California Vehicles (Digifant I)

Digifant Engine Management System:

The Digifant I control unit, which is located under the dash on the right side by the glove box, is responsible for management of the fuel injection, ignition, and idle speed. It receives and evaluates information provided by various sensors concerning engine operating conditions. Input signals to the Digifant I control unit include:

^ A/C compressor "ON"
^ Air flow sensor
^ Coolant temperature sensor
^ Hall sender
^ Intake air temperature
^ Oxygen sensor
^ Throttle valve potentiometer

From the information received, the Digifant I control unit calculates appropriate values for the output components, which maintain optimum engine performance and emission characteristics. Output signals from the Digifant I control unit include:

^ Fuel Injectors
^ Fuel pump relay
^ Ignition Coil Power Stage

FUEL INJECTION CONTROL

Fuel injection quantity is controlled by the Digifant I control unit. The basic fuel injector opening time is calculated by the E.C.U. using information from the airflow sensor signal and the engine speed signal. The injector opening time (pulse width), is then modified by additional input signals to the E.C.U. for the functions of cold start enrichment, warm-up enrichment, deceleration fuel shut-off, and over-rev fuel shut-off; depending on engine operating conditions.

ADAPTIVE FUEL MIXTURE CONTROL

In order to maintain proper performance and driveability over a wider range of conditions, and to reduce the need for minor periodical adjustments, the Digifant I control unit can adapt to minor intake leaks, engine wear, and sustained high altitude operation. It does this by learning the control values that are most often required to maintain correct engine operation under normal conditions. If the "learned" conditions of operation change (i.e. changing from driving at sea level 35 ft., to mountain driving at 6000 ft.) the control unit will adapt the air/fuel mixture to prevent the rich or lean condition that would result otherwise.

NOTE: Because of the Digifant I control units adaptive capability, the Digifant control unit must be returned to its reference settings after testing, adjusting or replacing components.

FAULT MEMORY

In the event of a Digifant I system malfunction, fault information will be stored in the internal memory of the Digifant I control unit. Faults related to emissions and safety are stored in permanent memory and must be erased after repairs. Additional faults that can be recognized by the control unit are stored in a temporary fault memory and will be erased at the next engine start-up.
In addition to being stored in memory, an emissions-related failure will cause the "Check" light to illuminate on the instrument cluster.
Two methods may be used to retrieve fault codes. The VW special tool VAG 1551 tester, if availible, or using the special jumper cable # 357 971 514E which was placed in the car (trunk or glove box) by Volkswagen before being sold. These tools connect to the black, blue, and white connectors in the center console.

FAIL-SAFE OPERATION

In the event of a malfunction with either the coolant temperature sensor or oxygen sensor the Digifant I control unit will use a substitute value to continue engine operation until the malfunction can be repaired.

Timing Map:

IGNITION TIMING POINT

The ignition timing point is determined by the Digifant I control unit. Information on engine load, speed, and coolant temperature are processed by the control unit and compared to programmed "Basic Ignition Maps" in the control unit's permanent memory. These three dimensional ignition performance maps are used to optimize the ignition to achieve the most favorable exhaust gas and fuel consumption performance for any given load or speed condition.
When the throttle valve is in the closed position, the bottom line of the basic ignition map is selected as the idle/coast characteristic. For engine speeds below the nominal values, the ignition timing is advanced to obtain idle stabilization. For coasting, ignition timing is programmed to obtain minimum exhaust gas pollutants and optimum driveability performance. For the wide open throttle position, the top line of the basic ignition map is selected. For very high ambient temperatures, the ignition is retarded as a function of engine and intake air temperature.

IDLE STABILIZATION CONTROL

Idle speed is electronically controlled by the Digifant I control unit with relation to engine coolant temperature and engine load signals.
When the control unit recognizes that the idle speed is not within specified ranges, approx. 800-900 RPM, the necessary correction value is calculated and ignition timing is changed. This change in timing adjusts the engine rpm to maintain the correct idle speed.