Federal Vehicles (Digifant II)

Digifant II Engine Management System:

The Digifant II 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 II control unit include:

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

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

^ Fuel Injectors
^ Fuel pump relay
^ Hall control unit

FUEL INJECTION CONTROL

Fuel injection quantity is controlled by the Digifant II 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.

FAIL-SAFE OPERATION

In the event of a malfunction with either the coolant temperature sensor or oxygen sensor the Digifant II 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 II 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 II 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.