SAAB WIS ONLINE

Ignition discharge module

Ignition discharge module


Ignition

The ignition discharge module is fitted on the camshaft cover. In the module there are 4 ignition coils, the secondary windings of which are connected directly to the spark plugs.

The ignition discharge module is supplied with B+ from the main relay and grounded to grounding point G7.

When the main relay operates, B+ is supplied to the ignition discharge module, which converts 12 V to 400 V DC and stores it in a capacitor. The 400 V current is connected to one of the terminals on the primary windings of the 4 ignition coils.

There are 4 trigger leads from the control module connected to the ignition discharge module as follows:


Cylinder 1 is connected to control module pin 7.

Cylinder 2 is connected to control module pin 54.

Cylinder 3 is connected to control module pin 55.

Cylinder 4 is connected to control module pin 8.


When the control module grounds pin 7, the other terminal on the primary winding on the ignition coil for cylinder 1 will be connected to the B+ input on the ignition discharge module. 400 V is then transformed up to maximum 40 kV in the ignition coil for cylinder 1. The ignition in cylinders 2, 3 and 4 takes place in the same way.

Diagnostics


If an open circuit occurs in the power supply to the ignition discharge module, the voltage on all the trigger leads will be 0 V and diagnostic trouble code P1310 will be generated.

No diagnostic trouble code will be generated if an open circuit occurs in an individual trigger lead.


System reaction to a fault


Fuel shut-off


Combustion signals, synchronization


The Trionic T7 has no camshaft position sensor as normally required for sequential knock control and fuel injection.

When starting, the control module does not know which of the cylinders 1 and 4 is in compression position and consequently ignition will take place simultaneously in both. Ignition takes place in cylinders 2 and 3 in the same way.

The control module must determine whether combustion is taking place in cylinder 1 or cylinder 4 and cylinder 2 or cylinder 3 respectively when they are triggered.

This is achieved 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.

Two detectors measure the voltage drop in pairs across cylinders 1+2 and cylinder 3+4 respectively. If combustion takes place in cylinder 1 or 2, the ignition discharge module will send a B+ pulse to control module pin 53. Similarly, the ignition discharge module will send a B+ pulse to control module pin 6 if combustion takes place in cylinder 3 or 4.

If cylinders 1 and 4 are triggered and a B+ pulse is received on control module pin 53 at the same time, the control module knows that cylinder 1 has fired.

As soon as combustion signals are received on control module pins 53 and 6, both ignition and fuel injection are synchronized to the engine firing order.

Combustion signals are also used to detect misfiring.


Diagnostics

Combustion signals

If an open circuit occurs on both leads to control module pins 53 and 6, there will be no synchronization of ignition or fuel injection. Knock detection is then performed in parallel on cylinders 1+4 and cylinders 2+3.


If an open circuit occurs in the lead to control module pin 53, diagnostic trouble code P1312 will be generated.

If an open circuit occurs in the lead to control module pin 6, diagnostic trouble code P1334 will be generated.

If the ignition cannot be synchronized with the camshaft position, diagnostic trouble code P0340 will be generated.


System reaction to a fault


Knock detection takes place in parallel on cylinders 1+4 and cylinders 2+3.


Note

Note

If a short to ground occurs in any of the two combustion signals, synchronization will take place and no diagnostic trouble code for the fault in question will be generated. A diagnostic trouble code for misfiring will be generated instead.


Misfiring


Emission-related misfiring will generate diagnostic trouble codes P0300-P0304 will be generated.

Misfiring that can damage the catalytic converter will generate P1300-P1304. CHECK ENGINE will flash while misfiring occurs.

If misfiring that can damage the catalytic converter occurs when the fuel level is below 4 litres, diagnostic trouble code P1390-P1394 will be generated. CHECK ENGINE will flash while misfiring occurs.


System reaction to a fault


Closed loop is blocked at high engine loads.