Federal Vehicles (Digifant II)

Digifant II Engine Management System:

The Digifant II control unit, which is located at the left rear of the engine compartment, is responsible for management of the fuel injection, ignition, and idle speed systems. 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
^ Knock sensor
^ Oxygen sensor
^ Throttle valve switches

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
^ Idle stabilizer valve
^ 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 meter 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, full throttle 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, oxygen sensor, or the knock 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.

Knock Sensor Location:

KNOCK CONTROL

The Digifant II control unit actively controls knock "ping" allowing calibration of the ignition timing for normal operating conditions, while eliminating the danger of knock or detonation due to influences by engine heat, load, fuel quality or engine deposits.

Knock Sensor Regulation:

When the Digifant II control unit recognizes a knock condition, the ignition point for that individual cylinder will be retarded 3.0°. If the knocking stops, the timing will be advanced in increments of .33° back to programmed values.
If knocking continues, the ignition point can be retarded up to 15° for an individual cylinder, however, it is limited to a maximum of 9° difference between cylinders.

Idle Stabilization Operation:

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 current to the idle stabilizer valve is changed. This change in current adjusts the valve opening to allow more or less air to bypass the throttle valve as necessary to maintain the correct idle speed.
The current from the control unit ranges from 380 mA to 1000 mA.
If a fault occurs in the coolant temperature sensor circuits, or when the sensor is disconnected for basic engine adjustments, the control unit will use a substitute value of approx. 420 mA to operate the idle stabilizer valve.