System Circuits

The electronic ignition (El) system contains input/output circuits and controls two, two-tower coils, each coil firing two spark plugs. The following describes the circuits and components circuits of the EI system.


Power Input
The power input (B+) is tied to the ignition switch (12 volts nominal) and is fed through the ignition switch and EIS fuse.

Electronic Ignition Module
The electronic ignition (EI) module's primary function is to charge up the coil pack upon control of the PCM and to utilize compression sense ignition (CSI) to determine when #4 cylinder has fired on compression. The El module has incorporated circuitry to determine cylinder 4 compression by the use of capacitive pickup plates located under the 1/4 coil. Since each tower on a coil is of opposite voltage polarity and the waste spark event will generally fire before the compression event, the module can determine the polarity sequence. When the module sees a polarity sequence of positive to negative (negative being the high voltage spike), the module will then supply a ground to the number 4 signal wire, signaling to the PCM cylinder 4 has fired on compression. The use of compression sense ignition synchronizes the SFI fuel timing.

Electronic Ignition (EI) Interface
The PCM supplies two signals to the electronic ignition module. One signal is an ignition timing waveform. The falling edge of the timing waveform indicates the beginning of the spark event. The timing waveform is a 0 to 5 volt variable duty-cycle, and frequency, based on the engine waveform and is generated by the PCM to indicate spark advance.

Powertrain Control Module
The powertrain control module (PCM) controls spark dwell, spark advance and the tachometer reference signal to the I/P cluster. All spark advance and retard conditions are controlled only by the PCM at all times.

Secondary Towers
The secondary signal is a high voltage (up to 40,000 volts) timed signal, routed by way of the secondary wires to the spark plugs.



System Inputs
The EI module does not receive a signal from the crankshaft position sensor. Instead the CPK sensor signal is being received and processed by the PCM. The El module does, however, contain circuitry to determine camshaft position without using a camshaft sensor, by use of compression sense ignition (CSI). The CSI circuitry makes use of the characteristics of a waste spark ignition system, while monitoring a sequence of spark plug gap breakdown events. Capacitive pickup plates located under the 1/4 coil are used to determine whether #1 or #4 fired on a compression stroke. This capacitive sensing device is similar to inductive pickups used on engine analyzers and oscilloscopes.


Module grounding
The EI module is grounded through Pin E of the 5-pin connector. The laminated coils have an additional, redundant ground which is provided through the bolt heads to the transaxle housing. The plate on the bottom of the module is used primarily for a heat sink and has no effect on module operation.