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.
Fuel Injection System - Single Unit TBI: Description
The General Motors single unit Electronic Fuel Injection (EFI) system consists of 7 major sub-assemblies: fuel supply system, Throttle Body Injector (TBI) assembly, Idle Air Control (IAC) system, Electronic Control Module (ECM), Electronic Spark Timing (EST), data sensors and emission controls.
The Model 300 TBI assembly is used on 1.8L and 2.5L engines. The Model 500 TBI unit is used only on the 2.0L engine. The major difference between the 2 models is that the Model 500 has the Throttle Position Sensor (TPS) and throttle lever located on opposite sides from the Model 300.
Fuel is supplied to engine through an electronically pulsed (timed) injector valve located in throttle body unit on top of intake manifold. The ECM controls amount of fuel metered through injector valve based upon engine demand and efficiency information. The ECM is a digital electronic computer which receives and computes signals from various data sensors.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- β’ You smell fuel, burning insulation, or see smoke.
- β’ Brakes feel soft, pull hard to one side, or make grinding noises.
- β’ The engine overheats, stalls repeatedly, or misfires under load.
- β’ You are missing required tools, torque specs, or safe lifting equipment.
- β’ You are not confident in the next step or safety outcome.