Ignition System: Description and Operation

Engine Ignition






The 4.0L (push rod) engine ignition system consists of the:

- Crankshaft position (CKP) sensor (6C315).
- ignition coil (12029).
- spark plug wire (12286).
- spark plugs (12405).

The ignition system:

- is an electronic ignition (EI) system controlled by an electronic engine control integrated into the powertrain control module (PCM) (12A650).
- base timing is set at 10 degrees before top dead center (BTDC) and is not adjustable.

The crankshaft position sensor:

- is a variable reluctance sensor.
- senses a missing tooth on crankshaft damper pulse ring.
- generates a crankshaft position signal which is sent to the powertrain control module. The PCM counts this signal for engine rpm.

The ignition coil:

- changes low voltage pulses from the powertrain control module to high voltage pulses.
- has three transformers.

The spark plug wires carry high voltage pulses from the ignition coil to the spark plugs.

The spark plugs:

- change high voltage pulses into spark at the gap, which ignites the fuel and air mixture.
- have a platinum-enhanced active electrode for long life. The active electrode is different for LH and RH sides.
- have replacements (with both electrodes platinum-enhanced) so they can be used on either side.