GMC 1976 ZEO 6083 Maintenance Manual page 432

6Y- 52 ENGINE ELECTRICAL
3. Clean all serviceable plugs with an abrasive
type cleaner. File center electrode flat . Do not file
center electrode on new plugs.
4. Adjust spark plug gap to .080" using a round
feeler gauge.
5. Install plugs and torque to 25 ft . lbs.
DIAGNOSING HIGH ENERGY
IGNITION SYSTEM
(Using Voltmeter or Test Light, Ohmmeter, and
Module Tester J-24642) .
NOTE :
Careful adherence to the following proce-
dures will lead to the location and correction of
H.E .I . System problems . Normally, only a por-
tion of the procedures need be performed.
Engine Will Not Start :
1 . Insure that wiring connector is properly at-
tached to connector at side of distributor .
2 . Insure that all spark plug leads are properly
connected at distributor and spark plugs.
3. Connect voltmeter or test light from "BAT"
terminal lead on distributor to ground (figure 52).
4. Turn on ignition switch . If voltage is zero or
test light does not come on, repair open circuit be-
tween "BAT" terminal and battery.
5. When reading is battery voltage, or test light
lights, remove one spark plug lead by twisting spark
plug boot to loosen . Insert extension, hold spark plug
lead with insulating pliers so extension is 1/4 in .
away from dry area or engine block while cranking
engine, or install any good spark plug with .080 gap
in lead and lay on engine block while cranking en-
gine .
6. If sparking occurs trouble is not ignition dis-
tributor . Check fuel system and spark plugs. Check
timing . Distributor may have shifted.
7. If no spark, make Test No . 1 with Module
Tester J-24642 or equivalent as follows:
NOTE : Use Test No . 1 only in an engine no-start
situation.
a. Disconnect module harness connector
from the distributor cap (figure 55).
b. Connect J-24642 three-way connector to
the module harness connector.
Figure 55-Test No . 1 Using Tool J-24642
NOTE:
The three-way connector should connect
only one way to the harness connector. Match
wire colors between module harness connector
and tester three way connector.
c. Connect red lead of J-24642 tester to bat-
tery positive terminal and black lead to battery nega-
tive terminal .
d. Press and hold test button of J-24642 tester
while cranking engine .
NOTE :
During cranking, battery voltage must be
nine volts or more and engine speed 100 rpm or
more for tester to be accurate .
e. Momentary if red light and then green light
on Tester J-24642 comes on and stays on green.
Module and pickup coil are both good . If red light
stays on go to step 8 Test No . 2.
f. If pickup coil and module test good, remove
distributor cap and coil assembly by turning four
latches.
g. Check primary of ignition coil in cap for
continuity (step 1, figure 56). Reading should be zero
or near zero . If not, replace ignition coil .