Volkswagen Golf/Jetta/Cabriole 1990-1999

Digifant Fuel Injection System



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Fig. View of a typical Digifant fuel system

The Digifant system is all electronic, using electric injectors at a relatively low injection pressure. All injectors are operated by the Electronic Control Unit (ECU) so injector opening timing and duration can be closely controlled for reduced emissions and improved fuel mileage. During deceleration above about 1500 rpm, the injectors are shut off to save fuel and reduce emissions. The system uses an air vane and potentiometer type air flow sensor and an inlet air temperature sensor to calculate air flow into the engine. An idle stabilizer valve is used to control idle speed. This is a motorized rotary valve that controls the amount of air allowed to bypass the throttle plate.

The fuel pump is mounted in a reservoir under the vehicle along with the filter. The reservoir holds about 1 liter of fuel and is supplied by a small transfer pump in the fuel tank. The transfer pump is part of the fuel gauge sending unit assembly but it can be replaced separately.

The electric fuel injectors are secured in place by the fuel rail, which also houses the wiring. All injectors are wired together in parallel and are operated at the same time. Power is supplied to all injectors any time the ECU is receiving an rpm signal.

Other components in the Digifant system include the oxygen sensor, a coolant temperature sensor, a throttle position switch, the idle air stabilizer valve, the fuel system pressure regulator and the ignition system. The function and testing of fuel system items is described in , Electronic Engine Controls.

Most of the following procedures will produce fuel vapors. Make sure there is proper ventilation and take the appropriate fire safety precautions.