Engine Controls - Tests W/Codes - DIGIFANT: Introduction

NOTE: Self diagnosis functions are only available on certain early production California models.

NOTE: Manufacturer has addressed significant technical concerns with the Digifant II system. Please refer to Volkswagen Technical Service Bulletins Group 90, No. 89-02 and Group 24, No. 89-07 .

In the Digifant II system, basic fuel metering is determined by engine RPM and by the volume and temperature of the air entering the engine. The Digifant II ECU receives air flow volume and temperature data from the air flow sensor and engine RPM data from the distributor, and distributes fuel to the engine through the fuel injectors.

Fuel injectors are triggered simultaneously at a rate that is proportional to engine RPM. Fuel mixutre is controlled by the length of the electrical impulse from the ECU.

Digifant II ECU makes additional adjustments to the amount of fuel delivered by the injectors based on input from various sensors. Oxygen sensor system provides the ECU with information on engine combustion effeciency by measuring the amount of oxygen in the exhaust stream. Switches on the throttle valve inform the ECU when the throttle is fully open or fully closed (at idle). A coolant temperature sensor on the cylinder head provides the ECU with engine temperature information for adjustments during starting and warmup.

In order for the system to operate properly, the basic adjustments to idle speed, ignition timing, idle mixture and throttle switches must be correct. If basic settings are incorrect, ECU will attempt to compensate and test results will be misleading.