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PART
9-1-
GENERAL IGNITION SYSTEM SERVICE
9-3
ground through the closed breaker
points.
When the breaker points
open, the magnetic field built up in
the primary windings of the coil
moves through the secondary wind-
ings of the coil producing high volt-
age current. High voltage current is
produced each time the breaker
points open. The high voltage flows
through the coil high tension lead to
the distributor cap where the rotor
distributes it to one of the spark plug
terminals in the distributor
cap.
This
process is repeated for every power
stroke of the engine.
IGNITION SYSTEM TESTS-
CONVENTIONAL TEST
EQUIPMENT
TROUBLE ISOLATION
Ignition system troubles are caused
by a failure in the primary and/ or
the secondary circuit or incorrect ig-
nition timing. If an engine trouble
has been traced to the ignition system
from the "Engine Trouble Diagnosis
Guide," the trouble can be found by
performing an ignition system test on
a scope or by further isolating the
trouble to the primary or secondary
circuit as follows:
1. Disconnect
the
brown wire
from the starter relay I terminal and
the red and blue wire from the start-
er relay S terminal.
2. Remove the coil high tension
lead from the distributor
cap.
3. Turn on the ignition switch.
4. While holding the high tension
lead approximately
3
/t_
a inch from the
FIG. 2 -Battery to Coil and
Starting Ignition Circuit Test
FIG.
3 -Ignition Switch Test
cylinder head or any other good
ground, crank the engine by using an
auxiliary starter switch between the
starter relay battery and S terminals.
If the spark is good, the trouble
lies in the secondary circuit.
If there is no spark or a weak
spark, the trouble is in the primary
circuit, coil to distributor high ten-
sion lead, or the coil.
Primary Circuit
A breakdown or energy loss in the
primary circuit can be caused by:
1. Defective primary wiring, or
loose or corroded terminals.
FIG. 4 -Resistance Wire Test
2. Burned, shorted, sticking or im-
properly adjusted breaker
points.
3. A defective coil.
4. A defective condenser.
To isolate a trouble in the primary
circuit, proceed as follows:
Turn the ignition switch off and
remove the auxiliary starter switch
from the starter
relay.
Install the coil high tension lead in
the distributor cap, the red and blue
wire on the starter relay S terminal
and the brown wire on the starter
re-
lay I terminal.
Now perform a primary circuit
test.
Secondary Circuit
A breakdown or energy loss in the
secondary circuit can be caused by:
1. Fouled or improperly adjusted
sparlr plugs.
l. Defective high tension
wiring.
3. High tension leakage across the
coil, distributor cap or rotor result-
ing from an accumulation of dirt.
To isolate a trouble in the second-
ary circuit, proceed as follows
:
Turn the ignition switch off and
remove the auxiliary starter switch
from the starter relay.
Install the coil high tension lead in
the distributor cap, the red and blue
wire on the starter relay S terminal
and the l,rown wire on the starter re-
lay I terminal.
Now perform a secondary circuit
test.
PRIMARY CIRCUIT TESTS
A complete test of the primary cir-
FIG. 5-Coil to Ground Test
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