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