Ignition System: Description and Operation
IGNITION CONTROLThe ignition system used on this 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 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.
AUTOMATIC SHUT DOWN RELAY - PCM OUTPUT
The 5-pin, 12-volt, Automatic Shutdown (ASD) relay is located in the Power Distribution Center (PDC). Refer to label on PDC cover for relay location.
The ASD relay supplies battery voltage (12+ volts) to the fuel injectors and ignition coil(s). With certain emissions packages it also supplies 12-volts to the oxygen sensor heating elements.
The ground circuit for the coil within the ASD relay is controlled by the Powertrain Control Module (PCM). The PCM operates the ASD relay by switching its ground circuit ON and OFF.
The ASD relay will be shut-down, meaning the 12-volt power supply to the ASD relay will be de-activated by the PCM if: the ignition key is left in the ON position. This is if the engine has not been running for approximately 1.8 seconds there is a crankshaft position sensor signal to the PCM that is lower than pre-determined values.
ASD SENSE - PCM INPUT
A 12 volt signal at this input indicates to the PCM that the ASD has been activated. The relay is used to connect the oxygen sensor heater element, ignition coil and fuel injectors to 12 volt + power supply.
This input is used only to sense that the ASD relay is energized. If the Powertrain Control Module (PCM) does not see 12 volts at this input when the ASD should be activated, it will set a Diagnostic Trouble Code (DTC).
Fig. 5 CMP Sensor Location - 8.0L V-10 Engine:
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.
Fig. 8 CMP Sensor Operation - 8.0L V-10 Engine:
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.
Fig. 24 Ignition Coil Packs - 8.0L V-10 Engine:
IGNITION COIL
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 this 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
SPARK PLUG
The 8.0L V-10 engine uses inductive type spark plugs.
Spark plug resistance values range from 6,000 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 CABLE
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.