V 2500 P/U 4WD V8-350 5.7L (1987)
Throttle Body: Description and Operation
IAC Valve Operation And Fuel Pressure Regulation
The Throttle Body Injector (TBI) unit is made up of two major castings: a throttle body and a fuel body. The throttle body contains an Idle Air Control
(IAC) valve to control idle air flow and a throttle position sensor mounted on the throttle valve shaft. The fuel body contains a fuel meter cover with an
integral fuel pressure regulator to maintain constant fuel pressure and an injector on 4 cylinder models or injectors on V6 and V8 models.
The throttle body portion of the TBI may also contain several ports located above or below the throttle valve(s) to provide vacuum signals to various
vacuum operated equipment.
Each fuel injector is a solenoid operated device controlled by the ECM. Incoming fuel is directed towards the lower end of the injector assembly, Fig. 2.
When the ECM actuates the injector solenoid, the normally closed ball valve is lifted off its seat and pressurized fuel is injected in a conical spray pattern
at the TBI bore wall(s) above the throttle valve(s). Excess fuel is routed through the pressure regulator before being returned to the fuel tank.
The fuel pressure regulator is integral with the TBI fuel meter cover and is serviced as an assembly with the meter cover only.
