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All 1976 certified engines in Motorhome and
TransMode vehicles are equipped with high
energy ignition systems .
GENERAL DESCRIPTION
The eight cylinder HEI distributor combines
all
ignition
components
in
one
unit.
The
ignition coil is in the distributor cap and
connects directly to the rotor . HEI performs
basically the same function as a conventional
ignition system, except the module and pick-up
coil of the HEI system do electronically what
the contact points of the conventional system
do mechanically.
The high energy ignition system is a pulse
triggered, transistor - controlled, inductive
discharge
ignition
system .
This
system
features a built - in ignition coil, an electronic
module and a magnetic pick-up assembly . This
assembly, located inside the distributor, con-
tains a permanent magnet, a pole piece with
internal teeth, and a pick-up coil . When the
teeth
of
the timer core
rotating on the
distributor shaft inside the pole piece approach
the . teeth 'of the pole piece, voltage is induced
in the pick-up coil . The electronic module then
turns the ignition coil primary current "on."
As the teeth align and then separate, a re-
versal in voltage potential signals the module
to open the ignition coil primary circuit. When
the primary circuit opens, a high voltage
induced in the ignition coil secondary winding
is directed through the rotor and high voltage
leads to fire the spark plugs. The capacitor in
the distributor is for noise suppression .
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 fuel mixtures.
IGNITION COIL
In the eight cylinder HEI system, the ignit-
ion coil is built into the distributor cap . The
coil is somewhat smaller physically than a
conventional coil, but has more primary and
secondary windings . It is built more like a true
transformer with the windings surrounded by
the laminated iron core. A conventional coil
has the iron core inside the windings .
Al-
though the HEI coil operates in basically the
same way as a conventional coil, it is more
effective in generating higher secondary volt-
age when the primary circuit is broken .
HIGH ENERGY IGNITION SYSTEM
ENGINE ELECTRICAL 6Y-7
ELECTRONIC MODULE
The electronic module is a solid state unit
containing five complete circuits which con-
trol
spark
triggering,
switching,
current
limiting, dwell control and distributor pick-up .
Dwell
angle
is controlled by
a transistor
circuit within the module and is varied in
direct relation to engine speed .
POLE PIECE AND PLATE ASSEMBLY
The pole piece and plate assembly (often
referred to as the pick-up coil assembly)
consists of the following :
1 . A stationary pole piece with internal
teeth.
2 . A pick-up coil and magnet which are
located between the pole piece and a bottom
plate .
CENTRIFUGAL AND VACUUM ADVANCE
The
centrifugal
and
vacuum
advance
mechanisms are basically the same types of
units
that
provide
spark
advance
in
the
breaker-type system . Centrifugal advance is
achieved through the rotation of the timer
core in
relation-- to
the
distributor
shaft .
Vacuum advance is achieved by attaching the
pick-up coil and pole piece to the vacuum
advance unit actuating arm.
THEORY OF OPERATION
The pick-up coil is connected to the elec-
tronic module, which in turn is connected to
the primary windings in the ignition coil . There
is a magnetic field surrounding the permanent
magnet and pick-up coil, which increases in
strength as
the
teeth of the
timer
core
approach alignment with the teeth
of
the pole
piece .
This increasing magnetic field induces a
voltage in the pick-up coil, and current then
flows to the ignition coil primary winding.
When the teeth are exactly aligned and start
to separate, the polarity of the pick-up coil
voltage is reversed .
It is this reversal of voltage potential which
signals the module to electronically shut off
the ignition coil primary circuit. This in turn
collapses the coil magnetic field and induces
high voltage in the ignition coil secondary,
firing one spark plug . A typical HEI schematic
and basic wiring diagram are shown in figures
2and3 .
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