Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Throttle Body Injector Assembly
TBI assembly consists of 2 castings, throttle body and fuel meter assembly. Throttle body has throttle valve, Idle Air Control (AC), and Throttle Position Sensor (TPS). The fuel meter body has fuel meter assembly, pressure regulator and injector. Throttle body casting may contain ports to supply vacuum signals for EGR valve, MAP sensor and canister purge system.
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 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.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.