Ignition Control - Service Information: Overview Dodge Nitro I

DESCRIPTION

The ignition system is controlled by the Powertrain Control Module (PCM) on all engines.

This engine uses a separate ignition coil for each cylinder. The one-piece coil bolts directly to the cylinder head. Rubber boots seal the secondary terminal ends of the coils to the top of all 6 spark plugs. A separate electrical connector is used for each coil.

Because of coil design, spark plug cables (secondary cables) are not used. A distributor is not used with the 4.0L engine.

One knock sensor is used to help control spark knock.

The Auto Shutdown (ASD) relay provides battery voltage to each ignition coil.

The ignition system consists of

1. 6 Spark Plugs
2. 6 Separate Ignition Coils
3. 1 Knock Sensor
4. Powertrain Control Module (PCM)
5. Also to be considered part of the ignition system are certain inputs from the Crankshaft Position, Camshaft Position, knock and MAP Sensors

OPERATION - 3.7L

Two knock sensors are used; one for each cylinder bank. When the knock sensor detects a knock in one of the cylinders on the corresponding bank, it sends an input signal to the Powertrain Control Module (PCM). In response, the PCM retards ignition timing for all cylinders by a scheduled amount.

Knock sensors contain a piezoelectric material 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 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 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.

Note. Over or under tightening the sensor mounting bolts will affect knock sensor performance, possibly causing improper spark control. Always use the specified torque when installing the knock sensors.

OPERATION - 4.0L

Only one knock sensor is used. When the knock sensor detects a knock in one of the cylinders, it sends an input signal to the Powertrain Control Module (PCM). In response, the PCM retards ignition timing for all cylinders by a scheduled amount.

Knock sensors contain a piezoelectric material 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 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 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.

Note. Over or under tightening the sensor mounting bolt will affect knock sensor performance, possibly causing improper spark control. Always use the specified torque when installing the knock sensor.

Scheme 10

Only one sensor (1) is used with the 4.0L engine. It is attached to the top of the cylinder block below the intake manifold.

1. Remove intake manifold. Refer to «REMOVAL»(ref-306143-S33795118172008120900000) .
2. Disconnect knock sensor pigtail harness from engine wiring harness. This connection is made near front of engine (3).
3. Remove sensor mounting bolt (2). Note foam strip on bolt threads. This foam is used only to retain the bolt to sensor for plant assembly. It is not used as a sealant. Do not apply any adhesive, sealant or thread locking compound to this bolt.
4. Remove sensor from engine.

Scheme 11

The two knock sensors (1) are bolted into the cylinder block under the intake manifold. The two sensors share a common wiring harness using one electrical connector (3). Because of this, they must be replaced as a pair.

Note. The left sensor is identified by an identification tag (LEFT) (2). It is also identified by a larger bolt head. The Powertrain Control Module (PCM) must have and know the correct sensor left/right positions. Do not mix the sensor locations.

1. Remove intake manifold. Refer to «INSTALLATION»(ref-306142-S30306992222008120900000) - 3.7L.
2. Disconnect knock sensor dual pigtail harness from engine wiring harness. This connection is made near rear of engine.
3. Remove both sensor mounting bolts. Note foam strip on bolt threads. This foam is used only to retain the bolts to sensors for plant assembly. It is not used as a sealant. Do not apply any adhesive, sealant or thread locking compound to these bolts.
4. Remove sensors from engine.

Spark plugs cables are not used with either the 3.7L or 4.0L V-6 engines.

Scheme 12

The ignition switch (5) is located on the steering column (4). It is used as the main on/off switching device for most electrical components. The mechanical key cylinder is used to engage/disengage the electrical ignition switch.