Ignition System: Description and Operation

IGNITION SYSTEM

NOTE: 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 distributorless ignition system used on these engines is referred to as the Direct Ignition System (DIS). The system's three main components are the coils, crankshaft position sensor, and camshaft position sensor.

The crankshaft position sensor and camshaft position sensor are hall effect devices. The camshaft position sensor and crankshaft position sensor generate pulses that are inputs to the PCM. The PCM determines engine position from these sensors. The PCM calculates injector sequence and ignition timing from crankshaft & camshaft position. For a description of both sensors, refer to Camshaft Position Sensor and Crankshaft Position Sensor.

CAMSHAFT POSITION SENSOR

Fig. 1 Camshaft Position Sensor Location:

The camshaft position sensor is mounted in the front of the timing case cover. The bottom of the sensor is positioned in front of the camshaft sprocket.

Fig. 2 Camshaft Position Sensor:

The camshaft position sensor provides cylinder identification to the Powertrain Control Module (PCM). The sensor generates pulses. The PCM determines crankshaft position from the camshaft position sensor and crankshaft position sensor inputs. The PCM uses the input to determine fuel injection synchronization and to determine which ignition coil to energize.

Fig. 3 Camshaft Sprocket:

The camshaft position sensor detects when a step in the camshaft sprocket passes beneath it. When the sensor detects the step, the input voltage from the sensor to the PCM switches from low (0.3 volts) to high (5 volts). As the step returns away from the sensor, the input voltage switches back to low (0.3 volts). The paper spacer is not used on Viper. Don't use at all it plugs up the Oil pickup screen.

IGNITION COIL

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

Fig. 7 Ignition Coil Pack (Right Side):

Fig. 8 Ignition Coil Pack (Left Side):

The electronic ignition system uses two epoxy filled coil packs mounted on a bracket at the rear of the engine. The coil pack on the left side, contains three separate coils and fires cylinders 1, 2, 3, 4, 6, and 7. The coil pack on the right side, contains two individual coils and fires cylinders 5, 8, 9, and 10. When one of the coils discharges, it fires two cylinders at the same time (one cylinder on its compression stroke, the other on its exhaust stroke).

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.

SPARK PLUG
This engine uses resistor spark plugs. They have resistance values of 6,000 to 20,000 ohms when checked with at least a 1000 volt tester.

Remove the spark plugs and examine them for burned electrodes and fouled, cracked or broken porcelain insulators. Keep plugs arranged in the order in which they were removed from the engine. An isolated plug displaying an abnormal condition indicates that a problem exists in the corresponding cylinder.

Fig. 12 Setting Spark Plug Electrode Gap - Typical:

Spark plugs that have low mileage may be cleaned and reused if not otherwise defective. Adjust the gap between the electrodes to the dimensions specified in the chart at the end of this section.

Always tighten spark plugs to the specified torque. Over tightening can cause distortion resulting in a change in the spark plug gap. Tighten spark plugs to 27 Nm (20 ft. lbs.) torque.

SPARK PLUG CABLE
Spark Plug cables are sometimes referred to as secondary ignition wires. The wires transfer electrical current from the electronic ignition coils to the individual spark plug at each cylinder. The nonmetallic spark plug cables have built in resistance. The cables provide suppression of radio frequency emissions from the ignition system.

Check the spark plug cable connections for good contact at the coil or coil pack and distributor cap towers and at the spark plugs. Terminals should be fully seated. The nipples and spark plug covers should be in good condition. Nipples should fit tightly on the coil or coil pack and distributor cap towers and spark plug cover should fit tight around spark plug insulators. Loose cable connections can cause ignition malfunctions by permitting water to enter the towers, corroding, and increasing resistance. To maintain proper sealing at the terminal connections, the connections should not be broken unless testing indicates high resistance, an open circuit or other damage.

Clean high tension cables with a cloth moistened with a non-flammable solvent and wipe dry. Check for brittle or cracked insulation. Plastic clips in various locations protect the cables from damage. When the cables are replaced the clips must be used to prevent damage to the cables.