For 1990-2009 cars

### Electronic Ignition (EI) System Operation

The electronic ignition (EI) system produces and controls the high energy secondary spark. This spark ignites the compressed air/fuel mixture at precisely the correct time, providing optimal performance, fuel economy, and control of exhaust emissions. The engine control module (ECM) primarily collects information from the crankshaft position (CKP) and camshaft position (CMP) sensors to control the sequence, dwell, and timing of the spark.

### Crankshaft Position (CKP) Sensor

The crankshaft position (CKP) sensor circuits consist of an engine control module (ECM) supplied 5-volt reference circuit, a low reference circuit, and an output signal circuit. The CKP sensor is an internally magnetic biased digital output integrated circuit sensing device. The sensor detects magnetic flux changes of the teeth and slots of a 58-tooth reluctor wheel on the crankshaft. Each tooth on the reluctor wheel is spaced at 60-tooth spacing, with 2 missing teeth for the reference gap. The CKP sensor produces an ON/OFF DC voltage of varying frequency, with 58 output pulses per crankshaft revolution. The frequency of the CKP sensor output depends on the velocity of the crankshaft. The CKP sensor sends a digital signal, which represents an image of the crankshaft reluctor wheel, to the ECM as each tooth on the wheel rotates past the CKP sensor. The ECM uses each CKP signal pulse to determine crankshaft speed and decodes the crankshaft reluctor wheel reference gap to identify crankshaft position. This information is then used to determine the optimum ignition and injection points of the engine. The ECM also uses CKP sensor output information to determine the camshaft relative position to the crankshaft, to control camshaft phasing, and to detect cylinder misfire.

### Crankshaft Reluctor Wheel

The crankshaft reluctor wheel is part of the crankshaft. The reluctor wheel consists of 58 teeth and a reference gap. Each tooth on the reluctor wheel is spaced 6 degrees apart with a 12-degree space for the reference gap. The pulse from the reference gap is known as the sync pulse. The sync pulse is used to synchronize the coil firing sequence with the crankshaft position, while the other teeth provide cylinder location during a revolution.

### Camshaft Position (CMP) Sensor

The camshaft position (CMP) sensor is a hall ignition control (IC) type sensor. The sensor is true power on (TPO) at power up, which means it is capable of recognizing whether it is in front of a tooth or a notch at power up, and to set its output accordingly. The sensor is a high technology product that integrates a self calibrating system that compensates for environmental changes, such as temperature and air gap. The sensor is composed of a magneto-electronic module that generates a magnetic signal and transforms it into a digital signal. The sensor operates in 2 functional modes. The first mode is the static functional mode. This mode is valid at sensor power up. In this mode, the sensor behaves like a simple DC hall IC switch with 2 fixed switching points. The static functional mode is active during the first 10 mechanical edges of the reluctor wheel and as long as the signal frequency is lower than 1.2 Hertz, plus or minus 0.5 Hertz, with the one tooth reluctor wheel. When the signal frequency exceeds the previous mentioned limit, the sensor switches to the second functional mode, the self-calibrating functional mode. This mode enables the sensor to reach high angular position accuracy, which is not possible to achieve in the static functional mode. In the self-calibrating mode, the sensor acts as a field induction sensor, which is more accurate at higher engine RPM. The sensor switches from self-calibrating mode to static functional mode when the signal frequency becomes lower than 0.3 Hertz, plus or minus 0.1 Hertz, with the 1-tooth reluctor wheel. When the sensor switches back from self-calibrating mode to the TPO mode, a pulse of short duration is generated on the sensor output signal. The pulse may occur on the low signal state or on the high signal state.

The CMP sensor wiring consists of a 12-volt reference circuit, a low reference circuit, and a signal circuit. The CMP sensors work in conjunction with a 1-tooth reluctor wheel on the exhaust CMP actuators. The CMP sensors work in conjunction with an 8-tooth reluctor wheel on the intake CMP actuators. As each tooth on the reluctor wheel passes the CMP sensor it sends a digital signal, which is an image of the wheel, to the engine control module (ECM). The ECM processes this information to determine the exact position of the camshafts, and to determine the optimum ignition and injection points of the engine.

### Camshaft Reluctor Wheels

The camshaft reluctor wheel is part of the camshaft position (CMP) actuator. This system consists of 2 different reluctor wheels. One for the exhaust camshafts on bank 1 and bank 2 and the other for the intake camshafts on bank 1 and bank 2. The reluctor wheel on the exhaust CMP actuators has one tooth that extends 175 degrees around the circumference of the wheel. The reluctor wheel on the intake CMP actuators is an 8-tooth wheel that consists of 4 long and 4 short high and low phases. The 8X reluctor wheel is also used for the limp home mode.

### Ignition Coil/Module

Each ignition coil/module has the following circuits:

• | An ignition voltage circuit

• | A ground

• | An ignition control (IC) circuit

• | A low reference circuit

The engine control module (ECM) controls the individual coils by transmitting timing pulses on the IC circuit of each ignition coil/module to enable a spark event.

The spark plugs are connected to each coil by a short boot. The boot contains a spring that conducts the spark energy from the coil to the spark plug. The spark plug electrode is tipped with platinum for long wear and higher efficiency.

### Engine Control Module (ECM)

The engine control module (ECM) controls all ignition system functions, and constantly corrects the spark timing. The ECM monitors information from various sensor inputs that include the following:

• | The throttle position (TP) sensor

• | The engine coolant temperature (ECT) sensor

• | The mass air flow (MAF) sensor

• | The intake air temperature (IAT) sensor

• | The vehicle speed sensor (VSS)

• | The transmission gear position or range information sensors

• | The engine knock sensor (KS)

### Modes of Operation

During normal operation the engine control module (ECM) controls all ignition functions. If either the crankshaft position (CKP) or camshaft position (CMP) sensor signal is lost, the engine will continue to run because the ECM will default to a limp home mode using the remaining sensor input. Each coil is internally protected against damage from excessive voltage. If one or more coils were to fail in this manner, a misfiring condition would result. Diagnostic trouble codes are available to accurately diagnose the ignition system with a scan tool.