GM Metro/Sprint 1985-1993 Repair Guide

Electronic Fuel Injection (EFI) Turbo System


See Figures 1 and 2

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Fig. Fig. 1: EFI Turbo system schematic

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Fig. Fig. 2: EFI Turbo system wiring diagram


The EFI Turbo system is used only on 1987-88 turbocharged Sprint vehicles. The system, namely the electronic control type fuel injection system, consists of an ECM, an in-tank type electric fuel pump, a pressure regulator, fuel injectors, a turbocharger, a throttle position sensor, an intake air temperature sensor, a coolant temperature sensor, an oxygen sensor, an airflow meter and others.

Electronic Control Module (ECM)

The ECM is required to maintain the exhaust emissions at acceptable levels. The module is a small, solid state computer which receives signals from many sources and sensors; it uses these data to make judgments about operating conditions and then control output signals to the fuel and emission systems to match the current requirements.

Inputs are received from many sources to form a complete picture of engine operating conditions. Some inputs are simply Yes or No messages, such as that from the Park/Neutral switch; the vehicle is either in gear or in Park/Neutral; there are no other choices. Other data is sent in quantitative input, such as engine RPM or coolant temperature. The ECM is pre-programmed to recognize acceptable ranges or combinations of signals and control the outputs to control emissions while providing good driveability and economy. The ECM also monitors some output circuits, making sure that the components function as commanded. For proper engine operation, it is essential that all input and output components function properly and communicate properly with the ECM.

Since the control module is programmed to recognize the presence and value of electrical inputs, it will also note the lack of a signal or a radical change in values. It will, for example, react to the loss of signal from the vehicle speed sensor or note that engine coolant temperature has risen beyond acceptable (programmed) limits. Once a fault is recognized, a numeric code is assigned and held in memory. The CHECK ENGINE dashboard warning lamp will illuminate to advise the operator that the system has detected a fault.

In the event of an ECM failure, the system will default to a pre-programmed set of values. These are compromise values which allow the engine to operate, although possibly at reduced efficiency. This is variously known as the default, limp-in or back-up mode. Driveability is almost always affected when the ECM enters this mode.

Check Engine Lamp

The primary function of the dash warning lamp is to advise the operator that a fault has been detected, and, in most cases, a code stored. Under normal conditions, the CHECK ENGINE lamp will illuminate when the ignition is turned ON . Once the engine is started and running, the ECM will perform a system check and extinguish the warning lamp if no fault is found.

Additionally, the dash warning lamp must be used to retrieve stored codes after the system is placed in the Diagnostic Mode. Codes are transmitted as a series of flashes with short or long pauses.


If a fault occurs intermittently, such as a loose connector pin breaking contact as the vehicle hits a bump, the ECM will note the fault as it occurs and energize the das