuel injector.
Press your ear against the handle of the screwdriver while it is touching the injector. Listen for a clicking sound. The clicking indicates the solenoid is engaging.
Remove the electrical plugs from the injectors you wish to test.
Turn the ignition key to the "on" position. Do not start the engine.
Disconnect the fuel injector plug. Move the plug into a position in which you can insert the multimeter leads into the plug connection.
Set the multimeter to measure volts. Touch the red and black leads to each side of the fuel injector electrical plug. It is necessary to have both leads touching the plug; you can place the leads on either side.
Read the multimeter voltage measure. The plug should be providing approximately 12 volts. This indicates the power to the fuel injector is present.
Remove all fuel injector electrical plugs from the fuel injectors.
Set the multimeter to measure volts. Hold the black multimeter lead against the positive terminal of the vehicle's battery. Insert the red multimeter lead into a fuel injector plug. It does not matter which plug you initially test.
Turn the ignition key to start the engine. An assistant may be required as you test the fuel injectors. As the engine turns over, monitor the voltage current displayed on the multimeter. The voltage should alternate between 12 volts and 0 volts. The alternating measurements indicate the electrical pulse to the fuel injector is present.
Connect a different fuel injector plug to the respective fuel injector. Retest the original plug. This test will indicate if the newly connected fuel injector has an electrical short. If the fuel injector is failing, the voltage on the first plug will not alternate between 12 volts and 0 volts. Leave the fuel injector plug connected.
Repeat step 4 until all the fuel injector plugs, except the original plug used in testing, have been connected. Replace any injectors which have electrical shorts.
Connect the final plug to the respective fuel injector. Disconnect one of the previously connected fuel injector plugs. Perform the test on the final plug. If the test fails, replace the last connected fuel injector.
Fuel injectors which are correctly pulsing but providing poor fuel injection may be dirty or worn. Dirty injectors may be cleaned professionally, or by using fuel additives. Poorly performing fuel injectors which do not respond to fuel injection cleaning should be replaced.