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.

NOTE: Primary sub-systems which affect fuel system operation will be covered in this article: fuel supply system, TBI assembly, IAC assembly, ECM and data sensors. Because of the interrelated functions of the Computer Command Control (CCC) system (the ECM is the "brain"), refer to COMPUTER COMMAND CONTROL in COMPUTERIZED ENGINE CONTROLS section for more information.