How many injectors does a throttle body have?
In practice, the number of injectors in a throttle body depends on the fuel-delivery design. A throttle body can contain two injectors in throttle body injection (TBI), or one injector in single-point throttle body injection (SPI). In most modern engines, however, injectors are located at each cylinder’s intake port, not inside the throttle body at all.
Understanding this difference matters for maintenance, repair, and troubleshooting. The throttle body is primarily an air-control device, while the fuel injectors may be housed in the throttle body (in older TBI/SPI designs) or located at the ports (in port fuel injection). This article outlines the main configurations and what to expect from them on real-world engines.
Common throttle body injector configurations
Throttle Body Injection (TBI) with two injectors
Two injectors are mounted inside the throttle body and spray fuel into the plenum behind the throttle plate. The engine computer coordinates both injectors to deliver the proper fuel mist as air flows into the intake runners.
- Two high-pressure injectors placed side-by-side within the throttle body.
- Injectors spray into the plenum to supply all cylinders through the intake runners.
- Historically prevalent on many 1980s–1990s V6 and V8 engines from American automakers and some imports.
This two-injector arrangement was a bridge between early single-point systems and the widespread adoption of port injection, offering a simpler design while providing adequate fuel distribution for many engines of the era.
Single-Point Injection (SPI) in the throttle body
In SPI designs, a single injector sits in the throttle body and feeds fuel into the plenum, with the mixture distributed to the cylinders as air moves through the intake.
- One injector located in the throttle body.
- All cylinders rely on a single fuel spray pattern via the plenum and runners.
- Seen on some smaller engines or older EFI setups; less common on newer mainstream models.
SPI TB setups are simpler and cheaper, but distribution can be less uniform across all cylinders compared with multi-point approaches, especially on higher-output or multi-bank configurations.
Modern port fuel injection (PFI) and no injectors in the throttle body
The dominant current configuration places injectors at each cylinder’s intake port, outside the throttle body, while the throttle body handles air flow control and sensors.
- Injectors located at the intake ports for precise fuel delivery per cylinder.
- The throttle body typically contains only the throttle plate, an idle air control valve, and related sensors.
- This arrangement offers improved fuel metering, emissions performance, and efficiency on most contemporary engines.
While rare exceptions exist (some specialized or legacy designs), the port-injector arrangement is the standard in modern gasoline engines and means the throttle body itself does not contain injectors.
Summary
The number of injectors in a throttle body varies by design: two injectors for typical throttle body injection, one for single-point throttle body injection, and none for most modern port fuel-injected engines. Knowing which configuration your vehicle uses helps with diagnostics, maintenance, and repairs.
