Ignition Coils

by Bob O’Neill and Bob Lincoln

To fire the spark plugs, a high voltage is needed to jump the gap in the plug.  The ignition coil is a transformer which takes a 12v input on the primary winding. When this input is suddenly dropped to zero, the second winding discharges a large voltage to the distributor. The distributor distributes the high voltage to the proper spark plug by way of a rotor which is turned by the distributor shaft. The rotor connects the input (high voltage) to the proper plug wire as the rotor passes the spark plug lead.

(Newer cars without distributors use a "coil pack" or, even more recently, a coil for each individual spark plug. These work under the same principles but without a distributor; a signal is provided by the logic module itself without the many moving parts of a distributor.)

The 12v supplied to the primary winding of the coil goes through the ASD relay and is grounded by the power module. The driver circuit in the power module is switched on and off by the logic module, which manages spark timing. When the proper timing is achieved, it shuts off the power module driver, removing the ground to the coil, which generates the high voltage for the spark.

As the logic module manages the coil driver, it monitors the output of the output transistor. When it does not sense 0 volts when the circuit is on or 12v when the circuit is off, it triggers a code 43 and the engine stalls.

Coil packs and coil-on-plug

While the 2.2 and 2.5 liter engines had a single coil (like the slant six and V8s before them), the 3.3 liter engine and later engines (including the Neon 2.0) used a coil pack (later, individual coils would be placed on top of the spark plugs — “coil-on-plug” ignition). The Neon had four coils, one per cylinder.

The 3.3 liter V6 was used on the Dynasty, as well as other cars and minivans; it remains in use in 2008. The early 3.3 liter V6 had three coils, each one working for two cylinders. The computer sent out three timing signals, one per coil; when one plug fired to ignite fuel, the “companion plug” fired during the exhaust cycle, with no significant consequences. Going to one coil per cylinder eliminated that extra spark.

LINKS: Stalling | ASD relay | Spark plugs | Code 43

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