GMC 1976 ZEO 6083 Maintenance Manual page 427

C-TERMINAL
CONNECT TACHOMETER
FROM THIS TERMINAL
TO GROUND.
(SOME TACHOMETERS
MUST CONNECT FROM
THIS TERMINAL TO
ENERGIZER POSITIVE (+) .
CONSULT TACHOMETER
MANUFACTURER.)
GROUND
TERMINAL
B+ TERMINAL
BAT. TERMINAL
(CONNECTED TO
IGNITION SWITCH)
A4000
Figure 46-Typical High Energy Ignition
ELECTRONIC MODULE
The electronic module is a solid state unit con-
taining five complete circuits which control 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 fol-
lowing :
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 mech-
anisms 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-
ENGINE ELECTRICAL 6Y- 4 7
up coil and pole piece to the vacuum advance unit
actuating arm .
THEORY OF OPERATION
The pick-up coil is connected to transistors in the
electronic module. The electronic module is con-
nected to the primary windings in the coil . As the
distributor shaft turns the timer core teeth out of
alignment with the teeth of the pole piece a voltage
is created in the magnetic field of the pick-up coil .
The pick-up coil sends this voltage signal to the
electronic module, which determines from RPM
when to start current building in the primary wind-
ings of the ignition coil .
Each time the timer core teeth align with the pole
piece teeth the pick-up coil magnetic field is changed
creating a different voltage. The pick-up coil sends
this different voltage signal to the electronic module
which electronically shuts off the ignition coil pri-
mary circuit. This in turn collapses the coil magnetic
field, induces high secondary voltage and fires one
spark plug . A typical HEI schematic and basic wir-
ing diagram are shown in Figures 47 and 48 .
The electronic module delivers full battery volt-
age to the ignition coil which is limited to five to six
amperes. There is no primary resistance wire in the
HEI system . The electronic module triggers the clos-
ing and opening of the primary circuit instantane-
ously with no energy lost due to breaker point arcing
or capacitor charging time lag. The capacitor in the
HEI unit functions only as a radio noise suppressor .
The instantaneous and efficient circuit triggering
enables the HEI system to deliver up to approxi-
mately 35,000 volts through the secondary wiring to
the spark plugs.
An exploded view of the HEI system is shown in
Figure 49 .
Figure 47-HEI Schematic