Direct Ignition System
Ignition module
This module is the central component of a distributorless system. It contains two dual ignition coils and driver electronics which amplify the ignition signals from the Multec control unit. Each coil has two high voltage outputs, thus supplying two spark plugs.
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The control unit starts ignition via two signal outputs. Each lead (EST A and EST B) actuates one coil. Coil 1 ignites cylinders 1 and 4, coil 2 cylinders 2 and 3. When the control unit sends the ignition signal EST A (terminal C-1/4 is pulsed to ground), coil 1 induces a high voltage pulse. Each coil simultaneously ignites one cylinder with combustible and one with combusted mixture.
Electronic ignition signals (EST)
The EST input receives a voltage signal from the control unit
EST signal
The two dual ignition coils are supplied with the necessary ignition energy by the dual ignition coil driver module. This primary current builds up a magnetic field in the primary winding.
When the control unit has determined the point at which ignition must occur using the ignition map, the primary current (EST signal) is switched off (dwell angle algorithm). The magnetic field, which has flowed through the primary and the secondary winding, collapses. The resulting high voltage is led via the two high voltage cables of the dual ignition coil and the spark plug electrodes to the engine ground.
The two ignition signal phases are displaced by 180°.
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Up to MY '92, the EST switch level was 0 V and 12 V. This is altered as of MY '93. The Transistor-Transistor-Logic (TTL) now supplies the typical voltage values of 0 V and 5 V.
The dwell angle algorithm of the control unit has two different modi:
Starting mode and operating mode
In the starting mode, the dwell period (EST on) is dependent on a fixed angle in °CA and battery voltage. In the operating mode, the dwell period is based on the relationship between engine speed and battery voltage as stored in the dwell angle map.
The transition from the starting mode to the operating mode occurs at approx. 400 rpm.
Dwell period in starting mode
| Battery voltage | Magnetic field starts to build up at |
|---|---|
| greater than 12 V | 18° to 24° CA before ignition point |
| less than 10 V | 36° to 42° CA before ignition point |
Voltage limitation
The operating range of the DIS lies between 6 V and 16 V. However, overvoltage of up to 24 V or reversal of the supply voltage and ground leads will not lead to damage, as long as it does not persist for longer than 60 s.
Diagnosis
As of MY '93, the engine control unit is able to recognize short circuits to ground and short circuit to battery voltage in the EST leads in the entire engine speed range. As soon as a fault is recognized, the engine control unit activates the telltale.
As of MY '93, an ignition Actuator Test is possible for the EST B and A leads.
Terminal Assignment
B+ Switched battery voltage, Ter. 15
Masse Connection to vehicle ground
EST 1/4 und 3/2 Input signal from control unit (0 volts or 5 volts)
Installation
The DIS module is installed as a complete unit.
The three fastening bolts (arrows) of the DIS module are tightened to a torque of 7 Nm/5 lbf. ft.
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Ignition coil characteristic data
| Secondary resistance | 6 kW ± 0.05 kW |
|---|---|
| Engine speed range | 30 to 8000 rpm |