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10-68
IGNITION SYSTEM
ELECTRICAL SYSTEMS
(344)
b. Testing Coil for Open and Grounded
Circuits
Before using a coil test instrument, the coil
should be tested for open and grounded cir-
cuits, using a 1l0-volt test lamp and test points.
1.
Apply test points to both primary ter-
minals of coil.
If
test lamp does not light, the
primary circuit is open.
2. Apply one test point to the high tension
terminal, and the other test point to one of the
primary terminals.
If
secondary circuit is not
open, the lamp will not light but tiny sparks
will appear at test points when they are rubbed
over terminals.
If
secondary circuit is open, no
sparks will occur.
3. Apply one test point to a clean spot on
the metal coil case and touch the other point
to the primary and high tension terminals,
If
the lamp lights, or tiny sparks appear at the
points of contact, the coil windings are grounded.
4. A coil with open or grounded windings
must be replaced since internal repairs cannot
be made.
It
is unnecessary to test such a coil
with instruments.
If
windings are not open or
grounded, a test for short circuits and other in-
ternal defects should be made with a reliable
coil test instrument.
c. Coil Test Instruments
Two general types of instruments are used
in testing ignition coils. One type makes use of
an open or protected spark gap, while the other
reports the condition of the coil on a
meter.
The spark gap type of tester should always be
used comparatively, that is, the questionable
coil should be compared with a coil of same
model that is known to be good. Both coils
must be at the same temperature and identical
test leads must be used. Certain variables
caused by altitude, atmospheric or spark gap
electrode
conditions are usually present in the
spark gap type of test.
The meter type testers are usually designed
to permit testing the coil without making any
connection to the secondary terminal. This
eliminates the variables usually present in the
spark type of test and avoids the necessity for
comparison with a good coil.
Since different makes and models of coil
testers differ in their methods of use, as well as
in the markings on meters, the instructions of
the manufacturer must be carefully followed
when using any coil
teste?'.
The instrument
must be frequently checked to make certain
that
it is accurately
calibrated.
Regardless of instrument or method used,
the coil must be tested at normal operating tem-
perature because internal defects often fail to
show up on a cold test.
10-50
DISTRIBUTOR
CONDENSER
TESTS
When a condenser is suspected of being
faulty it should be tested with a reliable con-
denser tester to determine whether it is actually
the cause of ignition trouble. The condenser
should be tested for (a) high series resistance
(b) insufficient or excessive capacity (c) low
insulation resistance.
A special condenser tester is required to make
these tests. When using a condenser tester the
instructions of the manufacturer must be care-
fully followed. IMPORTANT: The condenser
must be at normal operating temperature when
it is being tested.
a. Hi
gh
Se r ie s
Resistance
High series resistance in the condenser circuit
causes condenser to be slow in taking the charge
and, consequently, a higher than normal volt-
age is developed across the contact points when
they first start to open
.
This higher voltage
causes more disturbance at the contact points,
which in turn causes more rapid wear and more
tendency toward oxidized surfaces. The condi
-
tion can become severe enough to cause com-
plete failure of the ignition system.
It
would
first show up during starting and low speed
operation.
High series resistance may be caused by in-
ternal resistance in condenser or by resistance
in the connections. Any defect caused by inter-
nal resistance should show up at low mileage
since this does not change very much with time
or use. The damaging changes are in the
connections, in which looseness, corrosion, or
broken strands may develop.
New condensers may have a series
resistance
as low as .05 ohm. Some condenser testers are
set to reject condensers which have a resistance
of .3 ohm; however, tests show that the resist-
ance can go to .5 ohm before ignition perform-
ance is affected.
b.
Insuffici ent
or Excessive Capacity
The condenser specified for use in the Buick
ignition system has a capacity of .18 to .23
microfarads.
If
a
conde
nser
is used which does not have
the specified
capaci ty
of
.18 t
o .23
microfarads,
oJ
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