How The Circuit Works
The 4.6L engine uses an Electronic Ignition System. This system does not have a conventional distributor and spark timing cannot be adjusted.
Voltage is present at the PCM Power Relay contacts at all times through the EEC/VRCM Fuse.
With the Ignition Switch in RUN, voltage is present at the Left and Right Ignition Coil Packs. Voltage is also present at the PCM Power Relay coil through the PCM Diode and the Relay coil is energized. The Relay contacts close and current flows through the EEC/VRCM Fuse and the PCM Power Relay to the Powertrain Control Module (PCM) and the Ignition Control Module (ICM).
During engine cranking (and after the engine starts), the Crankshaft Position (CKP) Sensor sends an AC voltage signal to the ICM. The signal provides the ICM with crankshaft position (in 10 degree increments) and engine speed.
The ICM processes this signal, generates a Profile Ignition Pickup (PIP) signal, and sends it to pin 56 of the PCM. Using this signal and information provided by other engine control sensors, the PCM determines the appropriate ignition timing. The PCM then outputs (at pin 36) a Spark Output (SPOUT) timing signal to the ICM.
The ICM turns the appropriate Ignition Coil primary circuit on and off at the instant necessary to achieve the correct dwell and spark timing by intermittently grounding circuits 95 (T/W), 96 (T/O), 97 (T/LG) and 98 (T/LB). Each interruption of primary current makes that Ignition Coil secondary circuit produce a high voltage pulse. Coil #1 provides spark for cylinders #1 and #6; coil #2 services cylinders #3 and #5; coil #3 services cylinders #4 and #7, and coil #4 services cylinders #2 and #8.
High tension wires apply the high voltage pulses directly to the spark plugs.
The ICM also generates an Ignition Diagnostic Monitor (IDM) signal, which the PCM monitors to detect ignition system faults.
