* Clogged injector. If the injector is clogged, it will not be able to allow the right amount of fuel to flow through, which can cause it to click.
* Electrical issues. If the injector is not getting the correct electrical signal, it will not be able to open and close properly, which can cause it to click.
* Damaged injector. If the injector is damaged, it will not be able to function properly, which can cause it to click.