You can check for a misfiring injector without a diagnostic tool, but you would be guessing as to whether the injector itself is malfunctioning, the computer is malfunctioning or the wiring between the computer and the injector is bad. However, the injector itself is usually the culprit -- it is either bad or dirty. The cheapest repair is to try to clean the injectors before replacing them.
Start the vehicle.
Pull the wiring harness connector apart on each injector. Listen for a change in the rpm of the engine.
Plug in the injector's wiring harness connector. If the rpm drops when you pull the injector wiring harness off, that injector is working. If the rpm or the sound of the engine does not change when you pull the wiring harness connector off and plug it in, there is a problem with that injector, its wiring or the computer.
Shut off the vehicle.
