Ignition Control

The primary function of the EI module is to charge and discharge the coil packs based on PCM control. The PCM has two control circuits, one for the 2/3 coil and the other for the 1/4 coil. The PCM uses a high control signal of near 5 volts to charge up the coil and a low control signal of near 0 volts to discharge the coil. If the coil is charged and the control signal is low, the coil will fire through its secondary towers. The secondary voltage can reach a maximum of 40,000 volts.

The secondary current always travels in the same direction and in a series type circuit. For example, when the PCM fires the 1/4 coil, the current will flow out of the #1 coil tower, to the #1 spark plug wire, to the #1 spark plug, through the block, up through the #4 spark plug, though the #4 spark plug wire and back to the #4 coil tower. If one of the wires/plugs were to open, the other mating cylinder would still fire out of its coil tower because the circuit would be completed through the EI module bolts.

In order to determine when to fire a cylinder, the PCM uses the Crankshaft Position (CKP) sensor. The crankshaft has 7 machined notches, 2 of which are close together representing a double pulse. The PCM uses this double pulse to identify cylinder #4 Top Dead Center (TDC). However, the PCM still has to identify whether cylinder #4 is on TDC compression or TDC exhaust. This is accomplished by the use of Compression Sense Ignition.