How do you tell which injector is bad in a 1999 7.3 powerstroke?

To identify a bad injector in a 1999 7.3 Powerstroke, you can conduct a buzz test using a scan tool or a manual method by listening for the clicking sound when the injectors are activated. Additionally, monitor engine performance for symptoms like rough idling, misfires, or excessive smoke. You can also perform a contribution test to measure each injector's performance; a significant deviation in one cylinder's contribution indicates a potential faulty injector. Lastly, inspecting for any fuel leaks or abnormal noise can also help pinpoint the issue.