Description And Operation

DESCRIPTION 

Courtesy of CHRYSLER GROUP, LLC

The ignition system is comprised of the following components:

1.	Refer to IGNITION COIL .
2.	Refer to CAMSHAFT POSITION (CMP) SENSOR .
3.	Refer to IGNITION CAPACITOR .
4.	Refer to KNOCK SENSOR .
5.	Refer to VARIABLE VALVE TIME (VVT) SOLENOIDS .
6.	Refer to POWERTRAIN CONTROL MODULE (PCM) .

OPERATION 

All engines use a fixed ignition timing system. Basic ignition timing is not adjustable. All spark advance is determined by the Powertrain Control Module (PCM). The ignition system used on these engines is referred to as coil on plug. The system's four main components are the coils, spark plugs, camshaft position sensors, and the crankshaft position sensor. The coil on plug ignition system utilizes an ignition coil for every cylinder (coil over). The ignition coils are mounted directly over each spark plug.

Refer to COMPONENT INDEX .

The 3.6 liter engine uses a Dual Over Head Camshaft (DOHC) configuration. The camshafts are a nodular cast iron design and have two pressed on magnetic timing wheels that are magnetically encoded. The two CMP sensors are located at the rear of the cylinder head covers. The sensors are bolted to the cylinder head and utilize a radial lip seal where they protrude through the covers. The attaching bolt has an O-ring seal and is captured in the sensor. The CMP sensors are dual read, single element hall effect sensors mounted between the magnetic encoded timing wheels. The magnetic timing wheels are used because of their small diameter allowing for a compact cylinder head design.

Refer to COMPONENT INDEX .

An ignition coils are used with each spark plug and are mounted on the spark plug (coil over).

• The Auto Shutdown (ASD) relay provides battery voltage to the ignition coil.
• The PCM provides a ground path with an internal Low Side Driver (LSD).
• When the PCM opens the LSD, the ground path is broken and the energy in the coil primary re-energizes.
• The PCM will de-energize the ASD relay if it does not receive the crankshaft position sensor and camshaft position sensor inputs.

Refer to COMPONENT INDEX .

The coil capacitor helps dampen the amount of conducted electrical noise to the camshaft position sensor, crankshaft position sensor, and throttle position sensor. This noise is generated on the 12 volt supply wire to the ignition coils and fuel injectors. The ignition capacitor also provides a voltage to the ignition coil allowing for less ramp time when the coil is activated.

Refer to COMPONENT INDEX .

There are two knock sensors mounted under the intake manifold. Depending on the vibration frequency within the cylinder walls the sensor generates voltage proportional to it. The PCM detects the voltage value generated by the sensors rate of change, and as a function of that change, it can understand whether there is knocking in the cylinders. To reduce the knocking. The PCM starts reducing the ignition advance in order to limit the maximum pressure that can be reached in the combustion chamber. The higher the pressure the greater the risk of knocking.

When the knock sensor detects a knock in one of the cylinders on the corresponding bank, it sends an input signal to the PCM. In response, the PCM retards ignition timing for all cylinders by a scheduled amount. Knock sensors contain a piezoelectric crystal which constantly vibrates and sends an input voltage (signal) to the PCM while the engine operates. As the intensity of the crystal's vibration increases, the knock sensor output voltage also increases. The voltage signal produced by the knock sensor increases with the amplitude of vibration. The PCM receives the knock sensor voltage signal as an input. If the signal rises above a predetermined level, the PCM will store that value in memory and retard ignition timing to reduce engine knock. If the knock sensor voltage exceeds a preset value, the PCM retards ignition timing for all cylinders. It is not a selective cylinder retard. The PCM ignores knock sensor input during engine idle conditions. Once the engine speed exceeds a specified value, knock retard is allowed. Knock retard uses its own short term and long term memory program. Long term memory stores previous detonation information in its battery-backed Random Access Memory (RAM). The maximum authority that long term memory has over timing retard can be calibrated. Short term memory is allowed to retard timing up to a preset amount under all operating conditions (as long as Revolutions Per Minute (RPM) is above the minimum RPM) except at Wide Open Throttle (WOT). The PCM, using short term memory can respond quickly to retard timing when engine knock is detected. Short term memory is lost any time the ignition key is turned off.

Knock Sensor Signal: 

Courtesy of CHRYSLER GROUP, LLC

Refer to COMPONENT INDEX .

The PCM is located next to the washer solvent reservoir. The PCM is a digital computer containing a micro-controller. The PCM receives input signals from various switches and sensors that are referred to as PCM Inputs. Based on these inputs the PCM adjusts various engine and vehicle operations through devices that are referred to as PCM Outputs. The PCM uses the Controller Area Network-Chassis (CAN-C) bus to perform engine diagnostics and flash operations.

The PCM is a pre-programmed digital computer. The PCM operates the following:

• Fuel system
• Regulates ignition timing
• Air-fuel ratio
• Emission control devices
• Charging system
• Certain transmission features
• Speed control

The PCM can adapt its programming to meet changing operating conditions. It also receives input signals from various switches and sensors. Based on these inputs, the PCM regulates various engine and vehicle operations through different system components. These components are referred to as PCM Outputs.

For more information on the PCM. Refer to MODULE, POWERTRAIN CONTROL (PCM), DESCRIPTION AND OPERATION .

Refer to COMPONENT INDEX .

The 3.6L engine is equipped with VVT. This system adjusts the timing of all four camshafts independently using solenoids and oil control valves to direct oil pressure into the camshaft phaser assemblies. The camshaft phaser assembly advances and/or retards camshaft timing to improve engine performance, mid-range torque, idle quality, fuel economy, and reduce emissions. The four VVT solenoids are located on the front of the cylinder head covers. The pintle should move freely within the solenoid body. Do not attempt to disassemble the solenoids, they are not serviceable. The solenoids are identical but should be installed in the same location as removed. Camshaft phaser position is adjusted using regulated oil pressure through an Oil Control Valve (OCV). To begin phaser movement, the PCM applies a pulse-width modulated voltage signal to the VVT solenoid to extend or retract the solenoid pintle. The pintle pushes against an internal spool valve within the OCV moving the valve forwards and backwards to direct oil flow. The position of the spool inside the OCV determines which ports and chambers inside the phaser are being fed, either to advance the timing of the phaser sprocket relative to the camshaft, retard it, or hold a desired position.