What type of Electronic Fuel Injection system fires only one injector at a time?

The type of Electronic Fuel Injection system that fires only one injector at a time is known as Sequential Fuel Injection (SFI) or Sequential Port Fuel Injection (SPFI).

Here are the steps of how it works:

1. The Engine Control Unit (ECU) receives information from various sensors located on the engine.
2. The ECU processes this information to determine the exact amount of fuel each cylinder needs for the next engine cycle.
3. The ECU then sends a signal to each fuel injector individually, in the exact firing order of the engine.
4. Each fuel injector then sprays the precise amount of fuel into its corresponding cylinder just before the intake valve opens, allowing the fuel to enter the combustion chamber.
5. This process repeats for each cylinder in a specific firing sequence, which is why it's called "sequential".

This system is more efficient and provides better fuel economy and performance compared to other types of fuel injection systems.