Ignition Management: Notes

Ignition Coils:  The high voltage supply required to ignite the mixture in the combustion chambers is determined by the stored energy in the ignition coils. The stored energy contributes to the ignition duration, ignition current and rate of high voltage increase. The Coil circuit including primary and secondary components consists of:

1. Coil Assembly 
   • Primary Winding 
   • Secondary Winding 
2. Insulator Boot 
3. Spark Plug 
4. ECM Final Stage Transistor 
5. Secondary Coil Ground 

The Coil Assembly contains two copper windings insulated from each other. One winding is the primary winding, formed by a few turns of thick wire. The secondary winding is formed by a great many turns of thin wire.

The primary winding receives battery voltage from the ECM Relay (Coil Terminal 15). The ECM provides a ground path for the primary coil (Coil Terminal 1) by activating a Final Stage transistor. The length of time that current flows through the primary winding is the "dwell" which allows the coil to "saturate" or build up a magnetic field. After this storage process, the ECM will interrupt the primary circuit at the point of ignition by deactivating the Final Stage transistor. The magnetic field built up within the primary winding collapses and induces the ignition voltage in the secondary winding.

The high voltage generated in the secondary winding is discharged through Coil Terminal 4 to the spark plug (insulated by the boot connector).

The primary and secondary windings are uncoupled, therefore, the secondary winding requires a ground supply (Coil Terminal 4a).

There is an individual ignition circuit and coil for each cylinder on the MS S54 system. The S54 uses "pencil type" ignition coils manufactured by Bremi. The six individual ignition coils are integrated with the insulated connector (boot).

The coils are removed by lifting the swivel latch connector retainer to release the wiring harness, apply a slight twist and lift the assembly upwards.

The primary ignition cables are routed on the top of the cylinder head cover. A suppression capacitor is installed on the secondary ignition ground circuit (arrow).

Spark Plugs:  The spark plugs introduce the ignition energy into the combustion chamber. The high voltage "arcs" across the air gap in the spark plug from the positive electrode to the negative electrodes. This creates a spark which ignites the combustible air/fuel mixture.

The spark plugs are located in the center of the combustion area (on the top of the cylinder head) which is the most suitable point for igniting the compressed air/fuel mixture.

The correct spark plugs for the S54 are NGK DCPR8EKP dual electrode (non-adjustable gap).

Faults with the Ignition Output Components  are monitored by the ECM. If there are faults with the ignition coil(s) output, and/or spark plugs, the following complaints could be encountered:

1. "ENGINE EMISSION" Light with Mixture Related and/or Misfire Fault Codes 
2. Poor Engine Performance 
3. Engine Misfire 
4. No Start/Hard Starting 
5. Excessive Exhaust Emission/Black Smoke 

The Ignition Output Components must be individually tested (see WORKSHOP HINTS  ).

The primary ignition  circuits are monitored by the ECM.

If a fault is present, the "ENGINE EMISSION" Light will illuminate and the ECM will deactivate the corresponding fuel injector for that cylinder. Engine operation will still be possible.

The secondary ignition  is monitored by the ECM via the Crankshaft Position/RPM Sensor.

If a Misfire fault is present, the "ENGINE EMISSION" Light will illuminate and the ECM will deactivate the corresponding fuel injector for that cylinder. Engine operation will still be possible.

Knock Sensors:  are required to prevent detonation (pinging) from damaging the engine. The Knock Sensor is a piezoelectric conductor-sound microphone. The ECM will retard the ignition timing (cylinder selective) based on the input of these sensors. Detonation can occur due to:

1. High Compression Ratio 
2. Poor Quality Fuel (Octane Rating) 
3. High Level of Cylinder Filling 
4. Maximum Timing Advance Curve 
5. High Intake Air and Engine Temperatures 
6. Carbon Build-Up (Combustion Chamber) 

The Knock Sensor consists of:

1. Shielded Wire 
2. Cup Spring 
3. Seismic Mass 
4. Housing 
5. Inner Sleeve 
6. Piezo-Ceramic Element 

A piezo-ceramic ring is clamped between a seismic mass and the sensor body. When the seismic mass senses vibration (flexing), it exerts a force on the piezo-ceramic element. Opposed electrical charges build up on the upper and lower ceramic surfaces which generates a voltage signal. The acoustic vibrations are converted into electrical signals. These low voltage signals are transmitted to the ECM for processing.

There are three Knock Sensors bolted to the engine block between cylinders 1 & 2, 3 & 4 and 5 &6. If the signal value exceeds the threshold, the ECM identifies the "knock" and retards the ignition timing for that cylinder.

If a fault is detected with the sensor(s), the ECM deactivates Knock Control and the "ENGINE EMISSION" Light will be illuminated. The ignition timing will be set to a conservative basic setting based on intake air temperature and a fault will be stored.

Crankshaft Position/RPM Sensor:  This sensor provides the crankshaft position and engine speed (RPM) signal to the ECM for ignition activation and correct timing. This input is also monitored for Misfire Detection. For details about the sensor, refer to the FUEL MANAGEMENT  section.

A fault with this input will produce the following complaints:

1. No Start 
2. Intermittent Misfire/Driveability 
3. Engine Stalling 

Camshaft Position Sensor (Cylinder Identification):  The camshaft sensors (Hall type) inputs allows the ECM to determine camshaft positions in relation to crankshaft position. It is used by the ECM to establish the "working cycle" of the engine for precise ignition timing. For details about the sensor, refer to the FUEL MANAGEMENT  section.

If the ECM detects a fault with the Camshaft Sensors, the "ENGINE EMISSION" Light will be illuminated and the ignition will still operate based on the Crankshaft Position/RPM Sensor.

Engine Coolant Temperature:  The ECM determines the correct ignition timing required for the engine temperature. For details about the sensor, refer to the FUEL MANAGEMENT  section. This sensor is located in the coolant return pipe on the cylinder head (1).

If the Coolant Temperature Sensor input is faulty, the "ENGINE EMISSION" Light will be illuminated and the ECM will use the oil temperature sensor as an alternate. The ignition timing will be set to a conservative basic setting.

Accelerator Pedal Position (PWG):  As the accelerator pedal is actuated, the ECM will advance the ignition timing. The "full throttle" position indicates maximum acceleration to the ECM, the ignition will be advanced for maximum torque.

For details about the sensor, refer to the AIR MANAGEMENT  section.

Hot-Film Air Mass Meter (HFM):  The air volume input signal is used by the ECM to determine the amount of ignition timing advance.

For details about the sensor, refer to the AIR MANAGEMENT  section.

Air Temperature:  This signal allows the ECM to make a calculation of air density. The sensor is located in the HFM. For details about the sensor, refer to the AIR MANAGEMENT  section.

The ECM will adjust the ignition timing based on air temperature. If the intake air is hot the ECM retards the ignition timing to reduce the risk of detonation. If the intake air is cooler, the ignition timing will be advanced.

If this input is defective, a fault code will be set and the "ENGINE EMISSION" Light will illuminate. The ignition timing will be set to a conservative basic setting.