Fuel Injection System - Dual Unit TBI: Description

The General Motors dual unit (cross-fire) Electronic Fuel Injection (EFI) system consists of 9 major sub-assemblies: fuel supply system, Throttle Body Injector (TBI) assembly, Idle Air Control (IAC) system, Electronic Control Module (ECM), Electronic Spark Timing (EST), Electronic Spark Control (ESC), Hood Louver Control (HLC), data sensors and emission controls.

Fuel is supplied to engine through electronically pulsed (timed) injector valves located in separate throttle bodies on top of intake manifold (1 for each bank). Each throttle body unit is a Model 400 unit. The ECM controls amount of fuel metered through injector valves 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 system, ECM, HLC and data sensors. Because of the interrelated functions of the Computer Command Control (CCC) system (the ECM is the "brain"), see appropriate COMPUTER COMMAND CONTROL article in ENGINE PERFORMANCE section for more information.