Throttle Body Fuel Injection

Throttle body fuel injection (TBI), also known as single point injection (SPI), is a type of fuel injection system commonly used in older vehicles. Here’s how it works and some key characteristics:

1. Location of Injectors: In a throttle body fuel injection system, the fuel injectors are located within the throttle body assembly, which is mounted at the entrance of the intake manifold. This setup allows for the centralized delivery of fuel to multiple cylinders from a single point.
2. Operation: The throttle body serves as the primary air control device, regulating the airflow into the engine. Fuel is injected directly into the incoming air stream inside the throttle body, where it mixes with the incoming air before entering the intake manifold.
3. Simplified Design: TBI systems are relatively simple compared to multi-port fuel injection (MPFI) systems. They typically feature fewer components and require less complex fuel delivery systems. This simplicity can result in lower manufacturing costs and easier maintenance.
4. Single Point of Injection: Since fuel is injected at a single point within the throttle body, TBI systems have limited control over fuel distribution to individual cylinders compared to MPFI systems. This can result in less precise fuel metering and potentially uneven fuel distribution among cylinders.
5. Throttle Body: The throttle body assembly contains the throttle plate, which is controlled by the accelerator pedal. As the throttle plate opens and closes, it regulates the airflow into the engine, and the fuel injectors deliver the appropriate amount of fuel based on engine demand.
6. Fuel Delivery: Fuel delivery in TBI systems is typically controlled by an electronic fuel injector, which is operated by the engine control unit (ECU). The ECU calculates the required fuel injection based on inputs such as engine speed, throttle position, and other engine parameters.
7. Advantages and Disadvantages: Throttle body fuel injection systems are generally less expensive and easier to maintain than MPFI systems. However, they may offer slightly lower performance and fuel efficiency due to their less precise fuel delivery and distribution.

Overall, throttle body fuel injection systems provide a simple and cost-effective means of delivering fuel to the engine, making them a common choice in many older vehicles. However, modern vehicles increasingly utilize more advanced multi-port fuel injection systems for improved performance and efficiency.