Fuel injectors have a solenoid that, when charged with electricity, opens a valve to allow pressurised fuel to be sprayed into the cylinder. Inadequate electricity, due to failure of the incoming lead or the fuel injector, will result in improper firing of the injector. Proper fuel injection also requires a specific range of fuel pressure to function properly. To test your fuel injectors, check the valve operation, the incoming voltage, the Ohms -- electrical resistance -- in the fuel injector and the fuel pressure regulator. Inadequate performance not due to part failure should be addressed with fuel injection cleaning.
Turn on the engine.
Place a stethoscope on the fuel injector and listen to the firing. A properly firing injector will click each time the solenoid engages the valve. You may also use a long screwdriver to check for the click. Place the screwdriver's metal tip against the top of the injector then place the side of your head, near your ear, against the handle of the screwdriver. The clicking sound will audibly transfer through the screwdriver.
Replace the injector if the solenoid operation is not present.
Turn the vehicle to the "On" position. It is not necessary to start the engine.
Remove the electronics plug from the fuel injector.
Insert the leads of a multimeter, set to measure volts, into each side of the injector plug. Measure the incoming voltage. The voltage should be approximately 12-volts.
Replace the injector if the test is positive -- leads are providing 12-volts -- but the injector is still failing.
Place the leads of a multimeter, set to measure Ohms, on each side of the injector plug terminals. Measures the Ohms.
Test the other fuel injector's Ohm reading. Compare them to the suspected injector. All fuel injectors should have the same, or very close, Ohm readings. Ohms measure resistance. Failure in the injector will allow too much or too little electrical resistance.
Replace the injector if the Ohm reading is too high or too low when compared to other injectors.
Remove the vacuum line to the fuel pressure regulator.
Look into the fuel pressure regulator. If fuel is present the pressure regulator diaphragm is ruptured.
Replace the fuel pressure regulator if the diaphragm is ruptured. Replace the hose is if the fuel pressure regulator is functional.
Remove all fuel injector electrical plugs.
Connect a multimeter, set to volts, to the failing or suspect plug. Connect the red lead to the plug. Connect the black lead to the positive terminal on the vehicle's battery.
Turn the engine over to charge the fuel injector electrical lines. An assistant may be required to engage the engine while you inspect the voltage. The voltage should alternate between 0-volts and 12-volts as the plug is engaged.
Connect another fuel injector plug. Recheck the voltage on the first plug. It is not necessary to check other plug connectors when searching for an electrical short. Continue attaching more plugs and retesting until all plugs are attached.
Replace the injector on any plug connected if the electricity fails on the tested plug. A fuel injector that is shorting will prevent electricity from firing in other plugs.
Fuel injectors which are operational but performing poorly should be cleaned or replaced. A fuel injector's moving parts will eventually wear out causing poor performance. For best results, replace injectors which are operational but still perform poorly when cleaned.