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 optimum ignition timing point from an internal timing "map." The knock sensor allows the Digifant E.C.U. to maintain ignition timing as advanced as possible for good performance while eliminating the possibility of detonation or spark knock.
Control current for the idle stabilizer. This regulates the opening and closing of the idle stabilizer valve to control the amount of idle air that bypasses the throttle plate. If the idle speed varies from the value stored in the E.C.U., it compensates by opening or closing the stabilizer valve.
The E.C.U. also receives a signal when the A/C compressor clutch is activated. The E.C.U. increases control current by a predetermined amount when the A/C clutch is activated. This prevents a severe idle speed dip before the idle stabilization system can compensate. The current increase remains effective for as long as the compressor clutch is engaged.
The control current output also increases idle speed during warm-up enrichment and for a short period following a hot start at high outside temperatures.
Relay Location
Power Supply Relay
Provides battery voltage to the E.C.U. in the Colt. Provides battery voltage to the E.C.U. AND the fuel injectors In the Jetta.
Fuel Pump Relay
Provides battery voltage to the fuel pumps and fuel injectors In the Golf. Provides battery voltage to the fuel pumps and oxygen sensor heating element In the Jetta.
Note: These relay locations are valid for vehicles produced before January 1989.