Have you checked the spark plug itself?
: Note spark plug cable original positions before removing.
- Before servicing the vehicle, refer to the precautions at the beginning of this section.
- Clean the area around the coil with compressed air.
- Remove or disconnect the following:
- Battery negative cable
- Throttle body air intake tube and intake box (if necessary)
- Coil electrical connector by moving slide lock and pressing on release lock
- Secondary high-voltage cable from coil
- Mounting bolts
- Coil from cylinder head opening by twisting
- Clean area around spark plugs with compressed air.
- Apply dielectric grease to inside of boots.
- Install or connect the following:
- Ignition coil to cylinder head opening
- 2 mounting bolts
- Torque to: 106 inch lbs. (12 Nm)
- Coil electrical connector
- Cable to coil
- Throttle body air tube and intake box (if necessary)
- Battery negative cable
Distributorless Ignition System
This vehicle uses two different types of ignition systems. The 3.7L, 4.7L, and 5.7L engines do not use a conventional distributor. The 5.9L engine uses a conventional distributor. The ignition system is controlled by the Powertrain Control Module (PCM) on all engines. Procedures in this section are for the 3.7L, 4.7L, and 5.7L engines; please see the section on Distributor Ignition Systems for procedures for the 5.9L engine.
Distributorless ignition systems (EI) are used on many current engines. This system uses the waste spark method for distributing secondary voltage. In a waste spark system, an individual coil is used to fire one pair of engine cylinders simultaneously. These cylinders are known as companions, since each of their pistons is at TDC at the same time. On a typical V6 engine for example, cylinder 1 is at TDC compression while cylinder 4 is at TDC exhaust. This is also true of cylinders 2 and 5 as well as cylinder 3 and 6.
The cylinder on the compression stroke is known as the event cylinder, while the cylinder on the exhaust stroke is called the waste cylinder. Since secondary resistance is very low in the cylinder on the exhaust stroke, little voltage is required to fire the plug. For this reason, the majority of available voltage is consumed by the cylinder on the compression stroke.
One spark plug is attached to each end of the secondary coil winding via the spark plug wires. This series circuit arrangement causes one of the plugs to fire in a forward direction (center electrode to outer electrode), and the other spark plug to fire in a reverse direction (outer electrode to center electrode). The firing voltage requirements on the waste spark ignition are significantly greater than a traditional ignition system primarily because it takes 30% more energy to fire a plug reverse polarity. When a spark plug is fired backwards, it fires from the outer electrode to the center electrode. This is a high resistance path since the electrons do not flow as easily from a cold, dull surface such as the outer electrode to a hot, sharp surface like the center electrode.
Since the coil and plugs are arranged in a series circuit, a typical plug gap of .050" results in a total gap of .100" for the whole circuit that includes two spark plugs for the companion cylinders. The waste spark can overcome this added resistance by producing high secondary output voltages due to low resistance in the primary winding. Another reason higher secondary ignition voltage is required is cylinder pressure; specifically, the lack of it. Generally, event cylinders require 10 to 12-kV to initiate current flow across the spark plug gap, while only 2 - 3-kV is needed to fire the waste cylinder. Therefore, the air gap in the waste cylinder creates no more resistance than the rotor gap does in a conventional ignition system.
There are two different methods used for coil trigger. One method sends the crankshaft sensor signal directly to the ignition module to activate the coils, while the other sends the crankshaft sensor signal to the PCM and the PCM controls ignition operation either directly or through a separate ignition module.
Waste spark ignition advantages
- It has fewer components than conventional distributor-type ignition systems.
- No mechanical adjustments to set ignition timing.
- No mechanical load (turning the distributor shaft).
- No unwanted timing variations caused by gear lash or other worn distributor components.
Another advantage of waste spark is longer coil life. To illustrate this point, consider a six-cylinder engine with conventional ignition. At 3000 RPM, the coil must fire 9000 times per minute. This is calculated by dividing the engine speed by 2, since the cam turns at half crank speed, and then multiplying the distributor RPM by the total number of engine cylinders.
In contrast, the coils on a six-cylinder engine with waste spark only work a third as hard. This is because there's a coil for every two cylinders and each coil fires every crankshaft revolution. This means that at 3000 RPM, the coils only fire 3000 times per minute. This allows each coil to operate with less dwell (time that the coil is energized), resulting in less heat buildup and longer life.
Coil Over Plug System
The coil over plug system was developed so that spark and spark timing could be better controlled on an individual cylinder basis. Each cylinder has an ignition coil mounted directly above the spark plug on the cylinder head cover. A short suppresser/connector replaces the spark plug wire and links the coil to the plug. There are different methods used for primary triggering. Some manufacturers use a combination coil/module, which means each coil has its own control circuit that is activated by the PCM. Others use remote mounted modules to trigger the coils.
Each individual coil is allowed to saturate while all other cylinders fire. For a V-8 engine, this allows a period of seven firing events for coil saturation, compared to three events for the same V-8 engine with a waste spark system. The coil over plug system also benefits from a minimum amount of energy lost, due to the resistance of spark plug wires.
Coil Near Plug System
The coil near plug system also features multiple ignition coils. An ignition coil/module is mounted in proximity of each cylinder. There is a short length of spark plug wire between the coil and the spark plug.
Each ignition coil/module has its own control circuit and is activated sequentially by the PCM. All timing decisions are made by the PCM. This includes both ignition timing and duration of the spark.