Schematic of the CDI Cassette on a SAAB 9-5 1998


Translation of the text:

Trionic T7 does not use a cam position sensor which is usually a must for sequential knock regulation and injection.

During startup the engine controler doesn't know which of the cylinders 1 and 4 is in the compressions stroke, as a result the controller fire both 1 and 4 at the same time. The same is true for ignition on cylinders 2 and 3.

The controller has to determine if the combustion occur in cylinder 1 or 4 and 2 or 3 respectively. This is done in the following way:

One of the primary coil connections is connected to the spark plug as usual but the other connection is not grounded as on a common ignition system but is connected to an 80v voltage. This means that there is an 80v potential over the spark gap except when the ignition occur.

When a combustion occur the temperature in the combustion chamber is very high, the fresh gas is ionized and start to conduct current. This means that a current flow over the spark gap without creating a spark. Because of the current flow over the spark gap the voltage over the spark gap will drop a lot. The voltage drop over the gap will be proportional to the pressure and temperature in the combustion chamber. The italics part is heavily simplified and wrong -Jörgen

430=Engine Controle Module (Trionic 7)

229=System Relay

Trionic does not have camshaft position sensor, it uses ion-sense in the CDI cassette to tell ECM which cylinder that is combusting.

In CDI cassette there are two "DET" components which means detonation sensing, one for cylinder 1+2 and one for cylinder 3+4, the "K" means signal upon knock and the "C" means signal upon combustion.

Upon start the ECM does not now which cylinder of number 1 and 4 that is in compression stroke and which that is in exhaust so ignition will happen on both, after that the ion-sense component

of the CDI cassette will sense which cylinder that actualy did a combustion and voilá - we have sync...

// Michael Pihlblad a.k.a. glidarn