For 1990-2009 cars

The electronic ignition (EI) system is responsible for producing and controlling a high energy secondary spark. This spark is used to ignite the compressed air/fuel mixture at precisely the correct time. This provides optimal performance, fuel economy, and control of exhaust emissions. This ignition system uses an individual coil per cylinder. The ignition coils are mounted above each cylinder on the rocker cover with short integrated boots connecting the coils to the spark plugs. The driver modules within each ignition coil are commanded ON/OFF by the engine control module (ECM). The ECM primarily uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor to control sequence, dwell, and timing of the spark. The EI system consists of the following components:

### Crankshaft Position (CKP) Sensor

The CKP sensor is a permanent magnet generator known as a variable reluctance sensor. The CKP sensor produces an AC voltage of varying amplitude and frequency. The frequency depends on the velocity of the crankshaft. The AC output depends on the crankshaft position and the battery voltage. The CKP sensor works in conjunction with a 58 slotted reluctor wheel attached to the crankshaft. As each reluctor wheel slot rotates past the CKP sensor, the resulting change in the magnetic field creates an ON/OFF pulse 58 times per crankshaft revolution. The ECM processes the pulses to determine the crankshaft position. The ECM can synchronize the ignition timing, the fuel injector timing, and the spark knock control based on the CKP sensor and the CMP sensor inputs. Using the CKP sensor signals in conjunction with the CMP sensor signals, the ECM determines the engine position with great accuracy. The CKP sensor is also used to detect misfire and for tachometer display. The ECM learns the variations between all 58 slots under different speed and load conditions to correctly detect misfires. The CKP sensor circuits consist of a signal circuit, a low reference circuit, and a shielded ground circuit. The CKP sensor signal and low reference circuits are protected from electromagnetic interference by the shielded ground circuit.

### Crankshaft Reluctor Wheel

The crankshaft reluctor wheel is part of the crankshaft. The reluctor wheel consists of 58 slots including a reference gap. Each slot 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 slots provide cylinder location during a revolution.

### Camshaft Position (CMP) Sensor

The camshaft position (CMP) sensor is a Hall-Effect type sensor. The CMP signal is a digital ON/OFF pulse, which outputs 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 ECM to determine the position of the valve train relative to the crankshaft position. By monitoring the CMP and CKP signals, the ECM can accurately trigger the fuel injectors. This allows the ECM to calculate true sequential fuel injection mode of operation. If the CMP signal is lost while the engine is running, the fuel injection system will shift to a calculated sequential fuel injection mode based on the last fuel injection pulse, and the engine will continue to run. The CMP sensor consists of an ignition 1 voltage circuit, a low reference, and a signal circuit.

### Camshaft Reluctor Wheel

The camshaft reluctor wheel is bolted to the front of the camshaft. The wheel is a smooth track, half of which is of a lower profile than the other half. This track is read in a radial or axial fashion respectively. This allows the CMP sensor to supply a signal as soon as the key is turned ON, since the CMP sensor reads the track profile, instead of a notch.

### Ignition Coils (IC)

The ignition coil is an individual coil that directly supplies voltage to each spark plug. Each ignition coil (IC) contains a solid state driver module as its primary element. The ECM will command the IC circuit ON, this allows the current to flow through the primary coil windings for the appropriate time or dwell. When the ECM commands the IC circuit OFF, this will interrupt current flow through the primary coil windings. The magnetic field created by the primary coil windings will collapse across the secondary coil windings, which induces a high voltage. The secondary coil voltage travels from the coil output terminal, through the spark plug boot, and across the spark plug gap to the engine block. The ignition coil is not serviceable and must be replaced as an assembly. The ignition coil consists of an ignition 1 voltage circuit, an ignition control circuit, and a ground circuit.

### Engine control module (ECM)

The engine control module (ECM) is responsible for maintaining proper spark and fuel injection timing for all driving conditions. The electronic spark timing (EST) is the method the ECM uses to control spark advance. The primary coil ON/OFF is directly controlled by the ECM. To provide optimum driveability and emissions, the ECM monitors input signals from the following components in calculating ignition spark timing:

• | The crankshaft position (CKP) sensor

• | The engine coolant temperature (ECT) sensor

• | The manifold absolute pressure (MAP) sensor

• | The intake air temperature (IAT) sensor

• | The vehicle speed sensor (VSS)

• | Ambient pressure sensor (BARO)

• | The knock sensor (KS)

• | The vehicle speed sensor (VSS)

• | The mass airflow (MAF) sensor

• | The camshaft position (CMP) sensor

### Modes of Operation

There is one normal mode of operation, with the spark under the ECM control. If the CKP sensor pulses are lost the engine will not run. The loss of the CMP signal may result in a longer crank time since the ECM cannot determine which stroke the pistons are on. Diagnostic trouble codes are available to accurately diagnose the ignition system with a scan tool.

### Noteworthy Ignition Information

The ignition coils secondary output voltage is more than 30,000 volts. Avoid body contact with the ignition high voltage secondary components when the engine is running or personal injury may result.

Be careful not to damage the secondary ignition coil boots when servicing the ignition system. Rotate each spark plug wire in order to loosen the boot from the spark plug before removing. Never pierce a secondary ignition boot for any testing purposes. Future ignition system problems are guaranteed if pinpoints or test lights are pushed through the secondary ignition component insulation during testing.