Ignition Primary Circuit Resistance Test - Cadillac 54-6219 1954 Shop Manual

11-18
ENGINE ELECTRICAL
.035". The gap should be checked only with a round
wire gage, and should be adjusted by bending the
side electrode only. Never bend the center elec
trode. The plugs should be tightened in the engines
to 20-25 ft. lbs. torque.
The type 46-5 spark plug is used as original
equipment on all 1954 Cadillacs to satisfy the
majority of owners who largely drive at lower
speeds on shorter runs. For owners who drive at
higher speeds on longer runs, the cooler 44-5
type
plug is recommended, When replacing spark plugs,
note the condition of the electrodes. If they appear
to be excessively burned or blistered,a cooler plug
should be used. If the plugs have sooty carbon de
posits, a hotter plug should be used. Under no cir
cumstances, however, should a type 48 plug be used
in a 1954 engine.
31
Ignition Primary Circuit
Resistance Test
Excessive voltage drop in the primary circuit
will lessen the secondary output of ignition coil,
resulting in bard starting and poor performance.
1, Turn the voltmeter selector switch of the
Volts-Ampere Tester to the 4 volt position.
2. Connect test
leads as shown in Fig. 11-21.
3, Remove distributor cap and close breaker
points by rotating engine a fraction of a revolution
at a time with the cranking motor.
4. Be sure all lights and accessories are turned
off,
5, Turn ignition switch "ON". Voltmeter should
read not more than .1 volt.
6. Test ignition switch by turning it off and on
several times. Voltmeter should read the same each
time switch is turned on.
7. Test alt wires for tightness. Move them
about and note any change in meter reading.
8. Remove voltmeter
leads andplace themacross
the primary wire from the coil to the distributor
as shown by dotted leads in Fig. 11-21. Voltmeter
should read less than .1 volt.
NOTE: If voltmeter reading exceeds the spe
cified maximum, isolate the point of high resis
tance by placing the test leads across each con
nection and wire in turn, The reading across a
connection should be zero. The reading across
any one wire should be proportionate to its length
as compared to the length and allowable voltage
drop of the entire circuit.
32
Ignition Coil Tests
The coil in the ignition circuit of an engine acts
as a transformer by stepping up the battery voltage
to a voltage sufficiently high to jump the rotor gap
in the distributor and the spark plug gap while un
der compression. The common causes of coil failure
are as follows:
1, High resistance due to corroded connections
or broken wires.
2. Short circuits or breakdown of insulation be
tween turns of the coils and grounds.
3. Breakdown of insulation between the windings
and the core or case.
a. Reading the Coil Tester Meter
The OHM scale is to be used fnr measuring the
resistance from zero Ohms to 100,000 Ohms.
ro measure the resistance of a unit, connect
the positive primary and the ground lead clips
together. Turn the switch to the "DWELL-OHM"
position.
Adjust the Dwell-Ohm Regulator until the meter
reads on the set line. Disconnect the leads, Con
nect the unit in which resistance is being measured,
in series with the test leads. The meter will then
indicate the amount of resistance in the unit.
The "OHMS" scale is read from right to left
from 0 to 100,000 Ohms. FromO to the first gradua
tion indicates 100 Dhins. SC indicates 500 Ohms,
IM indicates 1,000 Ohms, lOOM indicates 100,000
Ohms,
b. Calibrating the Coil Tester
To assure an accurate test of the ignition coil,
Fig. 11-21 Ignition Primary Circuit Resistance Test