Ignition Coil: Description and Operation

PURPOSE
The ignition coil pack is a component of the ignition system that is used to produce a voltage strong enough to jump the spark plug gap and ignite the air/fuel mixture under all operating conditions.

CONSTRUCTION
The coil pack consists of three epoxy filled ignition coils molded together in one pack.

Each ignition coil consists of a primary winding, a secondary winding, and a soft iron core. The windings are embedded in an epoxy compound to protect the coil from vibration damage.

The primary windings are made up of 2-3 hundred turns of heavy gauge wire, over the secondary windings. The secondary windings are made up of 30-40 thousand turns of light gauge wire around a soft iron core.

OPERATION
Power is supplied to the positive side of coils by the auto shutdown (ASD) relay. Switching of the negative coil ground is controlled by the Powertrain Control Module (PCM) through the ASD relay.

When the PCM grounds primary circuit, current flows through the primary windings, and a magnetic field is produced. As the magnetic field builds it is concentrated in the soft iron core.

When the PCM opens the primary circuit ground from each coil, the magnetic field collapses. As the field collapses it passes through each turn of the secondary windings, producing a small voltage in each turn. The voltage in each turn is multiplied by the number of wire turns.

The PCM will de-energize the ASD relay if it does not receive the crankshaft and camshaft position sensor inputs.

Each coil fires two spark plugs on each power stroke. One coil fires the cylinder under compression, the other fire on the exhaust stroke.

CIRCUIT OPERATION
Circuit A14 is connected to the BUS bar in the Power Distribution Center (PDC). and connects to battery voltage. The contact side of the Automatic Shut Down (ASD) relay connects circuits A14 and A142. A 20 Amp fuse, in cavity B of the PDC, protects circuits A14 and A142.

Circuit A14 also supplies voltage to the coil side of the ASD relay. The Powertrain Control Module (PCM) controls the ground path for the coil side of the ASD relay on circuit K51. Circuit K51 connects to cavity 67 of the PCM.

Circuit A142 supplies voltage for the ignition coil pack. The coil pack consists of three individual coils molded together. The PCM controls the ground circuit of each coil.
- Circuit K17 is the ground circuit for the ignition coil that fires spark plugs #1 and #4. Circuit K17 connects to cavity 3 of the PCM.
- Circuit K18 is the ground circuit for the ignition coil that tires spark plugs #3 and #6. Circuit K18 connects to cavity 2 of the PCM.
- Circuit K19 is the ground circuit for the ignition coil that tires spark plugs #2 and #5. Circuit K19 connects to cavity 11 of the PCM.

The ground circuit wires for the coils are wrapped in a helical shield, which is used for noise suppression. Grounding for the shield is provided in two places. The first is the ground eyelet located on the engine and the second is at the right headlamp ground located at the right front frame rail.