The fuel injectors (4) are found where the intake air runners connect to the cylinder heads. The injectors are mounted there, and each has a fuel and electrical connection. There are two injectors on each side of the engine.
The injectors are the fuel delivery vehicles for the engine, atomizing the fuel for proper and efficient combustion.
The injectors are nothing more than solenoid valves. There is a valve that is held closed by spring pressure until the control unit sends an electrical signal to the injector, which travels through a winding, creating a magnetic field, which lifts the solenoid, allowing fuel to flow through the injector. The tip on the end of the injector helps to atomize the fuel in a cone-shaped spray.
The injectors are supplied with power all the time and are activated when the control unit grounds them. The amount of fuel injected is determined by the control unit through the length of time that the control unit holds the injectors open. The injectors are all activated by the control unit at the same time, not in a sequential manner. They are activated once every crankshaft revolution. The control unit gets this information from a wire that connects to the negative terminal on the ignition coil.
The fuel pressure also affects how much fuel is injected, however the control unit has no control over or knowledge of the fuel pressure. The fuel pressure is maintained by a purely mechanical device, the fuel pressure regulator.
The injectors can be tested for fuel leakage by removing them from the intake manifold (leaving the fuel and electrical connections intact) and operating the fuel pump, measuring how much fuel leaks in a specified time period.
The injectors can be tested for the proper spray pattern by removing them from the intake manifold (leaving the electrical and fuel connections intact) and running the starter briefly, making sure the spray pattern is an even cone shape. A bad spray pattern can cause rough running due to improper fuel atomization.
The electrical connections to the injectors can also be checked with a test lamp to make sure the injectors are getting power.