Ignition System: Description and Operation

INTRODUCTION
The Owner's Manual also contains maintenance information.

SYSTEM OPERATION
Ignition System
The ignition systems used on the 3.9L V-6, the 5.2L V-8 and the 5.9L V-8 are basically identical. Similarities and differences between the systems will be discussed.
The ignition system is controlled by the powertrain control module (PCM) on all engines.
The ignition system consists of:
- Spark Plugs
- Ignition Coil
- Secondary Ignition Cables
- Distributor (contains rotor and camshaft position sensor)
- Powertrain Control Module (PCM)
- Crankshaft Position, Camshaft Position, Throttle Position and MAP Sensor.

Powertrain Control Module

Powertrain Control Module (PCM):

The Powertrain Control Module (PCM) is located in the engine compartment.
The ignition system is controlled by the PCM.

NOTE: Base ignition timing by rotation of distributor is not adjustable.

The PCM opens and closes the ignition coil ground circuit to operate the ignition coil. This is done to adjust ignition timing, both initial (base) and advance, and for changing engine operating conditions.
The amount of electronic spark advance provided by the PCM is determined by five input factors: engine coolant temperature, engine rpm, intake manifold temperature, manifold absolute pressure and throttle position.

Distributor

Distribution And Camshaft Position Sensor - Typical:

All 3.9L V-6 and 5.2L/5.9L V-8 engines are equipped with a conventional camshaft driven mechanical distributor containing a shift driven distributor rotor. The distributor is equipped with the camshaft position (fuel sync) sensor. This sensor provides fuel injection synchronization and cylinder identification.

The distributor does not have built in centrifugal or vacuum assisted advance. Base ignition timing and all timing advance is controlled by the Powertrain Control Module (PCM). Because ignition timing is controlled by the PCM, base ignition timing is not adjustable.

The distributor is held to the engine in the conventional method using a hold down clamp and bolt. Although the distributor can be rotated, it will have no effect on ignition timing.

All distributors contain an internal oil seal that prevents oil from entering the distributor housing. The seal is not serviceable.

Spark Plugs
All engines use resistor type spark plugs. Remove the spark plugs and examine them for burned electrodes and fouled, cracked or broken porcelain insulators. Keep plugs arranged in the order in which they were removed from the engine. A single plug displaying an abnormal condition indicates that a problem exists in the corresponding cylinder.

Spark plugs that have low milage may be cleaned and reused if not otherwise defective, carbon or oil fouled. Refer to Spark Plug/Testing and Inspection.

Spark Plug Cables
Spark plug cables are sometimes referred to as secondary ignition wires. These cables transfer electrical current from the ignition coil(8) and/or distributor, to individual spark plugs at each cylinder. The resistive spark plug cables are of nonmetallic construction. The cables provide suppression of radio frequency emissions from the ignition system.

Ignition Coil
Battery voltage is supplied to the ignition coil positive terminal from the ASD relay.

The Powertrain Control Module (PCM) opens and closes the ignition coil ground circuit for ignition coil operation.

Base ignition timing is not adjustable on any engine. By controlling the coil ground circuit, the PCM is able to set the base timing and adjust the ignition timing advance. This is done to meet changing engine operating conditions.

The ignition coil is not oil filled. The windings are embedded in an epoxy compound. This provides heat and vibration resistance that allows the ignition coil to be mounted on the engine.

Automatic Shutdown (ASD) Relay
As one of its functions, the ASD relay will supply battery voltage to the ignition coil. The ground circuit for the ASD relay is controlled by the Powertrain Control Module (PCM). The PCM regulates ASD relay operation by switching the ground circuit on-and-off.

Crankshaft Position Sensor-3.9L V-6 Engine

Sensor Operation:

Engine speed and crankshaft position are provided through the crankshaft position sensor. The sensor generates pulses that are the input sent to the Powertrain Control Module (PCM). The PCM interprets the sensor input to determine the crankshaft position. The PCM then uses this position, along with other inputs, to determine injector sequence and ignition timing.

The sensor is a hall effect device combined with an internal magnet. It is also sensitive to steel within a certain distance from it.

On 5.2L and 5.9L V-8 engines, the flywheel/drive plate has 8 single notches, spaced every 45 degrees, at its outer edge.

The notches cause a pulse to be generated when they pass under the sensor. The pulses are the input to the PCM. For each engine revolution, there are 8 pulses generated on V-8 engines.

The engine will not operate if the PCM does not receive a crankshaft position sensor input.

Camshaft Position Sensor
The camshaft position sensor is located in the distributor on all engines.

The sensor contains a hall effect device called a sync signal generator to generate a fuel sync signal. This sync signal generator detects a rotating pulse ring (shutter) on the distributor shaft. The pulse ring rotates 180 degrees through the sync signal generator. Its signal is used in conjunction with the crankshaft position sensor to differentiate between fuel injection and spark events. It is also used to synchronize the fuel injectors with their respective cylinders.

When the leading edge of the pulse ring (shutter) enters the sync signal generator, the following occurs: The interruption of magnetic field causes the voltage to switch high resulting in a sync signal of approximately 5 volts.

When the trailing edge of the pulse ring (shutter) leaves the sync signal generator, the following occurs: The change of the magnetic field causes the sync signal voltage to switch low to 0 volts.

Ignition Switch And Key Lock Cylinder
The ignition switch is located on the steering column. The Key-In-Switch is located in the ignition switch module. For electrical diagnosis of the Key-In-Switch, For removal/installation of either the key lock cylinder or ignition switch, refer to Ignition Switch and Key Cylinder Replacement.

On vehicles equipped with an automatic transmission and a steering column mounted shifter, an interlock device is located within the steering column. This interlock device is used to lock the transmission shifter in the PARK position when the key is in the LOCKED or ACCESSORY position. The interlock device within the steering column is not serviceable. If repair is necessary, the steering column assembly must be replaced.

On vehicles equipped with an automatic transmission and a floor mounted shifter, a cable connects the interlock device within the steering column assembly, to the transmission floor shift lever. This interlock device is used to lock the transmission shifter in the PARK position when the key is in the LOCKED or ACCESSORY position. The interlock device within the steering column is not serviceable. If repair is necessary, the steering column assembly must be replaced. The shifter interlock cable can be adjusted or replaced.