Ignition System: Description and Operation

All ignition systems include a battery, a distributor, an engine control switch, spark plugs, and the primary and secondary wiring.

DISTRIBUTOR
A distributor with a separate coil is used on the 3.1L V6 engine. The coil connects to the rotor through a high tension wire.
The distributor uses a magnetic pickup assembly located inside the distributor which contains a permanent magnet, a pole piece with internal teeth, and pickup coil. When the teeth of the timer core rotating inside the pole piece line up with the teeth of the pole piece, an induced voltage in the pickup coil signals the electronic module to trigger the coil primary circuit.

The primary current decreases and a high voltage of up to 35,000 volts is induced in the ignition coil secondary winding which is directed through the rotor and secondary leads to fire the spark plugs. The capacitor in the distributor is for radio noise suppression.
The distributor also features a longer spark duration, made possible by the higher amount of energy stored in the coil primary. This is desirable for firing lean mixtures.
No periodic lubrication is required. Engine oil lubricates the lower bushing and an oil-filled reservoir provides lubrication for the upper bushing.

IGNITION CONTROL (IC) SYSTEM
IC is part of most Computer Command Control systems. The computer, called an Engine Control Module (ECM), monitors information from various engine sensors, computes the desirable spark timing, and signals the distributor to change the timing.
The distributor does not contain centrifugal advance weights, springs, or a vacuum advance unit.
For information on the IC system, system components and their locations, and diagnostic charts, refer to the "Driveability and Emissions".

KNOCK SENSOR (KS)
The 3.1L engine is equipped with KS. A KS is mounted in the engine block. It is connected by a blue wire to the KS control module, mounted on the front fender in the engine compartment or bracket mounted on the block. The sensor, in response to engine knock, sends a signal to the module. This sends a signal to the ECM, located in the passenger compartment. The ECM sends a signal to the distributor to retard spark timing. For information and diagnostic material on KS, refer to "Driveability and Emissions".

IGNITION TIMING
Timing specifications are listed on the Vehicle Emissions Control Information label on the engine hood. Always follow Vehicle Emissions Control Information label procedures when adjusting timing. When using a timing light, connect an adapter between the No. 1 spark plug and the No. 1 spark plug wire, or use an inductive type pickup. Do not pierce the plug lead. Once the insulation of the spark plug cable has been broken, voltage will jump to the nearest ground, and the spark plug will not fire properly.
Some engines incorporate a magnetic timing probe hole for use with special electronic timing equipment. Consult manufacturer's instructions for use of this equipment.

SPARK PLUG WIRES
The 7 mm (0.276 in.) wire used on the 3.1L V6 engine has an outer layer of silicone. The silicone spark plug boots form a tight seal on the plugs. Refer to "Spark Plug Wiring and Boots" later in this section for service precautions.

SPARK PLUGS
Resistor type, tapered seat spark plugs are used. No gasket is used on these tapered seat plugs. Refer to below for an explanation of letter coding on spark plugs. A dot before the spark plug code or the letter "C" after the number in the code indicates the plug has a copper core. Refer to the "Vehicle Emissions Control Information" label on the engine hood for correct gap information.
Normal or average service is assumed to be a mixture of idling, slow speed, and high speed operation with some of each making up the daily total driving. Occasional or intermittent high-speed driving is essential to good spark combustion heat that burns away any excess deposits of carbon or oxide that may have accumulated from frequent idling or continual stop-and-go or slow-speed driving. Spark plugs are protected by an insulating boot made of special heat-resistant material which covers the spark plug terminal and extends downward over a portion of the plug insulator. These boots prevent flash-over with resultant missing of engine, even though a film is allowed to accumulate on the exposed portion of plug porcelains.
Do not mistake corona discharge for flash-over or a shorted insulator. Corona is steady blue light appearing around the insulator, just above the shell crimp. It is the visible evidence of a high-tension field, and has no effect on ignition performance. Usually it can be detected only in darkness. This discharge may repel dust particles, leaving a clear ring on the insulator just above the shell. This ring is sometimes mistakenly regarded as evidence that combustion gases have blown out between shell and insulator.

Numbers relate to thread size as follows:
1st number denotes THREAD SIZE
4=14mm
8=18mm
10=10mm
12=12mm

2=1/2-inch taper
5=1/2-inch
6=3/4-inch
7=7/8-inch

2nd number denotes HEAT RANGE

0-1-2-3-4-5-6-7-8-9
COLD ............ HOT