General System Description

Fig. 1 Digifant II System Layout:

The Digifant II system, Fig. 1, is an electronic multi-point fuel injection system. This system uses various sensors to convert engine operating conditions into electronic signals. These signals are processed by the control unit, which regulates the air/fuel mixture by varying the duration of injector opening.
The Digifant II system provides central microprocessor control of ignition system operation and fuel injection. The system uses an Electronic Control Unit (ECU) which monitors engine and vehicle operating conditions through a variety of sensors to determine proper ignition timing and the amount of fuel required for proper engine operation. The ECU monitors crankshaft position, engine speed and temperature, intake air flow volume and temperature, throttle position, vehicle speed, and exhaust gas oxygen content in order to compute proper ignition timing and the amount of fuel required to maintain acceptable engine performance while controlling exhaust emissions.
The ECU controls ignition timing by controlling current switching in the primary circuit, based on signals from the distributor, coolant temperature and air temperature sensors.
Electronic fuel injection is controlled by the ECU based upon signals from sensors which monitor engine and vehicle operating conditions and signals from the exhaust gas oxygen sensor. The ECU controls operation of the fuel pump, cold start system and idle speed control, and provides the ground circuit to control fuel injector operation.

Fig. 3 On Board Diagnostic System Indicator Switch:

For California vehicles only, an On-board Diagnostic System provides fault recognition for both the ignition and fuel injection systems. The Digifant II system control unit has an erasable permanent memory which stores and displays faults that could cause the vehicle to fail an exhaust emission inspection. Fault codes are displayed by an indicator rocker switch on the instrument panel marked CHECK, Fig. 3.
When the ignition is turned on, the CHECK light must come on briefly. After activating the fault memory, the CHECK light must flash. Refer to procedure outlined under " Activating Fault Memory". The control unit stores faults that affect the ability of the vehicle to pass an exhaust emission inspection. These faults can only be detected and stored after the vehicle is driven for a minimum of ten minutes. If a fault is detected and stored in the control unit, the CHECK light will come on after one minute.

Fig. 4 Fault Code:

A fault code consists of a series of four flash impulse groups with a maximum of four flash impulses per group. Between each impulse group there is a 2.5 second pause (CHECK light off). To determine a fault code, count the number of flashes within each group, Fig. 4. In this example, code 2342 (oxygen sensor) is shown.