Golf L4-1781cc 1.8L SOHC (1987)
Engine Control Module: Description and Operation
Digifant II System
Electronic Control Unit (E.C.U) (Digifant II)
DIGIFANT II
The E.C.U. is located in the engine compartment on the left side (driver's side) plenum
The heart of the Digifant II system is the new electronic control unit. The control unit incorporates all the functions of the fuel system and provides both
the actuation signal for the fuel injectors and optimum ignition timing point for all engine operating conditions.
The E.C.U. receives seven major input signals:
Engine speed:
- From the Hall sending unit.
Engine load:
- From the intake air volume.
Intake air temperature:
- From the air flow sensor temp. sensor.
Engine operating temperature:
- From the coolant temperature sensor.
Throttle position:
- From the throttle switches.
Oxygen content in the exhaust gas:
- From the oxygen sensor.
Spark knock threshold for the ignition timing:
- From the knock sensor.
Based on the information received from these seven major inputs, the Digifant E.C.U. generates the three major output signals necessary to control
engine operation under all conditions. The Digifant E.C.U. also controls the ground circuit for the fuel pump relay so the pumps run only when an RPM
signal is present.
Fail-safe functions are programmed into the control unit memory so the system will continue to operate in the event of a fault in the coolant temperature
sensor, oxygen sensor or knock sensor.
The Digifant E.C.U. generates the following three output signals:
Ground signal for the fuel injectors. This signal controls the amount of fuel injected into the engine by regulating the length of time the injectors
remain open. Cold start enrichment, warm-up enrichment, full throttle enrichment, fuel cut-off on deceleration, and fuel cut-off on over-rev (over 6500
RPM) are all controlled by regulating the ground for the fuel injectors.
Trigger signal for the ignition coil. This controls the exact moment the ignition coil fires each cylinder to ensure precise ignition timing under all
operating conditions. The Digifant E.C.U. monitors engine speed, engine load, coolant temperature, and intake air temperature, then selects the
