GMC 1976 ZEO 6083 Maintenance Manual page 426

6Y- 46 ENGINE ELECTRICAL
IGNITION TIMING
Idle Speed (R.P.M .) . . . ... . .... . . .. . . . ... . . ... . ... . . .. . . ... . ... . . . . . . . .. . . .... . . .. . . . ... . .... . . .. . . . ... . . . .. . . .. . . . .. . . ... . . 1100
Distributor Setting ... . . ... . . ... . . . . . . . . . . . .. . . . ... . . .. . . ... . ... . . .. . . . .. . . .... . ... . . . ... . .... . ... . . . ... . .... . ... . . ... . 8° BTDC
(*) With Distributor Vacuum Ports on Carburetor Plugged.
DISTRIBUTOR VACUUM CONTROL
Model No. . . . . ... . .... . ... . . . . . . . . . . . .... . . .. . . . .. . . ... . . ... . . ... . ... . ... . .... . ... . . . .. . . .... . . .. . . . ... . .... . . .. . . . ... . ... . .... . ..1973408
Inches of Mercury to Start Advance .. . ... . ... . . .. . . ... . . ... . . . . . . . ... . . ... . . . . . . . ... . .... . . .. . . . .. . . ... . . ... . ... . 8-10
Inches of Mercury for Maximum Advance . . ... . .... . ... . . . .. . . ... . . ... . . . .. . . .... . ... . . . .. . . ... . .... . 18 .5-20.5
Maximum Advance (Distributor Degrees)* .. . ... . . .. . . ... . . ... . . .. . . . ... . .... . . .. . . . ... . .... . . .. . . . .. . . .... . ... . ... . 12.5
(*) Plus or Minus one Degree .
IGNITION COIL
Model No . . . .. . . . .. . . ... . .... . . .. . . . ... . .... . . .. . . . .. . . ... . . .. . . .. . . ... . . ... . .... . ... . . . ... . . ... . . .. . . . . .. . .... . . .. . . . .. . . ..1115221
SPARK PLUGS
Make . ... . . ... . . .. . . . .. . . ... . . ... . . .. . . . .. . . . ... . ... . . . .. . . ... . . ... . ... . ... . . ... . .. .. . . .. . . . . . . . .... . ... . . . ... . .... . . .. . . . .. . . .... . ... . ... . .. AC
Type . ... . .... . . .. . . .. . . . .. . . . ... . ... . . ... . . ... . . ... . . ... . . .. . . . .. . . .. . . .. . . . .. . . ... . .... . ... . . . .. . . .... . . .. . . . ... . .... . . . . . . . .. . . ... . . .. R-45S
Size .. . . .. . . . .. . . .. . . . ... . .... . . .. . . . . . . . ... . .... . . .. . . . .. . . ... . . ... . .... ... . . ... . .... . ... . . . . . . . .... . ... . . . ... . .... . . .. . . . ... . .... . ... . .. 18MM
Point Gap . . . . . . . . .. . . ... . . ... . . .. . . . .. . . .... . . .. . . . .. . . ... . . ... . ... . ... . . ... . .... . ... . . . . . . . .... . . .. . . . .. . . .... . ... . . . .. . . ... . .... . ... . .040,
Torque (Ft. Lbs.) .. . . .... . ... . . . .. . . ... . . ... . . ... . . .. . . . .. . . .. . . .. . . . .. . . ... . .... . ... . . . .. . . .... . . .. . . . .. . . .... . ... . . . .. . . ... . . ... . ... . 35
Hex Size . .. . . ... . . ... . . ... . . .. . . . .. . . ... . .... . . . . . . . ... . .... . . .. . .... .... . ... . . ... . . .. . . . ... . .... . . .. . . . ... . .... . . .. . . . .. . . .... .... . ..13/16,
Distributor Clamp to Block Bolt (Ft. Lbs.) .. . . .. . . ... . .... . . .. . . . .. . . .... . . .. . . . .. . . .... . . .. . . . .. . . ... . . .. . . 12-17
HIGH ENERGY IGNITION SYSTEM
IMPORTANT:
Identify ignition system before ser-
vicing 1975 vehicles with 1974 certified engines
are equipped with standard breaker point igni-
tion systems. 1975 certified engines are equipped
with high energy ignition systems. To determine
year engine was certified, refer to decal on en-
gine valve cover.
GENERAL DESCRIPTION
(FIGURE 46)
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 operates basically in the same manner as
a conventional ignition system except the module
and pick-up coil of the HEI system replace the con-
tact points of the conventional system .
The High Energy Ignition is a pulse triggered,
transistor controlled, inductive discharge ignition
system . The magnetic pick-up assembly located in
side 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 teeth of the pole piece, an
induced voltage in the pick-up coil signals the all
electronic module to open 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 high voltage leads
to fire the spark plugs. The capacitor in the distribu-
tor is for radio noise suppression .
The module automatically controls the dwell
period, stretching it with increasing engine speed.
The HEI system also features a longer spark dura
tion, made possible by the higher amount of energy
stored in the coil primary. This is desirable for firing
lean and EGR diluted mixtures .
IGNITION COIL
In the 8 cylinder HEI system, the ignition 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 sur-
rounded by the laminated iron core. A conventional
coil has the iron core inside the windings . Although
the HEI coil operates in basically the same way as a
conventional coil, it is more effective in generating
higher secondary voltage when the primary circuit is
broken .