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an ohm up to 40 million ohms, this makes
it very useful for testing the resistance in
most ignition system components.
If you suspect bad ignition wires, you can
test resistance of the wire while moving,
twisting and bending the wire. The
resistance values will typically be around
10KΩ per foot.
RED (+)
BLACK (+)
STARTER
MOTOR
ALTERNATOR OUTPUT
(BY-PASSED REGULATOR)
1
1
You can also check the resistance of the
ignition coil’s primary and secondary
windings, if you suspect a problem with
the ignition coil. You will need to do this
test, first, when the coil is hot, and again
when it is cold. You should also measure
from the coil’s case to each connector
and between the primary and secondary
windings should have a very low resistance,
typically from a few tenths of an ohm to
a few ohms and the secondary windings
have a much higher resistance typically in
the 10K ohm range.
To get the actual figures for a specific coil,
check the manufacturer’s specs.
WARNING: ALWAYS DISCONNECT
THE IGNITION COIL FROM THE IGNITION
SYSTEM BEFORE TESTING TO AVOID AN
ELECTRICAL SHOCK.
Spark Plug Wire (Secondary lgnition Wire)
Resistance Test
Spark plug wires should be checked if your
oscilloscope indicates that there may be a
problem or if they are more than two years
old. You should be careful when pulling
the spark plug boot from the insulator as
bonding may have occurred.
If you suspect a bad wire, test its resistance
while gently twisting and bending the
spark plug wire. If the resistance value
changes wile moving, twisting or bending
the wire and you are confident you have
a good connection, then replace the wire.
This test checks for high resistance or open
circuits in the secondary ignition wires
(spark plug wires).
To measure the wire resistance:
• Set the rotary switch to resistance (Ω).
Insert:
• Black lead in COM jack.
• Red lead in RPM,V, Ω jack.
Connect:
• The test probes to opposite ends of the
spark plug wire.
Typical measurements are approximately
10KΩ per foot of wire. For example, 2 feet
spark plug wire has about 20KΩ.
The measurement you make will be
dependent on the length of wire you
select.
Compare readings to other spark plug
Summary of Contents for UD226
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