What is the purpose of a fuel injector?

first off, they are fuel injector cleaners, the fuel injector is inside your car, and is what helps start it and keep it going, they do however get dirty over time and this can lead to a loss MPG, so u just pour the bottle into your gas tank as it says and go for a nice little cruise so it can clean it out.

The throttle body is the mechanism that controls the volume of air metered into the intake system of the engine. Your throttle pedal (gas pedal) in most cases is connected to this device by way of hard linkage or by a cable. Some newer vehicles are connected by wire instead, thereby allowing the computer complete control of engine parameters. Fuel injector is just what it sounds like. The engine control computer dictates how long the fuel injector is turned on, metering the desired amount of fuel. If the engine needs a great deal of fuel for the present conditions, the computer holds the injector on for a longer period of time, allowing more fuel to flow. When less fuel is required, the injector is held on for a shorter period of time. Hope this clears things up a bit.

1. I have never seen a gas station that stocks fuel injectors for sale at the counter

2. To inject fuel

3. You maintain your vehicle as per factory reccomended maintenance.