Ignition Control

The primary function of the EI module is to charge and discharge the coil packs based on ECM control. The ECM has two control circuits, one for the 2/3 coil and the other for the 1/4 coil. The ECM 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 across the spark plug can reach a maximum of 37,000 volts.

The secondary current for a coil always travels in the same direction and in a series type circuit. For example, when the ECM fires the 1/4 coil, the current will flow out of the # 1 coil tower, to the # 1 spark plug boot, to the # 1 spark plug, through the block, up through the # 4 spark plug, though the # 4 spark plug boot and back to the # 4 coil tower. Therefore, when a coil fires, both cylinders tied to it fire simultaneously. If one of the boots/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 ECM uses the signal from the Crankshaft Position (CKP) sensor. The crankshaft has 7 machined notches, 2 of which are close together representing a double pulse. The ECM uses this double pulse to identify cylinder # 4 Top Dead Center (TDC). However, the ECM still has to identify the position of the camshaft in order to initiate sequential fuel injection. This is accomplished by the use of Compression Sense Ignition.