Throttle Body Injector Assembly
The throttle body injector (TBI) assembly is composed of 2 castings: a throttle body with a valve to control air flow and a fuel body with an integral pressure regulator and fuel injector. The throttle body casting may contain ports to generate vacuum signals for EGR valve, MAP sensor and canister purge system.
The pressure regulator is a diaphragm-operated relief valve with injector pressure acting on one side of the valve and air cleaner pressure acting on the other side of the valve. The pressure regulator maintains a constant pressure drop of about 10 psi (.7 kg/cm2 ) across the injector, throughout all engine operating conditions. See Fig 1 .
The fuel injector is a solenoid-operated device controlled by the ECM. Fuel is supplied at the lower end of the injector by the fuel supply system. The ECM activates the solenoid which lifts a normally closed ball valve off its seat. Fuel under pressure is injected in a conical spray pattern at the walls of the throttle bore, above the throttle valve. Excess fuel passes through the pressure regulator and is returned to the fuel tank.
During engine cranking, the fuel injector is pulsed (activated) once for each distributor reference pulse received by the ECM. This is referred to as the synchronized mode. In the non-synchronized mode, the injector is pulsed once every 6.25-12.5 milliseconds, depending upon engine calibration and operating conditions. In this mode, the pulse is totally independent of distributor reference pulses.