is lost, the charging pressure is lowered to basic charging pressure and the ignition timing advance is lowered 12° when it exist a risk of knocking due to engine load. Combustion signals The Trionic system lacks a camshaft position sensor. This sensor is normally a prerequisite for a sequential pre ignition/pinging regulation and fuel injection. Saab Trionic must decide whether cylinder one or cylinder four ignites when the crank shaft position sensor indicates that cylinder one and four is at TDC. This is done by help of ionization current. One of the poles of the secondary coil of the spark coils is connected to the spark plugs in an ordinary manner. The other pole isn’t grounded directly but connected to an 80 V voltage. This means that an 80 V voltage is applied across the spark gap of the spark plugs, except when the spark is fired. When combustion has occurred the temperature in the combustion chamber is very high. The gases are formed as ions and start to conduct electric current. This results in a current flowing in the spark plug gap (without resulting in a spark). The ionisation current is measured in pairs, cylinder one and two is one pair and cylinder three and four in the other pair. If combustion occurs in cylinder one or two the ignition cassette sends battery voltage (B+) pulse to the ECU, pin 17. If the combustion takes place in cylinder three or four the B+ pulse is fed to pin 18 in ECU. If the crankshaft position sensor indicates that cylinders one and four are at TDC and a B+ pulse enters the ECU via pin 17 simultaneously, then the ECU know that it is cylinder one that has ignited. Upon starting, the ECU doesn’t know which cylinder is in compression phase, hence ignition is initiated in both cylinders one and four and 180 crank shaft degrees later sparks in cylinder two and three are fired. As soon as the combustion signals enters the ECU via pin 17 and pin 18 the ignition and fuel injection is synchronised to the engines firing order. The combustion signals are also used to detect misfires. Heat plates Heat plates are used to lower the warm up emissions. They vaporize the injected fuel before it is drawn/forced into the cylinders and consequently reduce the need for added fuel in the A/F mixture in the warm