Ignition Control Module, theory of operation '97 2.2 OHV - Performance Forum

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Ignition Control Module, theory of operation '97 2.2 OHV
Monday, May 20, 2013 1:05 PM
I'm trying to get a better understanding of how the Ignition Control Module operates on a '97 Cavalier, 2.2 OHV engine. I have read the information in the factory manuals, but they don't go into the detail I'm looking for. Here is my understanding of the system. Please correct any inaccuracies, and confirm any correct statements.

1. The Crankshaft Position Sensor (CKS) is a variable reluctor and generates a signal seven times per crankshaft revolution.
2. The signal from the CKS is sent to the Ignition Control Module (ICM). The ICM converts the signal from the CKS to a 5 volt square wave signal - the 7x signal.
3. The 7x signal from the ICM is sent to the Power Control Module(PCM). The PCM uses the signals from the other engine management sensors (MAP, IAT, CLT, etc) to determine when to fire each of the two ignition coils (wasted spark).
4. The PCM fires each of the two ignition coils by lifting (opening) the ground side of the primary winding of each coil.
5. When the field from the primary winding of the ignition coil collapses, a high voltage current is developed in the secondary windings of the ignition coil that creates a spark at the spark plug.

In short: The CKS sends a signal to the ICM. The ICM converts that signal to a 5 volt square wave that is sent to the PCM. The PCM then triggers the ignition coil directly at the proper time. The role of the ICM is only to condition the signal from the CKS for the PCM. The ICM does not come between the PCM and the ignition coil, except to provide a connection to +12 V and the PCM.

Thanks in advance.

Re: Ignition Control Module, theory of operation '97 2.2 OHV
Tuesday, June 11, 2013 5:12 AM
Unfortunately, I never received a response on this post, but here's a little bit of follow up.

Through trial and error, I determined that the signal from the PCM triggers a circuit within the ICM that in turn fires the ignition coils. The signal from the PCM will not directly fire a coil (like the Neon ignition coil) that does not include an additional trigger circuit.
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