Throttle Body Injector Assembly
TBI assembly consists of 2 castings, throttle body and fuel meter assembly. Throttle body has throttle valve, Idle Air Control (IAC), and Throttle Position Sensor (TPS). The fuel meter body has fuel meter assembly, pressure regulator and 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 pressure above 9 psi (.6kg/cm2 ) to prevent poor engine performance. See Fig 1 .
Fuel injector is a 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 a 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.