The definition of a rule is  an official regulation, code of regulations or set practice. An example of a rule is that a red light means stop. An example of a rule is an employer demanding their employees arrive at 8am.
New injectors cost anywhere from $80-$120 apiece, making their replacement a somewhat pricey endeavor. There are three types of injector leaks-it can leak fuel into the manifold from the nozzle, it can leak fuel into the engine compartment from the fuel rail, and it can leak air (vacuum leak) from the manifold.
The fuel injector is the main actuator in a modern fuel injection systems. It is responsible for supplying the engine with fuel for combustion. In order to obtain the near perfect air/fuel ratio in todays engines, the injector must meter and deliver a precise amount of fuel into the intake runners.