GMC 1982 Light Duty Truck, Руководство по обслуживанию

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ENGINE ELECTRICAL 6D -31
IGNITION SYSTEM - CONVENTIONAL ENGINES
GENERAL DESCRIPTION
CONTENTS
General Description.............................................. 6D-31
H.E.I. Distributor............................................... 6D-31
Ignition Timing.................................................. 6D-32
Secondary Wiring............................................... 6D-32
Spark Plugs........................................................ 6D-32
Ignition Switch................................................... 6D-34
Diagnosis.............................................................. 6D-34
H.E.I. Distributor............................................... 6D-34
On-Vehicle Service............................................... 6D-38
H.E.I. Distributor............................................... 6D-38
Remove and Replace......................................... .6D-38
Distributor.......................................................6D-38
Module............. ............................................. .6D-39
Pick-up Coil.................................................... .6D-39
Rotor...............................................................6D-39
Vacuum Advance Unit......................................6D-39
Integral Ignition Coil...................................... .6D-39
Capacitor.........................................................6D-39
Set Ignition Timing................................................6D-39
Spark Plug Wires................................................. .6D-39
Unit Repair.......................................................... .6D-40
GENERAL DESCRIPTION
The ignition circuit consists of the battery, the
distributor, the ignition switch, the spark plugs, and the
primary and secondary wiring. Refer to the Battery portion
of this section for battery information.
H .E .I. DISTRIBUTOR
The High Energy Ignition distributor used on all
engines combines all ignition components in one unit (Fig.
6D-13D and 6D-14D). The external electrical connections
are the ignition switch feed wire, the tachometer pickup, and
the six or eight spark plug leads. The ignition switch feed
connector to the distributor has full battery voltage when
the ignition switch is in the "R U N " and "START"
positions. There is NO RESISTOR WIRE FROM THE
IGNITION SWITCH TO THE DISTRIBUTOR. The
ignition coil is in the distributor cap and connects through a
resistance brush to the rotor. The High Energy Ignition
System is basically identical in operation to conventional
ignition except the module and pick-up coil replace the
contact points.
The High Energy Ignition is a magnetic pulse
triggered, transistor controlled, inductive discharge ignition
system. The magnetic pick-up assembly located inside the
distributor contains a permanent magnet, a pole piece with
internal teeth, and a 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 supression.
The magnetic pick-up assembly is mounted over the
main bearing on the distributor housing, and is made to
rotate by the vacuum control unit, thus providing vacuum
advance. The timer core is made to rotate about the shaft by
conventional advance weights, thus providing centrifugal
advance.
The module automatically controls the dwell period,
stretching it with increasing engine speed. The HEI system
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.
Electronic Spark Control
An additional electronic control (ESC) is used on
vehicles equipped with an LE9 engine. The Electronic Spark
Control (ESC) system is a closed loop system that controls
engine detonation by adjusting spark timing. The amount of
retard is a function of the degree of detonation.
there are two basic ocmponents in this system as
outlined below.
Controller. (Fig. 6D-15D)
The (ESC) controller processes the sensor signal and
applies it 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/amplifier which operates from 6 to 16 volts.
The controller has no memory storage.
Sensor (Fig. 6D-15D)
The (ESC) sensor is a magnetorestrictive device,
mounted in the engine block that detects the presence (or
abscence) 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.
ESC Vacuum Switch See (Fig. 6D-16D)
On LE9 engine equipped vehicles with automatic
transmission a "tip in" vacuum switch is used. Its function
is to provide a momentary contact closure (signal) to the
ESC controller during a throttle "tip in" condition which
then briefly retards spark timing to minimize knock.
The switch contacts are normally open under steady
engine vacuum conditions including no vacuum, and all
brief increasing vacuum conditions. Basically the switch
closes only during rapidly decreasing vacuum conditions
such as that encountered on rapid throttle operation.
When making compression checks, disconnect ignition
switch connector (pink wire) from HEI system.
No periodic lubrication is required. Engine oil
lubricates the lower bushing and an oil-filled reservoir
provides lubrication for the upper bushing.