For 1990-2009 cars

### Electronic Ignition (EI) System Operation

The electronic ignition (EI) system produces and controls the high energy 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 CKP sensor is connected to the ECM by the following circuits:

• | 5-volt reference

• | Low reference

• | Signal

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 rotational 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, along with information from the CMP sensors is then used to determine the optimum ignition and fuel 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 CMP sensors are triggered by a notched reluctor wheels built onto the intake and the exhaust camshaft sprockets. Both of the CMP sensors provide four signal pulses every camshaft revolution. Each notch, or feature of the reluctor wheel is of a different size which is used to identify the compression stroke of each cylinder and to enable sequential fuel injection. Both of the CMP sensors are connected to the ECM by the following circuits:

• | 5-volt reference

• | Low reference

• | Signal

### Ignition Coil/Module

Each ignition coil/module has the following circuits:

• | Ignition voltage

• | Ground

• | Ignition control (IC)

• | Low reference

The ECM controls the individual ignition coil/modules 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 ECM controls all of the ignition system functions, and constantly corrects the spark timing. The ECM monitors information from various sensor inputs that include the following:

• | Throttle position (TP) sensor

• | Engine coolant temperature (ECT) sensor

• | Mass air flow (MAF) sensor

• | Intake air temperature (IAT) sensor

• | Vehicle speed sensor (VSS)

• | Engine knock sensor (KS)

• | Manifold absolute pressure (MAP) sensor

• | Intake air pressure and temperature sensor

### Modes of Operation

During normal operation the ECM controls all of the ignition system functions. If the CKP or either CMP sensor signals are lost, the engine will continue to run because the ECM will default to a limp home mode using the remaining sensor input. Each of the ignition coil/modules are internally protected against damage from excessive voltage. If one or more ignition coil/modules were to fail, a misfiring condition would result. Diagnostic trouble codes are available to accurately diagnose the ignition system with a scan tool.