Ignition Discharge Module (IDM) is mounted on the camshaft cover over the spark plugs. It has a 10-pin connector.
The main relay supplies 12 volts of power to IDM, which converts it to 400 volts DC and charges a capacitor with the voltage. The 400 volts are supplied to one pole of the four ignition coils- primary windings.
Four trigger wires from ECM connect to IDM via four pins: 9 through 12, which trigger cylinders 1 through 4, respectively. When ECM grounds a pin, the other pole of the ignition coil-s primary winding will be grounded via IDM power input. The 400 volts transforms to 40,000 volts, igniting the cylinder.
To facilitate engine starting when coolant temperature is below 32°F (0 °C), ECM will ground each trigger wire 210 times per second from 10° BTDC to 20° ATDC. This multi-spark function ceases when engine speed reaches idle.
At idle, a programmed ignition control curve advances timing under normal conditions up to 8°, and up to 20° when under sudden, auxiliary electrical load. When engine speed increases above idle, normal ignition control parameters resume.
Because the SAAB Trionic system does not use camshaft position sensor, it uses the crankshaft position (CKP) sensor to determine which cylinders are firing. The ignition coil pole that is not connected to the spark plug is connected to 80 volts, not ground. 80 volts is always present across the spark plug except when a spark is produced. When cylinder combustion occurs, gases ionize and conduct current across the spark plug gap without creating a spark. The ionization current is measured in cylinder pairs 1 and 2, or 3 and 4. The IDM sends a power pulse to ECM pin 17 if it measures ionization current from cylinders 1 or 2, and to ECM pin 18 if it measures ionization current from cylinders 3 or 4. If CKP indicates cylinders 1 and 4 are at TDC, and ECM pin 17 receives a power pulse from IDM, the ECM knows cylinder 1 has fired. The same process occurs for each cylinder.
For knock control, the SAAB Trionic system does not use a standard knock sensor. Instead, IDM analyzes cylinder combustion ionization currents and sends signals to ECM pin 44. If ECM detects sufficient knocking at any cylinder, it instructs IDM to retard ignition timing 1.5° at the knocking cylinder. If cylinder knocking continues, IDM retards ignition timing incrementally, up to 12° maximum, until knocking stops.
If cylinder knocking occurs when intake manifold pressure exceeds about 20 psi (140kPa), knock control measures change. Initially, ECM will adjust fuel injection and ignition parameters. If those adjustments are insufficient, ECM will reduce turbocharger boost pressure.
The main relay remains active for 6 seconds after ignition has been switched OFF. ECM then grounds all trigger wires to IDM at 210 times per second for 5 seconds, creating 1,050 sparks per cylinder, which allow spark plugs to burn off combustion residues.
Removal & Installation
Disconnect IDM electrical connector. Remove 4 attachment screws or bolts. Lift up IDM.
Reverse removal procedure. Tighten attachment screws or bolts to 8 ft. lbs. (11 Nm). Spray electrical connector with Kontakt 61 or other anti-corrosive lubricant. Spray rubber seals with synthetic lubricant.
To change IDM spring:
- Remove 8 screws from underneath IDM and remove black, lower section of IDM.
- Use screwdriver to pry out spring.
- Replace old spring with a new one.
Install black, lower section of IDM and install 8 screws.
No knock signal from IDM can be caused by an open circuit to ECM pin 44. DTC P0327 will be set.
Engine will not start if there is a break in IDM power supply or grounding.
A misfire DTC will set if there is a break in ignition wiring.
If ignition and fuel injection synchronization does not occur, knock control measures will be performed in parallel on cylinders 1 and 4, and cylinders 2 and 3.
If there are open circuits in wiring to ECM pin 17 and 18, ignition and fuel injection will not be synchronized and DTC P0340 will be set.
If a short circuit to ground occurs at wiring to ECM pins 17 and 18, ignition and fuel injection will be synchronized, but DTC P0300 will be set to indicate misfiring in more than one cylinder.
Misfiring in one cylinder will set DTC P0301 to P0304, depending on which cylinder is misfiring.