The 8.0L engine uses a distributorless ignition system. The main components of this ignition system are:
The PCM automatically regulates the spark advance to fire the spark plugs according to input from various engine sensors. The input signals are then used to compute the optimum ignition timing for the lowest exhaust emissions and best driveability. During the crank-start period, ignition timing advance is set to ensure quick and efficient starting.
The amount of electronic spark advance provided is determined by four input factors: coolant temperature, engine rpm, throttle position and available manifold vacuum. On some systems, intake manifold temperature is also used. Gear selection may also be a factor.
Two separate coil packs, containing a total of five (5) independent ignition coils, are located on a common mounting bracket above the right side engine valve cover.
Each coil fires two cylinders simultaneously. When this occurs, one of the cylinders will be on the power stroke; the other will be on the exhaust stroke, the resulting spark being a waste spark. It is important to note that isolating one lead of the pair will eliminate the spark at both plugs.
Cylinders are paired as follows: 5/10, 9/8 for the rearmost four plug coil pack; 1/6, 7/4, 3/2 for the front six plug coil pack.
Battery voltage is supplied to each coil's positive terminal by the Automatic Shutdown (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.
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 conditions.
Base ignition timing is set by the PCM and is not adjustable.