Ignition System: Description and Operation
GENERAL DESCRIPTION
The ignition circuit consists of the battery, the distributor, the ignition switch, the spark plugs, and the primary and secondary wiring.
H.E.I. DISTRIBUTOR
The High Energy Ignition distributor (HEI) is used on all engines Some engines use a distributor with an externally mounted coil. The coil connects to the rotor through a high tension wire.
The High Energy Ignition distributor with EST uses a magnetic pick-up assembly located inside the distributor which contains a permanent magnet, a pole piece with internal teeth, and pick-up 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 pick-up coil signals the electronic module to trigger the coil primary circuit. The primary current decreases and a high voltage 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.
All spark timing changes in the H.E.l. (EST) distributor are done electronically by the Electronic Control Module (ECM) which monitors information from various engine sensors, computes the desired spark timing and signals the distributor to change the timing accordingly. No vacuum or mechanical advance are used. Further EST information is found in Section 6E, Emissions.
ELECTRONIC SPARK CONTROL (ESC)
Electronic Spark Control (ESC) uses on some engines. modifies (retards) the spark advance when detonation occurs. The retard mode is held for approximately 20 seconds after which the spark control will again revert to (EST). There are three basic components in the (ESC) system.
SENSOR
The (ESC) sensor detects the presence (or absence) and intensity of detonation by the vibration characteristics of the engine. The output is an electrical signal that goes to the controller. A sensor failure would allow no retard.
DISTRIBUTOR
The Distributor is an HEI (EST) unit with an electronic module modified so it can respond to the (ESC) controller signal. This command is delayed when detonation is occurring, thus providing the level of retard required. The amount of retard is a function of the degree of detonation.
CONTROLLER
The (ESC) controller processes the sensor signal into a command signal to the distributor to adjust spark timing. The process is continuous so that the presence of detonation is monitored and controlled. The controller is a hard wired signal processor and amplifier which operates from 6 to 16 volt. Controller failure would be no ignition, no retard or full retard. The controller has no memory storage.
IGNITION TIMING
Timing specifications are listed on the Vehicle Emissions Control Information label in the engine compartment. Always follow Vehicle Emission Control Information label procedures when adjusting timing.
Some engines will4ncorporate a magnetic timing probe hole for use with special electronic timing equipment. magnetic probe hole. Consult manufacturer's instructions for use of this equipment.
SECONDARY WIRING
The spark plug wiring used with the HEI system is a carbon impregnated cord conductor encased in an 8 MM (5/ 16") diameter rubber jacket. The outer silicone jacket will withstand very high temperatures and also provide an excellent insulator for the higher voltage of the HEI system. The silicone spark plug boots form a tight seal on the plug and the boot should be twisted 1/2 turn before removing.
Care should be exercised in removing boots to avoid damage. Do not use pliers or other tools that could potentially cut and tear the silicone boot. Care should also be exercised when connecting any pick-up equipment. Do not force anything between the boot and wiring, or through the silicone jacket. Connections should be made in parallel using an adapter. DO NOT pull on the wire to remove. Pull on the boot, or use a tool designed for this purpose.
When replacing plug wires, route the wires correctly and through the proper retainers. Failure to rotate the wires properly can lead to radio ignition noise and crossfiring of the plugs, or shorting of the leads t6 ground. Spark plug wire routings are shown in the specified vehicle information subsections which follow later in this section.
SPARK PLUGS
Resistor type, tapered seat spark plugs are used. No gasket is used on tapered seat plugs.
Normal service is usually a mixture of idling slow speed and high speed driving. Occasional high-speed driving is needed for good spark plug performance, because it gives increased combustion heat that burns away deposits of carbon or oxide that have built up from frequent idling or continual stop-and-go driving. Spark plugs are protected by an insulating nipple made of special heat-resistant material which covers the spark plug terminal and extends downward over a portion of the plug insulator. These nipples prevent flash-over, which causes missing, even though a dirt film is allowed to build upon the exposed portion of the plug.
Do not mistake corona discharge for flash-over or a shorted insulator. Corona is a 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.
IGNITION SWITCH
The mechanical key-controlled switch is located in the steering column on the right hand side just below the steering wheel. The electrical switching portion of the assembly is separate from the key and lock cylinder and is located on top of the column. Both work together through the action of the actuator rod.