Ignition Coil Inspection
Measuring arcing distance
The most accurate test for determining the condition of
the ignition coil is made by measuring arcing distance using
the coil tester for the 3-needle method.
Remove the ignition coil.
Connect the ignition coil (with the spark plug cap left in-
stalled on the spark plug lead) [A] to the tester [B], and
measure the arcing distance.
To avoid extremely high voltage shocks, do not
touch the coil or lead.
If the distance reading is less than the specified value, the
ignition coil or spark plug cap is defective.
3 Needle Arcing Distance
To determine which part is defective, measure the arcing
distance again with the spark plug cap removed from the
ignition coil lead.
If the arcing distance is subnormal as before, the trouble
is with the ignition coil itself. If the arcing distance is now
normal, the trouble is with the spark plug cap.
Measuring Coil Resistance
If the arcing tester is not available, the coil can be
checked for a broken or badly shorted winding with an
ohmmeter. However, an ohmmeter cannot detect layer
shorts and shorts resulting from insulation breakdown
under high voltage.
Remove the ignition coil (see Ignition Coil Removal).
Measure the primary winding resistance [A].
Connect an ohmmeter between the coil terminals.
Set the meter to the x 1 Ω range, and read the meter.
Measure the secondary winding resistance [B].
Pull the spark plug cap off the lead.
Connect an ohmmeter between the high tension lead and
the ground lead terminal.
Set the meter to the x 1 kΩ range, and read the meter.
Ignition Coil Winding Resistance
If the meter does not read as specified, replace the coil.
If the meter reads as specified, the ignition coil windings
are probably good. However, if the ignition system still
does not perform as it should after all other components
have been checked, test replace the coil with one known
to be good.
Check the high tension lead for visible damage.
If the high tension lead is damaged, replace the ignition
Spark Plug Cleaning and Inspection
Refer to the Spark Plug Cleaning and Inspection in the
Periodic Maintenance chapter.
7 mm (0.26 in.) or more
0.28 ∼ 0.38 Ω (at 20°C (68°F))
7.65 ∼ 10.35 kΩ (at 20°C (68°F))
ELECTRICAL SYSTEM 16-15