The electronic ignition system controls fuel combustion by providing a spark to ignite the compressed air/fuel mixture at the correct time. To provide optimum engine performance, fuel economy, and control of exhaust emissions, the PCM controls the spark advance of the ignition system. Electronic ignition has the following advantages over a mechanical distributor system:

The electronic ignition system does not use the conventional distributor and coil. The ignition system consists of three ignition coils, an ignition control module, a dual Hall-effect crankshaft position sensor, an engine crankshaft balancer with interrupter rings attached to the rear, related connecting wires, and the Ignition Control (IC) and fuel metering portion of the PCM.

Conventional ignition coils have one end of the secondary winding connected to the engine ground. In this ignition system, neither end of the secondary winding is grounded. Instead, each end of a coil's secondary winding is attached to a spark plug. Each cylinder is paired with the cylinder that is opposite it (1/4, 2/5, 3/6). These two plugs are on companion cylinders, i.e., on top dead center at the same time. When the coil discharges, both plugs fire at the same time to complete the series circuit. The cylinder on compression is said to be the event cylinder and the one on exhaust is the waste cylinder. The cylinder on the exhaust stroke requires very little of the available energy to fire the spark plug. The remaining energy will be used as required by the cylinder on the compression stroke. The same process is repeated when the cylinders reverse roles. This method of ignition is called a waste spark ignition system.

Since the polarity of the ignition coil primary and secondary windings is fixed, one spark plug always fires with normal polarity and its companion plug fires with reverse polarity. This differs from a conventional ignition system that fires all the plugs with the same polarity. Because the ignition coil requires approximately 30 percent more voltage to fire a spark plug with reverse polarity, the ignition coil design is improved, with saturation time and primary current flow increased. This redesign of the system allows higher secondary voltage to be available from the ignition coils - more than 40 kilovolts (40,000 volts) at any engine RPM. The voltage required by each spark plug is determined by the polarity and the cylinder pressure. The cylinder on the compression stroke requires more voltage to fire the spark plug than the cylinder on the exhaust stroke.

It is possible for one spark plug to fire even though a plug wire from the same coil may be disconnected from its companion plug. The disconnected plug wire acts as one plate of a capacitor, with the engine being the other plate. These two capacitor plates are charged as a spark jumps across the gap of the connected spark plug. The plates are then discharged as the secondary energy is dissipated in an oscillating current across the gap of the spark plug that is still connected. Secondary voltage requirements are very high with an open spark plug or spark plug wire. The ignition coil has enough reserve energy to fire the plug that is still connected at idle, but the coil may not fire the spark plug under high engine load. A more noticeable misfire may be evident under load; both spark plugs may then be misfiring.

Crankshaft Position Sensor and Crankshaft Balancer Interrupter Rings

The dual crankshaft position sensor is secured in an aluminum mounting bracket and bolted to the front left side of the engine timing chain cover, partially behind the crankshaft balancer. A 4-wire harness connector plugs into the sensor, connecting it to the ignition control module. The dual crankshaft position sensor contains two Hall-effect switches with one shared magnet mounted between them. The magnet and each Hall-effect switch are separated by an air gap. A Hall-effect switch reacts like a solid state switch, grounding a low current signal voltage when a magnetic field is present. When the magnetic field is shielded from the switch by a piece of steel placed in the air gap between the magnet and the switch, the signal voltage is not grounded. If the piece of steel (called an interrupter) is repeatedly moved in and out of the air gap, the signal voltage will appear to go ON - OFF - ON - OFF - ON - OFF. In the case of the electronic ignition system, the piece of steel is two concentric interrupter rings mounted to the rear of the crankshaft balancer.

(1)	Crankshaft Balancer
(2)	Interrupter Rings

Each interrupter ring has blades and windows that either block the magnetic field or allow it to close one of the Hall effect switches. The outer Hall effect switch produces a signal called the CKP 18X because the outer interrupter ring has 18 evenly spaced blades and windows. The CKP 18X portion of the crankshaft position sensor produces 18 ON - OFF pulses per crankshaft revolution. The Hall-effect switch closest to the crankshaft, the CKP Sync portion of the sensor, produces a signal that approximates the inside interrupter ring. The inside interrupter ring has 3 unevenly spaced blades and windows of different widths. The CKP Sync portion of the crankshaft position sensor produces 3 different length ON - OFF pulses per crankshaft revolution. When a CKP Sync interrupter ring window is between the magnet and inner switch, the magnetic field will cause the CKP Sync Hall effect switch to ground the CKP Sync signal voltage supplied from the ignition control module. The CKP 18X interrupter ring and Hall-effect switch react similarly. The ignition control module interprets the CKP 18X and CKP Sync ON - OFF signals as an indication of crankshaft position, and the ignition control module must have both signals to fire the correct ignition coil. The ignition control module determines crankshaft position for correct ignition coil sequencing by counting how many CKP 18X signal transitions occur, i.e.; ON - OFF or OFF - ON, during a CKP Sync pulse.

Camshaft Position (CMP) Sensor

The camshaft position sensor is located on the timing cover behind the water pump near the camshaft sprocket. As the camshaft sprocket turns, a magnet in it activates the Hall effect switch in the camshaft position sensor. When the Hall-effect switch is activated, it grounds the signal line to the ICM, pulling the camshaft position sensor signal circuit's applied voltage low. This is interpreted as a CMP Sensor signal. The CMP Sensor signal is created as piston #1 is approximately 25 degrees after top dead center on the power stroke.

Ignition Control Module and Ignition Coil