How do you kmnow which injector is not working?

To determine which fuel injector is not working, you can perform a few diagnostic tests. One common method is to use a multimeter to check the resistance of each injector; a significant difference in resistance indicates a faulty injector. Additionally, you can use a stethoscope or a mechanic's stethoscope to listen for clicking sounds when the engine is running—if an injector is silent, it may be malfunctioning. Lastly, observing engine performance issues or using an OBD-II scanner to check for specific error codes can also help identify the problematic injector.