Ignition System: Description and Operation
IGNITION SYSTEMThe 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 Sensor, Camshaft Position Sensor, Throttle Position Sensor and MAP Sensor.
IGNITION SYSTEM
The ignition system used 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.
SPARK PLUGS
This engine uses inductive type spark plugs.
Spark plug resistance values range from 6000 to 20,000 ohms (when checked with at least a 1000 volt spark plug tester). Do not use an ohmmeter to check the resistance values of the spark plugs. Inaccurate readings will result.
To prevent possible pre-ignition and/or mechanical engine damage, the correct type/heat range/number spark plug must be used.
Always use the recommended torque when tightening spark plugs. Incorrect torque can distort the spark plug and change plug gap. It can also pull the plug threads and do possible damage to both the spark plug and the cylinder head.
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. Also refer to Spark Plug Conditions.
CAUTION: Never use a motorized wire wheel brush to clean the spark plugs. Metallic deposits will remain on the spark plug insulator and will cause plug misfire.
SPARK PLUG CABLES
Spark plug cables are sometimes referred to as secondary ignition wires.
The spark plug 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:
IGNITION COIL PACKS
Two separate coil packs containing a total of five independent coils are attached to a common mounting bracket. They are 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.
Battery voltage is supplied to all of the ignition coils positive terminals from the ASD relay. If the PCM does not see a signal from the crankshaft and camshaft sensors (indicating the ignition key is ON but the engine is not running), it will shut down the ASD circuit.
Base ignition timing is not adjustable on the 8.0L V-10 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 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
CKP Sensor Location:
CRANKSHAFT POSITION SENSOR
The Crankshaft Position (CKP) sensor is located on the right-lower side of the cylinder block, forward of the right engine mount, just above the oil pan rail.
CKP Sensor Operation:
The Crankshaft Position (CKP) 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.
CMP Sensor Location:
CAMSHAFT POSITION SENSOR
The Camshaft Position (CMP) sensor is located on the timing chain case/cover on the left-front side of the engine.
The CMP 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.
CMP 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 electrical ignition switch is located on the steering column. It is used as the main on/off switching device for most electrical components. The mechanical key lock cylinder is used to engage/disengage the electrical ignition switch.
Vehicles equipped with an automatic transmission and a floor mounted shifter:
A cable is used to connect the interlock device in 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 lock cylinder is rotated to 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.
If the ignition key is difficult to rotate to or from the LOCK or ACCESSORY position, it may not be the fault of the key cylinder or the steering column components. The brake transmission shift interlock cable may be out of adjustment.
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 lock cylinder is in the LOCKED or ACCESSORY position. If it is difficult to rotate the key to or from the LOCK or ACCESSORY position, the interlock device within the steering column may be defective. This device is not serviceable. If repair is necessary, the steering column assembly must be replaced.
Vehicles equipped with a manual transmission, a floor mounted shifter, and a LEVER below the ignition key:
A lever is located on the steering column behind the ignition key lock cylinder. The lever must be manually operated to allow rotation of the ignition key lock cylinder to the LOCK or ACCESSORY position. If it is difficult to rotate the key to the LOCK or ACCESSORY position, the lever mechanism may be defective. This mechanism is not serviceable. If repair is necessary, the steering column assembly must be replaced.
Vehicles equipped with a manual transmission, a floor mounted shifter, and NO LEVER below the ignition key:
The ignition key cylinder must be depressed to allow it to be rotated into the LOCK or ACCESSORY position. If it is difficult to rotate the key to the LOCK or ACCESSORY position, the lock mechanism within the steering column may be defective. This mechanism is not serviceable. If repair is necessary, the steering column assembly must be replaced.