Engine Ignition (Description and Operation)

The ignition coil (12029), which is mounted on the upper intake manifold, can be described as a coil pack containing three separate coil units. Each coil unit is individually controlled by the powertrain control module (PCM) (12A650) through separate wire leads. Each coil unit activates two spark plugs wired in a series by the spark plug wires (12286).

• One spark plug activates on the compression stroke and uses the majority of the ignition coil's stored energy.
• The other spark plug activates on the exhaust stroke and uses very little of the ignition coil's stored energy.
• Because the pairs of spark plugs are connected in a series, one spark will travel from ground to the electrode while the other spark will travel from the electrode to ground.

The spark plug (12405):

• changes the high voltage pulse into a spark which ignites the fuel and air mixture.
• originally equipped on the vehicle has a platinum-enhanced active electrode for long life.

The crankshaft position (CKP) sensor (6C315):

NOTE: Initial engine ignition timing is set at 10 degrees +- 2 degrees before top dead center (BTDC) and is not adjustable.

• is a variable reluctance sensor triggered by a 36-minus-1 tooth trigger pulse wheel located on the crankshaft (6303) inside the engine front cover (6019).

The sine wave type signal generated from the crankshaft position sensor provides two types of information:

• position of the crankshaft in 10 degree increments
• the crankshaft speed (rpm)

The powertrain control module (PCM) (12A650) uses this information to determine ignition coil turn ON and turn OFF times and misfire detection.

Engine Ignition (DIAGNOSIS AND TESTING)

Refer to the Powertrain Control/Emissions Diagnosis (PC/ED) manual.