For 1990-2009 cars

The electronic ignition (EI) system consists of the following components and wiring circuits:

• | The ignition control (IC) module

• | The ignition coils

• | The powertrain control module (PCM)

• | The 24X crankshaft position (CKP) sensor

• | The 7X CKP sensor

• | The camshaft position (CMP) sensor

The EI wiring circuits listed here use the following service common names. Between the IC module and the PCM:

• | Low resolution engine speed signal

• | IC timing control

• | IC timing signal

• | Low reference

Between the 7X CKP sensor and the IC module:

• | CKP sensor (1) signal

• | Low reference

Between the 24X CKP sensor and the PCM:

• | Medium resolution engine speed signal

• | 12-volt reference

• | Low reference

Between the CMP and the PCM:

• | CMP sensor signal

• | Low reference

• | 12-volt reference

The IC module also receives power and chassis ground through the following circuits:

• | Ignition 1 voltage

• | Ground

### Purpose

The 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 to provide optimal performance, fuel economy, and control of exhaust emissions.

### Operation

In this EI system there is one coil for each pair of cylinders. Each pair is at top dead center (TDC) at the same time, and 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 coil is triggered both 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 producing a very high energy spark. This is known as waste spark ignition.

### EI Component Description

The following is a list of ignition system components and their functions.

### 24X CKP Sensor and Interrupter Ring

The 24X crankshaft position (CKP) sensor (1), secured in a mounting bracket (3) and bolted to the front side of the engine timing chain cover (2), is partially behind the crankshaft balancer. The crankshaft balancer contains the 24X CKP sensor interrupter ring.

The 24X CKP sensor contains a hall-effect switch. A hall-effect switch is a solid state switching device, which produces an OFF-ON pulse when a rotating element passes between the sensor tip and a magnet. This rotating element is called an interrupter ring. In this case the interrupter ring has 24 evenly spaced blades and windows. This sensor produces 24 ON-OFF signal pulses per crankshaft revolution. The 24X signal is used for enhanced smoothness and idle stability at a lower calibrated RPM. The 24X signal is known as the medium resolution engine speed signal.

The 7X CKP sensor is bolted into the center of the engine block and protrudes into the crankcase. The 7X CKP sensor reluctor wheel is cast into the crankshaft.

The 7X CKP sensor is a variable reluctance sensor. The magnetic field of the sensor is altered by a reluctor wheel that has seven machined slots, six of which are equally spaced 60 degrees apart. The seventh slot is spaced 10 degrees from one of the other slots. The 7X CKP sensor produces six pulses and one sync pulse for each revolution of the crankshaft. This signal must be present for the IC module to send a 3X reference signal to the PCM. The 3X reference is known as the low resolution engine speed signal.

### Camshaft Position (CMP) Sensor

The camshaft position (CMP) sensor is a hall effect sensor which is triggered by a magnet pressed into the camshaft sprocket. The CMP sensor provides a signal pulse once every camshaft revolution, known as the CMP sensor signal. The IC module uses this signal to identify the position of the #1 cylinder at top dead center.

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

Three dual tower ignition coils are mounted to the IC module, and are serviced individually. The IC module performs the following functions:

• | It receives and processes the signals from the 7X CKP sensor.

• | It determines the correct coil triggering sequence. This coil sequencing occurs at start-up, and is remembered by the IC module. After the engine is running, the module will continue to trigger the coils in the correct sequence.

• | It determines the correct direction of the crankshaft rotation, and cuts spark and fuel delivery to prevent backfiring if this condition occurs.

• | It produces and sends low resolution engine speed signals to the PCM.

#### Powertrain Control (PCM) Module

The powertrain control module (PCM) is responsible for maintaining proper spark and fuel injection timing for all driving conditions. Ignition control (IC) spark timing is the method the PCM uses to control spark advance and ignition dwell. To provide optimum driveability and emissions, the PCM monitors input signals from the following components in calculating ignition control (IC) spark timing:

• | Ignition control (IC) module

• | Engine coolant temperature (ECT) sensor

• | Intake air temperature (IAT) sensor

• | Mass air flow (MAF) sensor

• | Internal Mode or PNP inputs from Internal Mode switch or Park/Neutral position switch

• | Throttle position (TP) sensor

• | Vehicle speed sensor (VSS), or transmission output speed sensor (TOSS)

The following describes the PCM to IC module circuits:

• | Low resolution engine speed--PCM input--From the ignition control module, the PCM uses this signal to calculate engine RPM and crankshaft position. The PCM also uses the pulses on this circuit to initiate injector operation.

• | Low reference--PCM input--This is a ground circuit for the digital RPM counter inside the PCM, but the wire is connected to engine ground only through the IC module. This circuit assures there is no ground drop between the PCM and IC module.

• | IC timing signal--PCM output--The IC module controls spark timing while the engine is cranking. This is called bypass mode. Once the PCM receives low resolution engine speed signals from the IC module, the PCM applies 5 volts to the IC timing signal circuit allowing the IC module to switch spark control to PCM control.

• | IC timing control--PCM output--The IC output circuitry of the PCM sends out timing signals to the IC module on this circuit. When in the Bypass Mode, the IC module grounds these signals. When in the IC Mode, the signals are sent to the IC module to control coil dwell and spark timing. Proper sequencing of the ignition coils is always controlled by the IC module.

### Ignition System Modes of Operation

Anytime the PCM does not apply 5 volts to the IC timing signal circuit, the IC module controls ignition by triggering each coil in the proper sequence at a pre-determined dwell. This is called Bypass Mode ignition used during cranking and running below a certain RPM, or during a default mode due to a system failure.

When the PCM begins receiving 24X reference and 3X reference pulses, the PCM applies 5 volts to the IC timing signal circuit. This signals the IC module to allow the PCM to control the dwell and spark timing. This is IC Mode ignition. During IC Mode, the PCM compensates for all driving conditions. If the IC mode changes due to a system fault, it will stay in default until the ignition is cycled OFF to ON, or the fault is no longer present.

### Ignition System Service

Special care must be taken when diagnosing and handling EI systems. The secondary voltage output can exceed 40,000 volts. Refer to the applicable diagnosis or repair section for more information.