GMC 1976 ZEO 6083 Maintenance Manual page 435

ENGINE ELECTRICAL 6Y- 5 5
Careful adherence to the following procedures will lead to the location and correction of HEI system problems . Normally
only a portion of the procedures need be performed.
A. ENGINE WILL NOT START. USE
I I
B. ENGINE RUNS ROUGH.
VOLTMETER OR TESTLIGHT.
A-1 .
A-3.
A-4 .
A-6.
1 . Insure that wiring connector is properly attached to connector at side of distributor.
2. Insure that all spark plug leads are properly connected at distributor and spark plugs.
Connect voltmeter from "BAT"
terminal lead on distributor to
ground .
A-2. Turn on ignition switch .
If voltage is zero, repair open
circuit between "BAT" termi-
nal and battery .
If reading is Battery voltage,
twist spark plug boot to loosen,
remove lead, insert extension,
hold spark plug lead with insu-
lating pliers so extension is 1
/4"
away from dry area of engine
block while cranking engine or
remove one spark plug lead .
Install any good spark
plug
with .080 gap in lead and lay
on engine block while crank-
ing engine .
A-5 . If sparking occurs trouble is
not ignition distributor.
Check fuel system and spark
plugs and secondary wiring .
Check timing (distributor
shifted) .
A-7. Proceed to Component Checks.
DIAGNOSING HIGH ENERGY IGNITION SYSTEM
WITHOUT USE OF MODULE TESTER J-24642
SYSTEM CHECKS
ON THE VEHICLE
B-1 . Insure that proper fuel is being
delivered to carburetor .
B-2. Check all hoses for leakage.
B-3. Visually inspect and listen for
sparks jumping to ground .
B-4. Check initial timing (distributor
shifted) .
B-5. Check centrifugal advance on
engine.
B-6. Twist boots to loosen, remove
all spark plugs and check for
usual defects - proper gap,
fouling, cracked insulators, in-
side and out, etc. Check sec-
ondary wiring .
B-7 . If no defects are found follow
procedure under Component
Checks .
C-11 . If no defects have been found,
remove connector and two at-
taching screws and replace
module .
C. COMPONENT CHECKS USING
OHMMETER .
C-1 . Remove cap and coil assembly
by turning four locking latches .
C-2. Inspect cap and coil assembly
and rotor for spark arc-over .
C-3.
C-4.
C-5.
Check primary coil . Connect
ohmmeter, Step 1, Figure 56 .
Use low scale. Reading should
be zero . If not, replace coil .
Check secondary of coil . Con-
nect ohmmeter, Step 2, Figure
44. Use high scale. Reading
should not be infinite .
If reading is infinite, check cap
and carbon button for arced or
burned condition. If necessary,
replace cap. If cap and rotor
button do not appear defective,
replace ignition coil.
C-6. Connect test stand vacuum
source to vacuum unit .
C-7. If vacuum unit is inoperative,
replace.
C-8. Check pick-up coil for broken
wire or open . Connect ohm-
meter, Step 1, Figure 59 . Use
middle scale. If ohmmeter
reads less than 500 ohms or
more than 1500 ohms (while
flexing leads) replace pick-up
coil . (C-10 below) .
C-9. If Step 1 is ok, check pick-up
coil for ground with ohmmeter,
Step 2, Figure 59 . Use high
scale. If reading is not infinite
(no deflection on meter) re-
place coil . (C-10 below) .
C-10 . Remove unit from engine, re-
move rotor and shaft assembly
from housing and remove thin
"C" washer to replace pick-up
coil (refer to distributor com-
ponent repair earlier in this
section) .
Diagnosing HEI