Ignition System: Description and Operation
Function of the breakerless transistorized ignition system (TSZ)
Only a 4-pin connector is plugged in at the small transistorized control module (distinguishing feature to ignition control module).
Components and function
transistorized control module (N1/1)
The transistorized control module is located or the left wheelhouse panel. It is designed in space-saving hybrid technology.
Pin assignment at transistorized control module
^ Green control lead from induction sensor in distributor (coaxial connector).
^ 4-pin round connector with terminals 15, 31, 16 and TO.
The electronic functions of primary current limitation and stall current cutoff in the transistorized control module enable the series resistors in the primary current circuit to be eliminated. Consequently, a higher ignition coil primary current and higher ignition capacity are possible.
The transistorized control module is activated by induction sensor in the distributor.
The optimal capacity of the ignition system is achieved by the dwell angle control in the transistorized control module. The dwell angle is controlled within the control range so that the same primary current is always achieved approximately in every operating state, i.e. at different battery voltages and engine speeds.
As a result of the elimination of the series resistors, the primary current is cut off by the transistorized control module (stall current cutoff) when the engine is not running and the ignition is switched on. The primary current is connected only once a certain pulse sequence is generated by the induction sensor in the distributor.
The maximum primary current of the ignition coil is determined by a current limiter in the transistorized control module.
The current limitation (C) can be recognized on the oscilloscope when the engine is at idle. Current limitation is no longer visible from an engine speed of approx. 2000/mm.
The power output stage switches the primary current of the ignition coil between terminals 16 and 31. In addition, the power output stage performs the task of limiting the primary current.
TD signal
The transistor engine speed (TD) signal is produced in the transistorized control module. This is an engine speed-dependent square-wave signal.
The engine speed is detected by the number of square-wave signals per minute.
When performing tests, the On time (t, e.g. 70% of the individual square-wave pulses is measured as dwell angle in degrees or as on/off ratio in percent (related to period, d).
The TD signal can be measured:
^ with the dwell angle tester or on/oft ratio tester in percent and degrees.
^ with the voltage meter 6 volts up to 12 volts direct voltage.
^ with the oscilloscope - square-wave signals.
Note: No TD signal exists if a short to ground is present at the connected equipment or at the diagnostic connector terminal block terminal TD (X11). To locate the problem, detach cable connection (arrow). Rectify short to ground in the respective circuit.
The following electronic components have a TO connection, e.g.:
Tachometer, CFI control module, fuel pump relay and compressor cutoff control module.
Ignition distributor (S5/2)
^ The induction sensor is installed in the distributor. It produces an alternating voltage up to approx. 100 volts for actuating the transistorized control module.
The alternating voltage passes along the green control cable (coaxial cable) to the ignition control module. The cable is a single-wire lead. The screening is used as a second lead.
^ Engine speed-dependent ignition advance by flyweights. Load-dependent ignition advance by vacuum (above approx. 60 °C coolant temperature).
^ Interference suppression resistors: distributor rotor 1 kohm (code number R1 on rotor), distributor cap 1 kohm per cylinder.
Ignition coil (T1)
The ignition coil is matched to the ignition control module and designed for a higher ignition capacity. Identification: yellow sticker.
The ignition coil must on no account be replaced by one of the previous ignition coils.
Distinguishing features from previous ignition coils are:
^ The safety plug in the cover of the ignition coil.
^ A higher dome.
^ Cable connection at terminal 1 with MS thread.
^ Cable connection at terminal 15 with M6 thread.
A 5.5 mm opening (arrow) which is sealed with a plug is located in the cover of the ignition coil. This cover detaches if an pressure as a result of severe heat formation is produced in the ignition coil by a defective output stage in the control module. The ignition coil is provided with a cover cap to prevent uncontrolled escape of the plug or of the sealing compound.
Ignition cables
The partially screened spark plug and angled distributor connectors are designed for high ignition voltage.
An interference suppression resistor of 1 kohm is installed in the spark plug connectors. These can be unscrewed (M3 thread).