1. Power Supply: The ignition coil receives power from the battery via the ignition switch. This power flows through the ignition coil's primary winding (a coil of relatively thick wire with few turns).
2. Control by the PCM (Powertrain Control Module): The PCM, the van's "computer brain," controls the timing of the spark. It does this by switching a ground to the coil's primary winding via an ignition control module (ICM) or directly depending on the specific system in your Astro van (some used a separate ICM while others integrated it into the PCM). When the PCM sends the ground signal, the circuit completes, allowing current to flow through the primary winding.
3. Magnetic Field Creation: The flow of current through the primary winding creates a magnetic field around it. This magnetic field builds up relatively slowly due to the coil's inductance.
4. Interrupting the Current: The PCM/ICM then cuts off the ground signal, abruptly stopping the current flow in the primary winding. This rapid collapse of the magnetic field is crucial.
5. Voltage Induction in the Secondary Winding: The rapid collapse of the magnetic field induces a much higher voltage in the secondary winding (a coil of much thinner wire with many more turns). This is the principle of electromagnetic induction – a changing magnetic field induces an electromotive force (voltage) in a nearby conductor. The ratio of turns in the primary to secondary windings determines the voltage multiplication.
6. High Voltage to Spark Plugs: This extremely high voltage is then routed to the spark plugs via the distributor cap and rotor (if equipped with a distributor) or directly to the spark plug wires (coil-on-plug system – COP). The high voltage jumps the gap in the spark plug, igniting the air/fuel mixture.
7. Cycle Repeats: This entire process repeats for each cylinder, with the PCM precisely timing the spark for optimal combustion.
Important Note: 1998 Astro vans might use either a distributor-based ignition system or a coil-on-plug (COP) system. In a distributor system, a single coil provides high voltage to the distributor, which then distributes it to the individual spark plugs. In a COP system, each cylinder has its own individual ignition coil mounted directly on the spark plug. The operation principle remains largely the same, but the arrangement of components differs. Knowing which system your van uses is essential for proper diagnosis and repair. You can usually determine this by looking at the engine bay.
