The ignition system used on the 4.6L engine is an Electronic Distributorless Ignition System (EDIS) known as the high data rate ignition system. The EDIS eliminates the need for a distributor by using multiple ignition coils. Each coil fires 2 spark plugs at the same time. The plugs are paired so as one fires during the compression cycle, the other fires during the exhaust stroke. The next time the coil is fired, the plug that was on exhaust will be on compression and the one that was on compression will be on exhaust. The spark in the exhaust cylinder is wasted but little of the coil energy is lost. The ignition coils are mounted together in coil packs. There are 2 coil packs used, each containing 2 ignition coils.
The EDIS consists of the following components: crankshaft sensor, ignition module, ignition coil pack, the spark angle portion of the Powertrain Control Module (PCM) and the related wiring. On 1996 and later models, the engines utilize what is known as an integrated ignition system in which the Powertrain Control Module (PCM) performs all the control functions and the Ignition control Module (ICM) is eliminated.
See Figure 1
The system operates as follows: The CKP sensor produces a signal generated from the induced voltage created as the trigger wheel on the crankshaft or flywheel passes the sensor. The CKP signal provides engine position and rpm information. This signal is received at the ICM or PCM as a Profile Ignition Pickup (PIP) signal. The ICM or PCM processes the PIP signal along with signals received from other sensors on engine speed, engine temperature, and engine load, and determines the correct ignition timing and grounds the proper ignition coils in the coil pack or the individual coils. When the ignition coil is grounded, an Ignition Diagnostic Monitor (IDM) signal is sent to the ICM or PCM. This signal provides the ICM or PCM with diagnostic information and confirms that the coil fired and is also used to operate the vehicle's tachometer (if equipped).