Ignition Coil: Description and Operation

IGNITION COIL - PCM OUTPUT

Ignition Coil Pack:

The coil pack assembly consists of 2 coils molded together. The coil pack is mounted on the valve cover.

WARNING: THE DIRECT IGNITION SYSTEM GENERATES APPROXIMATELY 40,000 VOLTS. PERSONAL INJURY COULD RESULT FROM CONTACT WITH THIS SYSTEM.

High tension leads route to each cylinder from the coil. The coil fires two spark plugs every power-stroke. One plug is the cylinder under compression, the other cylinder fires on the exhaust stroke. Coil number one fires cylinders 1 and 4. Coil number two fires cylinders 2 and 3. The PCM determines which of the coils to charge and fire at the correct time.

The Auto Shutdown (ASD) relay provides battery voltage to the ignition coil. The PCM provides a ground contact (circuit) for energizing the coil. When the PCM breaks the contact, the energy in the coil primary transfers to the secondary causing the spark. The PCM will de-energize the ASD relay if it does not receive the crankshaft position sensor and camshaft position sensor inputs. Refer to Auto Shutdown (ASD) Relay - PCM Output for relay operation.

Base timing is non-adjustable, but is set from the factory at approximately 10 BTDC when the engine is warm and idling.

There is an adaptive dwell strategy that runs dwell from 4 - 6 msec when engine speed is below 3000 rpm and battery voltage is 12 - 14 volts. During cranking, dwell can be as much as 200 msec. The adaptive dwell is driven by the sensed current flow through the injector drivers. Current flow is limited to 8 amps.

The low resistance of the primary coils can allow current flow in excess of 15 amps. The PCM has a current sensing device in the coil output circuit. As dwell time starts, the PCM allows current to flow. When the sensing device registers 8 amps, the PCM begins to regulate current flow to maintain and not exceed 8 amps through the remainder of the dwell time. This prevents the PCM from being damaged by excess current flow.