9-5 Wagon (9600) L4-2.3L Turbo (B235) (1999)
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Combustion Signals, Synchronization
The Trionic T7 has no camshaft position sensor as normally required for sequential knock control and fuel injection.
On starting, the control module does not know which of cylinders No. 1 and No. 4 is in the compression position, so ignition takes place in both these
cylinders at the same time. Ignition takes place in cylinders No. 2 and No. 3 in the same way.
The control module must determine whether ignition takes place in cylinder No. 1 or cylinder No. 4, and also in cylinder No. 2 or No. 3 when these are
triggered. This is done as follows.
One pole of the secondary windings of the 4 ignition coils is normally connected to the relevant spark plug. The other pole is not grounded direct but
connected to 80 V. This means that a voltage of 80 V is always present across the spark plug gap except just as the spark is produced.
When combustion takes place, the temperature in the combustion chamber is very high. The gases are ionized and begin to conduct current. This means
that current passes between the spark plug electrodes without producing a spark.
As the circuit is completed between the spark plug electrodes, the current (80 V) flowing across the gap drops sharply. The voltage drop will be
proportional to the pressure and temperature in the combustion chamber.
