Question

Explain the construction and working of throttle body injection (TBI) system. 

Answer 1

The throttle body injection (TBI) system uses one or two injector valves mounted in a throttle body assembly. The injectors spray fuel into the top of the throttle body air horn The TBI fuel spray mixes with the air flowing through the air horn. The mixture is then pulled into the engine by intake manifold vacuum. The throttle body injection assembly typically consists of the following: throttle body housing, fuel injectors, fuel pressure regulator, throttle positioner, throttle position sensor, and throttle plates. Throttle Body Injection is an electronically controlled injection system in which an electronic fuel injector injects the fuel intermittently in to the intake manifold at a central point ahead of the throttle valve. The central- injection unit operates at low pressure (0.7 to 1 bar) so; an inexpensive hydrodynamic electric fuel pump can be used (generally in the form an in-tank unit). The injector is flushed continuously by the fuel flowing through it in order to prevent the formation of air bubbles. The injector is a solenoid – controlled valve. The central injection unit uses the throttle valve to meter the intake air while injecting the fuel intermittently above the throttle valve. The intake manifold then distributes the fuel to the individual cylinders. Various sensors monitor all important engine-operating data, which are then used to calculate the triggering signals for the injectors and other system actuators.