In a multi-port fuel injection system, each cylinder has its own fuel injector. The fuel injectors need fuel delivered to them at a certain pressure -- commonly 32 to 44 p.s.i., depending on the year, make and model of your vehicle. If the fuel pump is bad, all the injectors will seemingly malfunction, as there won't be enough pressure to keep the engine running properly. If the engine is misfiring, there is most likely a problem with one or more injectors or the injector circuits, if the ignition system is working properly.
Locate the wiring harness connectors for each fuel injector. Start the vehicle. Remove the wiring harness connector from each injector, one at a time.
Listen to the sound of the engine when you pull the wiring harness connector off each individual injector. If the engine speed suddenly slows or the engine runs rough, that injector is working. If there is no change in the sound of the engine, or if it does not run worse, then that injector is either bad or clogged.
Plug that injector back in, and repeat the procedure for the next injector.
Run fuel injection cleaner through the fuel injection system (injector cleaner kits are available at most auto parts stores -- follow the instructions for the brand you purchase), then repeat the test. If the engine runs poorly each time you pull a wiring harness connector off, you have corrected the problem. If not, there is a problem with the injector and it must be replaced.
