Ignition System: Description and Operation
INTRODUCTIONThis information describes the ignition Systems for all engines.
The 3.9L V-6 and 5.2L V-8 engines will be referred to 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.
On Board Diagnostics is described in Emission Control Systems. The Owner's Manual also contains maintenance information.
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.
The ignition system is controlled by the PCM.
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.
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 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:
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 (ECT) sensor
- The Crankshaft Position (CKP) sensor (engine speed)
- The Manifold Absolute Pressure (MAP) sensor
- The Throttle Position Sensor (TPS)
- Transmission gear selection
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 - 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 - 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 Removal/Installation.
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.