Ignition System: Description and Operation

Ignition Control

Ignition Control is determined by the EMS2000 (load dependent). the EMS2000 will calculate the engine "load" based on a combination of the following inputs:

- Battery Voltage.
- Accelerator Pedal Position.
- Calculated air volume and mass.
- Engine Coolant Temperature.
- Crankshaft and Camshaft Position.
- Knock sensors.

the dwell time will be regulated based on battery voltage. When cranking, the voltage is low and the EMS2000 will increase the dwell to compensate for saturation "lag time". When the engine is running and the battery voltage is higher, the EMS2000 will decrease the dwell due to faster saturation time.

the Crankshaft Position/RPM signals the EMS2000 to start ignition in firing order (1-3-4-2) as well as providing information about the engine operation. This input is used in combination with other inputs to determine engine load which advances/retards the ignition timing. Without this input, the EMS2000 will not activate the ignition.

Cold start is determined by the EMS2000 based on the engine coolant temperature and rpm during start up. A cold engine will crank over slower than a warm engine, the ignition timing will range between top dead center to slightly retarded providing optimum starting.

When starting a warm engine, the rpm is higher which results in slightly advanced timing.

If the engine coolant and intake air temperature is hot, the ignition timing will not be advanced reducing starter motor "load".

Based on the calculated air volume and mass the EMS2000 determines the proper amount of timing advance for the air/fuel mixture.

the EMS2000 monitors the Knock Sensors after each ignition for a normal (low) signal. If the signal value exceeds the threshold, the EMS2000 identifies the "knock" and retards the ignition timing (3°) for that cylinder the next time it is fired. This process is repeated in 3° increments until the knock ceases. the ignition timing will be advanced again in increments to just below the knock limit and maintain the timing at that point.

If a fault is detected with the Knock Sensor(s) or circuits, the EMS2000 deactivates Knock Control. the ignition timing will be set to a conservative basic setting (to reduce the risk of detonation) and a fault will be stored. the "Malfunction Indicator Light" will be illuminated when the OBD II criteria is achieved.

Waste Spark Ignition
the Waste Spark Theory of Ignition Systems is based on understanding basic electric circuits. Electricity always travels in a circuit. Electricity leaves the source, travels through conductors and a consumer and returns to the point of origin. the coil secondary winding is the source of spark for the spark plugs. the spark must return there in order for the circuit to be complete.

the plugs that fire simultaneously (1-4, and 2-3) are wired in series with the coil. Since the polarity of the coil windings is fixed, one spark plug fires in the forward direction, from the center to the outer electrode, the other plug always fires backwards or from the outer electrode to the center. the spark travels from the coil through the conductor to the spark plug, the energy remaining after the spark has jumped the gap, travels through the cylinder head, through the companion spark plug and back to the coil.

One of the spark plugs will be firing on exhaust and the other on compression. the cylinder firing on compression will consume 80-90% of the energy produced by the coil. the cylinder firing on exhaust will consume the balance.

On the MINI the secondary ignition for cylinders 1 and 4 are paired as are 2 and 3. Cylinders 3 and 4 fire in the conventional manner from the center electrode out to the outer electrode. Cylinders 1 and 2 fire from the outer electrode back to the center electrode.