Ignition System: Description and Operation
INTRODUCTIONThe 3.9L V-6 and 5.2L V-8 engines will be referred to in this Ignition Group as: Light Duty Cycle (LDC) engines. The 5.9L V-8 gas powered engine will be referred to as either: Light Duty Cycle (LDC) or Heavy Duty Cycle (HDC) engines. The 8.0L V-10 engine will be referred to as either: Medium Duty Cycle (MDC) or Heavy Duty Cycle (HDC) engines.
Either of the HDC gas powered engines can be easily identified by the use of an engine mounted air injection pump. The 3.9L V-6 engine, the 5.2/5.9L V-8 LDC or the 8.0L V-10 MDC gas engines will not use an air injection pump.
SYSTEM OPERATION
Ignition System-V-6/V-8 engines
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)
- Also to be considered part of the ignition system are certain inputs from the Crankshaft Position, Camshaft Position, Throttle Position and MAP Sensors
Ignition System-8.0L V-10 Engine
The ignition system used on the 8.0L V-10 engine does not use a conventional mechanical distributor. The system will be referred to as a distributor-less ignition system. The ignition coils are individually fired, but each coil is a dual output. Refer to Ignition Coil Pack for additional information.
The ignition system is controlled by the powertrain control module (PCM) on all engines.
The ignition system consists of:
- Spark Plugs
- Ignition Coil Packs containing individual coils
- Secondary Ignition Cables
- Powertrain Control Module (PCM)
- Also to be considered part of the ignition system are certain inputs from the Crankshaft Position, Camshaft Position, Throttle Position and MAP Sensors.
Powertrain Control Module
Powertrain Control Module (PCM):
The Powertrain Control Module (PCM) is located in the engine compartment.
NOTE: On 3.9L/5.2L/5.9L engines, base ignition timing by rotation of distributor is not adjustable.
The PCM opens and closes the ignition coil ground circuit (or circuits) to operate the ignition coil (or coil packs). 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
Distributor 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 shaft 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 holddown 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
The 3.9L V-6 and 5.2L (5.9L V-8 engines use resistor type spark plugs. The 8.0L V-10 engine uses inductive 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 mileage may be cleaned and reused if not otherwise defective, carbon or oil fouled. Refer to the Spark Plug Condition.
Spark Plug Cables
Spark plug cables are sometimes referred to as secondary ignition wires. These cables transfer electrical current from the ignition coil(s) 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-3.9L/5.2L/5.9L Engines
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.
Ignition Coil Packs-8.0L Engine
The ignition system used on the 8.0L V-10 engine does not use a conventional mechanical distributor. It will be referred to as a distributor-less ignition system. Ignition timing is not adjustable on any 8.0L V-10 engine.
Ignition Coil Packs - V-10 Engine:
Two separate coil packs containing a total of five independent coils are attached to a common mounting bracket located above the right engine valve cover. The coil packs are not oil filled. The front coil pack contains three independent epoxy filled coils. The rear coil pack contains two independent epoxy filled coils.
When one of the 5 independent coils discharges, it fires two paired cylinders at the same time (one cylinder on compression stroke and the other cylinder on exhaust stroke).
Coil firing is paired together on cylinders:
- Number 5 and 10
- Number 9 and 8
- Number 1 and 6
- Number 7 and 4
- Number 3 and 2
The ignition system is controlled by the powertrain control module (PCM) on all engines. The PCM was formerly referred to as the SBEC or engine controller.
The automatic shutdown (ASD) relay, after receiving signals from the crankshaft and camshaft position sensors, will supply battery voltage to all of the ignition coil positive terminals. If these signals are not received by the PCM after approximately one second of engine cranking (start-up), the ASD relay will shut off positive voltage to all of the coils. Coil operation (firing) is then controlled by switching ground circuits (off-and-on) through the PCM. The PCM will determine cylinder identification after receiving signals from the crankshaft and camshaft position sensors.
The PCM adjusts ignition timing based on inputs it receives from:
- The engine coolant temperature sensor
- The crankshaft position sensor (engine speed)
- The manifold absolute pressure (MAP) sensor
- The throttle position sensor
- Transmission gear selection
Automatic Shutdown (ASD) Relay-3.9L/ 5.2L/5.9L Engines
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.
Automatic Shutdown (ASD) Relay-8.0L V-10 Engine
As one of its functions, the ASD relay will supply battery voltage to each of the 5 independent ignition coils. 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
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.
Sensor Operation:
The flywheel/drive plate has groups of notches at its outer edge. On 3.9L V-6 engines, there are three sets of double notches and three sets of single notches.
The notches cause a pulse to be generated when they pass under the sensor. The pulses are the input to the PCM.
The engine will not operate if the PCM does not receive a crankshaft position sensor input.
Crankshaft Position Sensor-5.2L/5.9L V-8 Engines
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.
Sensor Operation:
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.
Crankshaft Position Sensor - 8.0L V-10 Engine
Crankshaft Position Sensor Location:
The crankshaft position sensor is located on the right-lower side of the cylinder block, forward of the right engine mount, just above the oil pan rail.
Crankshaft Position Sensor Operation:
The crankshaft position sensor detects notches machined into the middle of the crankshaft.
There are five sets of notches. Each set contains two notches. Basic ignition timing is determined by the position of the last notch in each set of notches. Once the powertrain control module (PCM) senses the last notch, it will determine crankshaft position (which piston will next be at Top Dead Center). An input from the camshaft position sensor is also needed. It may take the module up to one complete engine revolution to determine crankshaft position during engine cranking.
The PCM uses the signal from the camshaft position sensor to determine fuel injector sequence. Once crankshaft position has been determined, the PCM begins energizing a ground circuit to each fuel injector to provide injector operation.
Camshaft Position Sensor-3.9L/5.2L/5.9L Engines
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.
Camshaft Position Sensor-8.0L V-10 Engine
Camshaft Position Sensor Location:
The camshaft position sensor is located on the timing chain case/cover on the left-front side of the engine.
The camshaft position sensor 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. The sensor generates electrical pulses. These pulses (signals) are sent to the powertrain control module (PCM). The PCM will then determine crankshaft position from both the camshaft position sensor and crankshaft position sensor.
Sensor Operation:
A low and high area are machined into the camshaft drive gear. The sensor is positioned in the timing gear cover so that a small air gap exists between the face of sensor and the high machined area of cam gear.
When the cam gear is rotating, the sensor will detect the machined low area. Input voltage from the sensor to the PCM will then switch from a low (approximately 0.3 volts) to a high (approximately 5 volts). When the sensor detects the high machined area, the input voltage switches back low to approximately 0.3 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 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, a cable connects an 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 is not serviceable. If repair is necessary, the steering column assembly must be replaced. The shifter interlock cable can be adjusted or replaced.