VW T4 minibuses are equipped with an electronic ignition system that has a single microprocessor module with a Digifant .
The ignition system ensures the generation and supply of an electric spark to the cylinders of a gasoline engine at the optimal time to ignite the air-fuel mixture.
In the ignition system, the battery voltage (12V) is converted to a voltage of 25,000 - 30,000 V at the spark plug. The electronic ignition system is not subject to wear and requires almost no adjustment and maintenance.
The presence of semiconductor parts makes the ignition system reliable, but, unfortunately, reduces the possibility of repairs to a minimum. The ignition system includes the following main components:
- ignition lock
- spark plugs
- high voltage converter (ignition coil, switch, power amplifier)
- ignition distributor with Hall sensor
- microprocessor control module of the Digifant system
The ignition distributor is equipped with a Hall sensor instead of interrupter contacts.
The ignition timing is set by the electronic module and corrected by a vacuum corrector, which is connected by a hose to the intake manifold.
The corrector located in the module converts the pressure value into an electrical impulse. The magnitude of this pulse depends on the load on the engine, and the crankshaft speed is determined by the duration of the intervals between pulses. The electronic module selects the appropriate range of ignition timing, depending on the current speed and engine load. Thus, the amount of ignition advance changes regularly and corresponds to the current operating conditions of the engine. The ignition distributor is located in the side wall of the cylinder block and is driven by the oil pump shaft.
The battery voltage is applied to the pulse sensor (Hall sensor) in the ignition distributor, and then converted into high voltage in the ignition coil is applied to the spark plugs.
The central high-voltage wire of the ignition coil is connected to the central contact of the ignition distributor.
The current passes through the distributor runner in turn to the four contacts of the distributor cap, and from there to the corresponding spark plugs. The ignition timing is changed electronically by a microprocessor module. The injection and ignition systems have a common electronic microprocessor control module, which is equipped with a fault code memory. It accumulates fault codes that occur in the engine electronics when traveling. Before repairing the ignition system, it is necessary to check the accumulated readings of the fault memory block. The check is performed using a special device VW 1551 through the black and white diagnostic connectors located in the relay box.