Ignition System: Description and Operation
EZ69The electronic ignition system fitted, is a digital spark control, with hybrid control unit and a biased ignition coil made of plastics. Ignition is triggered by an inductive segment system, with a pulse generator sensing segments mounted on the flywheel.
IGNITION CONTROL UNIT
The control unit is based on a hybrid integrated circuit. Microprocessor, signal conditioning unit, pressure sensor and power stage are integrated into the control unit.
There are three electrical connectors and a manifold pressure sensing connection on the outside of the control unit and is mounted in the engine compartment.
NOTE: Control unit base plate must be coated with heat dispersion paste whenever removed and refitted, to improve heat dissipation.
IGNITION COIL
A permanent magnet used for magnetic biasing is built into the magnetic circuit of the ignition coil. Primary and secondary coils are mounted on plastic bobbins.
ENGINE SPEED SENSING
The six cylinder engine has three firing cycles per crankshaft revolution. The inductive pulse generator (speed/reference sensor) senses three segments located on the flywheel. The front edge of the segment generates a negative pulse and the rear edge a positive pulse. Those segment edges serve as reference marks correlated with a certain rotation angle of the crankshaft.
Pulse Generator:
The microprocessor measures period length to determine engine speed. The related ignition and dwell angles are then calculated, taking into consideration manifold vacuum (load), engine temperature and intake air temperature.
STARTING MODE
This mode is recognized by the microprocessor based on engine speed. The firing point is triggered at the positive edge of the pulse generator signal, approximately 15° BTDC. The control unit shifts from starting mode into operating mode (idle firing angle of 0° ±3° with 0° throttle switch closed) as soon as 630 rpm is exceeded. If engine speed drops below 330 rpm, the control unit will revert to starting mode.
OPERATING MODE
An idle/thrust curve (0° throttle switch) and an operating ignition map are stored in the ignition control unit. The optimum firing point for each operating condition is determined taking engine load, engine speed, engine temperature, intake air temperature, 0° throttle switch and fuel selector switch positions into account.
To adjust the firing point, the negative pulse generator edge of the control signal transmitted to the output stage is delayed by ascertain time interval calculated for the current speed. The delay tie calculated by the control unit is thus equivalent to the required spark advance. This is how the maximum firing point advance is determined.
INFORMATION SOURCES
Fuel Selector Switch
In certain countries, it may be inevitable to run the car on fuels with an octane rating below RON 95. In order to avoid random ignition taking place in the engine, the ignition may be retarded by 2.3° from a certain engine load via a 2-pin code plug using jumper 994.612.525.01.
Manifold Pressure Sensor
When starting the engine, the manifold pressure sensor is checked for short and open circuit. The firing angle of the full-load curve (1800 mbar) is output if pressure is below 750 mbar (short circuit) or above 1250 mbar (open circuit).
Since the pressure line from the intake manifold might be disconnected or kinked, even if the electrics of the pressure sensor are fully operational, a pressure of less than 770 mbar must be present at pressure sensor as soon as the 0° throttle switch has closed and after 2 seconds have elapsed. If this isn't the case, the firing angle corresponding to full load is again output.
Engine Temperature Sensor
An NTC temperature sensor used to register engine temperature, is located in the crankcase. This sensor is used to adjust ignition timing in accordance with temperature. The sensor is monitored for open circuit by the control unit. If an open circuit is detected, a replacement value is substituted.
Intake Air Temperature Sensor
A PTC temperature sensor is fitted to the intercooler. If intake temperatures are excessively high, the firing angle is retarded by the control unit by 2.8°, from a pressure of 1250 mbar at the pressure sensor.
Idle Switch
The 0° switch keeps the ignition control unit informed on idle and overrun modes of the engine.