Ignition system – general information
All gasoline engines are equipped with a distributorless ignition system. The ignition system consists of the battery, the ignition coil (s), the spark plug wires (3.7L and 4.7L engines), the spark plugs, a knock sensor on each cylinder head, the Camshaft Position (CMP) sensor, the Crankshaft Position (CKP) sensor, the Manifold Absolute Pressure (MAP) sensor, the Throttle Position (TP) sensor and the Powertrain Control Module (PCM). For more information about the CMP sensor, CKP sensor, knock sensors, MAP sensor, TP sensor and PCM, refer to Emissions and engine control systems. The PCM controls the base ignition timing and the ignition timing advance on all engines. The base ignition timing is not adjustable on any model.
The PCM controls the ignition system by opening and closing the ignition coil ground circuit. The computerized ignition system provides complete control of the ignition timing by determining the optimum timing in response to engine speed, coolant temperature, throttle position and vacuum pressure in the intake manifold. These parameters are relayed to the PCM by the camshaft position sensor, crankshaft position sensor, throttle position sensor, coolant temperature sensor and manifold absolute pressure sensor. The PCM and the crankshaft position sensor are very important components of the ignition system. The ignition system will not operate and the engine will not start if the PCM or the crankshaft position sensor are defective. Refer to Emissions and engine control systems for additional information on the various sensors.
3.71 V6 engine
The 3.7L V6 uses three coils, each of which is mounted on top of a spark plug of the odd-numbered cylinders. Each coil is connected to an even-numbered spark plug by a spark plug wire so that when the coil is energized, it fires both spark plugs at the same time. Only one of the two cylinders has pressure when the spark plug is fired, so it is the only cylinder that draws significant power from the coil at that time – this is a waste-spark system.
4.7L V8 engine
The 4.7L V8 engine uses a coil-over-plug system. On this engine there are eight ignition coils (each with two secondary terminals), eight spark plugs wires and 16 spark plugs. The engine has two spark plugs per cylinder, so each coil is located on top of and connected directly to one of those plugs with a rubber boot type seal and fires a spark plug at the bottom of the combustion chamber via a second high-tension terminal and a spark plug wire.
3.6L V6 and Hemi engines
The Hemi engines use a coil-over-plug system which consists of individual coils, one above each pair of spark plugs and connected directly to the spark plugs. There are no spark plug wires on these engines. Battery voltage is supplied to the ignition coil primary circuits. The PCM fires the coils in firing order sequence by turning the ground paths for their primary circuits on and off.