Ignition System: Description and Operation

ELECTRONIC IGNITION (EI) SYSTEM DESCRIPTION

The Electronic Ignition (EI) system is responsible for producing and controlling a high energy secondary spark. This spark is used to ignite the compressed airfuel mixture at precisely the correct time. This provides optimal performance, fuel economy, and control of exhaust emissions. This ignition system uses one coil for each pair of cylinders. Each pair of cylinders that are at Top Dead Center (TDC) at the same time are known as companion cylinders. The cylinder that is at TDC of the compression stroke is called the event cylinder. The cylinder that is at TDC of the cylinder exhaust stroke is called the waste cylinder. When the coil is triggered both companion cylinder spark plugs fire at the same time, completing a series circuit. Because the lower pressure inside the waste cylinder offers very little resistance, the event cylinder uses most of the available voltage to produce a very high energy spark. This is known as waste spark ignition. The EI system consists of the following components:

Crankshaft Position (CKP) Sensors
The Crankshaft Position (CKP) sensor contains 2 hall-effect switches in 1 housing. A hall-effect switch is a solid state switching device that produces a digital ON/OFF pulse when a rotating element passes the sensor pick-up and interrupts the sensors magnetic field. The rotating element is called an interrupter ring or blade. In this case there are two interrupter rings built into the crankshaft balancer.

The outer ring and outer switch provides the Ignition Control Module (ICM) with 18 X signals, or 18 identical pulses per crankshaft revolution. The inner ring and inner switch provides the ICM with 3 pulses per revolution, each 1 of different duration. This is called the sync pulse, each pulse represents a pair of companion cylinders. The ICM supplies a 12-volt and low reference circuit to the CKP sensor, and uses the 18 X and sync pulses to determine the crankshaft position, by counting how many ON-OFF 18 X pulses occur during a given sync pulse. With this dual interrupter ring arrangement the ICM can identify the correct pair of cylinders to fire within as little as 120 degrees of crankshaft rotation.

Camshaft Position (CMP) Sensor
The Camshaft Position (CMP) sensor signal is a digital ON/OFF pulse, output once per revolution of the camshaft. The CMP sensor does not directly affect the operation of the ignition system. The CMP sensor Information is used by the Powertrain Control Module (PCM) to determine the position of the valve train relative to the CKP. By monitoring the CMP and CKP signals the PCM can accurately time the operation of the fuel injectors. The CMP sensor shares 12-volt and low reference circuits with the CKP sensor. The CMP signal circuit is input to the ICM.