Here are some reasons why you might want to change the injectors on a Cummins engine: 

1.   Reduced engine performance: Injectors that are worn or damaged can cause a loss of engine power and a decrease in fuel efficiency. This can result in poor engine performance, reduced acceleration, and an increase in exhaust emissions.

2.   Hard starting: Injectors that are worn or clogged can cause the engine to have a hard time starting or not start at all. This can be caused by a lack of fuel reaching the combustion chamber.

3.   Rough idling: Worn injectors can cause the engine to run roughly or shake during idling, which can lead to further engine damage.

4.   Increased fuel consumption: Injectors that are not functioning properly can cause the engine to consume more fuel than necessary, resulting in higher operating costs.

5.   Failed emissions test: If the injectors are not functioning properly, it can cause the engine to fail an emissions test. This can be caused by a lack of fuel reaching the combustion chamber or an incorrect fuel spray pattern.

6.   Maintenance: Over time, injectors can become clogged with deposits and other debris, leading to poor engine performance. Regular maintenance and replacement of the injectors can help prevent these issues.

In summary, injectors are a critical component of the engine’s fuel delivery system, and they need to be in good working order to ensure optimal engine performance and fuel efficiency. Regular maintenance and timely replacement of injectors can help prevent issues that may require injector replacement.