For 1990-2009 cars

The electronic ignition (EI) system produces and controls 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 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 its compression stroke is called the event cylinder. The cylinder that is at TDC of its exhaust stroke is called the waste cylinder. When the ignition 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 ignition coils and ignition control module (ICM) are contained within one assembly. The ignition coil/ICM assembly is mounted in the center of the engine camshaft cover, with short boots connecting the ignition coils to the spark plugs. The ignition coil driver modules within the ICM are commanded ON/OFF by the powertrain control module (PCM). The EI system consists of the following components:

### Crankshaft Reluctor Wheel

The crankshaft reluctor wheel is part of the crankshaft. The reluctor wheel has seven machined notches, six of which are equally spaced 60 degrees apart. The seventh notch is spaced 10 degrees after one of the 60-degree notches. The 10-degree notch is used to synchronize the engine position, while the other notches are used to provide cylinder location during a revolution.

### Crankshaft Position (CKP) Sensor

The crankshaft position (CKP) sensor is a permanent magnet generator, known as a variable reluctance sensor. The CKP sensor produces an AC voltage of different amplitude and frequency. The frequency depends on the velocity of the crankshaft. The AC voltage output depends on the crankshaft position and the battery voltage. The CKP sensor works in conjunction with a 7X reluctor wheel attached to the crankshaft. The CKP sensor produces 7 pulses for each revolution of the crankshaft. The pulse from the 10-degree notch is known as the sync pulse. The sync pulse is used to synchronize the coil firing sequence with the crankshaft position. The CKP sensor is used for ignition timing, the fuel injector timing, misfire diagnostics and tachometer display. The CKP sensor is connected to the ECM by a signal circuit and a low reference circuit.

### Ignition Control Module (ICM) and Ignition Coils

(1) | Ignition Control Module (ICM)
(2) | Compression Sense Ignition (CSI) Pickup
(3) | Not Used
(4) | 2-3 Coil Control
(5) | Ignition Voltage
(6) | 1-4 Coil Control
(7) | Not Used
(8) | Interconnect

The powertrain control module (PCM) supplies a signal on each of the ignition control (IC) timing control circuits to the ignition control module (ICM). The ICM fires the correct ignition coil at the correct time based on the signals. The ICM detects if cylinder 1 or cylinder 3 is on the compression stroke by sensing the secondary voltage and polarity of each side of the ignition coil. The ICM detects this voltage with sensing circuitry integrated into each ignition coil. The higher voltage is on the compressing cylinder. This is called compression sense ignition. The ICM provides a synthesized cam signal to the PCM based on these inputs. The PCM uses the cam signal to synchronize fuel injection.

This system consists of the following circuits:

• | An ignition voltage circuit

• | A ground circuit

• | A camshaft position (CMP) sensor signal circuit

• | An IC timing control circuit for cylinders #1 and #4

• | An IC timing control B circuit for cylinders #2 and #3

### Powertrain Control Module (PCM)

The PCM controls all ignition system functions, and constantly corrects the spark timing. The PCM monitors information from various sensor inputs that include the following:

• | The throttle position (TP) sensor

• | The engine coolant temperature (ECT) sensor

• | The intake air temperature (IAT) sensor

• | The vehicle speed sensor (VSS)

• | The transmission gear position or range information sensors

• | The engine knock sensors (KS)

### Modes of Operation

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