Ignition Control

The primary function of the EI module is to charge and discharge each of the three primary coils individually based on ECM control. The ECM uses independent primary coil control circuits designated for each cylinder. The ECM uses a high control signal of near 5 volts to charge up the primary coil and a low control signal of near 0 volts to discharge the primary coil. If the primary coil is charged and the control signal is low, the secondary coil will fire through its secondary tower. The secondary voltage across the spark plug can reach a maximum of 40,000 volts.

In order to determine when to fire a cylinder, the ECM uses the Crankshaft Position (CKP) sensor signal in conjunction with the Camshaft Position (CMP) sensor signal to determine cylinder # 1 Top Dead Center (TDC) compression. The crankshaft has 58 machined notches with a double space between two of the notches representing cylinder # 1 TDC. The CMP sensor signal will change from a high 12 volt signal to a low 0 volt signal when cylinder # 1 is 90° before its top dead center compression stroke.