GMC 1976 ZEO 6083 Maintenance Manual page 428

6Y- 4 8 ENGINE ELECTRICAL
Distributor
Secondary
Wire
(To Spark
Plug)
Figure 48-HEI Basic Wiring Diagram
SERVICE OPERATIONS
ROUTINE MAINTENANCE
The HEI system is designed to be free from rou-
tine maintenance. No periodic lubrication is re-
quired . Engine oil lubricates the lower bushing and
an oil-filled reservoir provides lubrication for the up-
per bushing. There is no dwell adjustment as this is
controlled by the module . Timing can be set in the
same manner as the standard distributor. For proper
operation, however, it is necessary to keep ignition
wires and distributor clean and free of any corrosion.
If component part replacement should become
necessary, several items specific to the HEI system
should be noted .
Electronic Module
The electronic module is serviced by complete
replacement only . When replacing the module a lib-
eral coating of special silicone grease MUST be ap
plied to the metal mounting surface on which the
module will be installed. If this grease is not applied
the module will not cool properly which can cause
the module to malfunction. A tube of this special
silicone grease is supplied with each replacement
module . Make certain the replacement module is the
correct part number .
CAUTION : When connecting battery, as in
jump starting, reversing connections or
polarity, can result in damage to the elec-
tronic module.
Pole Piece and Plate Assembly
The pole piece and plate assembly (often referred
to as the pick-up coil assembly) is also serviced by
complete replacement only . Make certain the re-
placement assembly is the correct part number . The
pole piece and plate assembly should not be unneces-
sarily disassembled as the polarity of the assembly
could be changed and effect proper operation of the
vehicle.
Spark Plug Wires (Figure 50)
Because of the higher voltage, the HEI system
has larger diameter (8 millimeter) spark plug wires
with silicone insulation . The silicone wire is gray in
color, more heat resistant than standard black wire
and less vulnerable to deterioration. Silicone insult-
aion is soft, however, and must not be mishandled .
The spark plug wire boots seal more tightly to the
spark plugs . Twist the boot about a half turn in either
direction to break the seal before pulling on the boot
to remove the wire .
The spark plug cable retainer is designed to hold
the wires firmly to prevent chafing or cutting. The
wires cannot be repositioned until the cable retainer
is unlocked . To unlock the cable retainer use a small
screwdriver between the tub and the lock .
To remove wiring harness from cap, release wir-
ing harness latch and remove wiring harness both
right and left side (figure 51).
The eight spark plug wires and holder are re-
placeable only as an assembly . However, if it is neces-
sary to remove an individual wire from the wiring
harness assembly, hold grommet of wire down and
press retainer tub out of wire holder . To reinstall,
lightly lubricate tub end of spark plug wire with
silicone . Rotate wire until seated in holder .
WARNING : DO NOT REMOVE SPARK PLUG
WIRES WITH THE ENGINE RUNNING . THE
HIGHER SECONDARY VOLTAGE IS CAPABLE
OF JUMPING AN ARC OF GREATER DISTANCE
AND COULD CAUSE AN ELECTRIC SHOCK. OP-
ERATING THE ENGINE WITH ONE OR MORE
SPARK PLUG WIRES DISCONNECTED CAN
ALSO RESULT IN DAMAGE TO THE DISTRIBU-
TOR CAP .
Resistance specifications for both 7mm wires
used with standard systems and 8mm wires used
with HEI systems are identical (3,000 to 5,000 ohms
per foot). Inspect all spark plug wires for high resist-
ance and continuity with an ohmmeter. Ohmmeter
should be set on high scale. Connect ohmmeter leads
to the terminals at each end of the cable being tested .