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 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. If equipped with the coil on plug ignition system it utilizes an ignition coil for every cylinder, it is mounted directly over the each spark plug.
OPERATION - IGNITION SYSTEM
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 SENSOR-CAMSHAFT POSITION and Crankshaft Position Sensor.
OPERATION
The glow plugs are used to preheat the combustion chambers in order to achieve the ignition temperature required for the fuel-air mixture.
The glow plug consists of a housing with a female thread and an interference-fit rod. The heating element is integrated in the glow rod. It consists of a heating winding and a control winding connected in series.
When the glow plug system is switched "ON", a current of about 30 ampere flows to each glow plug. The heating winding heats the glow plug. The control winding increases its resistance as the temperature rises and limits the current to approximately 15-25 ampere. The glow plug is protected this way from overloads.
DESCRIPTION
There are two glow plug relays. These relays are located in the Power Distribution Center (PDC) in the engine compartment.
When the ignition (key) switch is place in the ON position, a signal is sent to the ECM relating current engine coolant temperature. This signal is sent from the engine coolant temperature sensor.
After receiving this signal, the ECM will determine if, when and for how long of a period the glow plug relays should be activated. This is done before, during and after the engine is started. Whenever the glow plug relays are activated, it will control the 12 volt 100 amp circuit for the operation of the four glow plugs. Each relay control two glow plugs.
The Glow Plug lamp is tied to this circuit. Lamp operation is also controlled by the ECM.
With a cold engine, the glow plug relays and glow plugs may be activated for a maximum time of 200 seconds. Refer to the following Glow Plug Control chart for a temperature/time comparison of the glow plug relay operation.
In this chart, Pre-Heat and Post-Heat times are mentioned. Pre-Heat is the amount of time the glow plug relay control circuit is activated when the ignition (key) is switched ON, without the engine running. Post-Heat is the amount of time the glow plug relay control circuit is activated after the engine is operated. The Glow Plug lamp will not be activated during the post-heat cycle.
| Engine Coolant Temperature "Key ON" | Wait-To Start Lamp "ON" (Seconds) | Pre-Heat Cycle (Glow Plugs On Seconds) | Post-Heat Cycle (Seconds) |
|---|---|---|---|
| 30C | 20 SEC. | 35 SEC. | 200 SEC. |
| 10C | 8 SEC. | 23 SEC. | 180 SEC. |
| +10C | 6 SEC. | 21 SEC. | 160 SEC. |
| +30C | 5 SEC. | 20 SEC. | 140 SEC. |
| +40C | 4 SEC. | 19 SEC. | 70 SEC. |
| +70C | 1 SEC. | 16 SEC. | 20 SEC. |
DESCRIPTION - PLATINUM PLUGS
The V6 engines use platinum resistor spark plugs. They have resistance values of 6,000 to 20,000 ohms when checked with at least a 1000 volt tester. For spark plug identification and specifications, Refer to SPECIFICATIONS .
Do not use an ohm meter to check the resistance of the spark plugs. This will give an inaccurate reading.
When the spark plugs use a single or double platinum tips and they have a recommended service life of 100,000 miles for normal driving conditions per schedule A in this article. The spark plugs have a recommended service life of 75,000 miles for severe driving conditions per schedule B in this article. A thin platinum pad is welded to both or just the center electrode end(s). (Scheme 21) Extreme care must be used to prevent spark plug cross threading, mis-gapping and ceramic insulator damage during plug removal and installation. see scheme 80
Scheme 19
| 1 - APPLY ANTI-SEIZE COMPOUND HERE ONLY |
|---|
| 2 - PLATINUM SPARK SURFACE |
| CAUTION | Cleaning of the platinum plug may damage the platinum tip. |
Scheme 20
| 1 - TAPER GAUGE |
Scheme 21
Always remove the ignition coil assembly by grasping at the spark plug boot, turning the assembly 1/2 turn and pulling straight back in a steady motion.
- Disconnect the negative battery cable.
- Remove the intake manifold, «(Refer to ENGINE/MANIFOLDS/INTAKE MANIFOLD - REMOVAL)»(ref-255938-S39869547212007060500000) .
- Prior to removing the ignition coils, spray compressed air around the coil area and spark plug or contaminates from spark plug tube. On 3.5L engines, it is necessary to loosen the screws by alternating back and forth. Do not lose the spacers under the coil when loosening the screws.
- Remove the ignitions coil.
- Remove the spark plug using a quality socket with a rubber or foam insert.
- Inspect the spark plug condition.