General System Description

Fuel Injection Schematic:

The electronic, dual point fuel injection system uses a digital pre-programmed Single Module Engine Controller (SMEC) to control air-fuel mixtures delivered to the engine, ignition timing, idle speed, various emission control devices, the engine cooling fan and the charging system. The SMEC monitors inputs from various engine and vehicle sensors, computes ideal operating parameters for the controlled sub-systems based on these inputs, and controls operation of the subsystems. Sensors used to control system operations include: an exhaust gas oxygen sensor, Manifold Absolute Pressure (MAP) sensor, throttle position sensor, coolant and throttle body temperature sensors, vehicle distance sensor, and the neutral safety and A/C compressor clutch switches and auto shut down relay.
All inputs to the SMEC are converted to signals. These signals cause the SMEC to alter fuel injectors delivery and/or ignition timing to maintain ideal air fuel mixtures and ignition timing for all vehicle operating conditions.
In addition, the SMEC tests many of its input and output circuits, and if a fault is found in one of the monitored circuits information relating to the malfunction is stored in the SMEC memory. Information relating to monitored circuit malfunctions can be accessed by the technician through the instrument panel mounted check engine lamp, or by connecting a diagnostic read-out instrument to the system. Both access methods provide numerical type codes which relate to specific circuit malfunctions.
If the SMEC detects a fault in a signal sent from the MAP sensor, throttle position sensor or coolant temperature sensor, or if battery voltage drops or climbs abnormally, the system goes into ``limp-in'' mode. During limp-in mode, the SMEC replaces the failed signal with a modified signal, enabling the vehicle to remain drivable. Also during limp-in mode, the check engine lamp is illuminated.
The SMEC has been programmed to monitor several different circuits of the fuel injection system in order to provide a self-diagnosis function. In conjunction with the self-diagnosis function, a check engine lamp is wired into the system to indicate a failure in the monitored circuits. The check engine lamp is illuminated for 3 seconds whenever the engine is started as a `bulb test.' However, if the SMEC detects a malfunction in one of the monitored circuits the check engine lamp will be illuminated and will remain on as long as the ignition key remains in the on position. Illumination of the check engine lamp indicates that the system has entered the `limp-in' mode and signals an immediate need for system service.
If vehicle performance or the check engine lamp indicate fuel injection system malfunctions, certain procedures should be followed. Prior to suspecting the fuel injection service as the cause for complaints, ensure that the engine and all related systems are in proper operating condition. After checking related systems, inspect fuel injection components and connecting harnesses as outlined in `Visual Inspection,' repair system as indicated, then road test vehicle to check system operation. If service performed during visual inspection does not correct observed malfunctions, or if check engine lamp remains illuminated, refer to "On Board Diagnosis" to call up fault codes stored in the SMEC memory and correct as needed.