Chapter
B
: Ignition System Diagnosis and Repair
44
There are several advantages of multiple ignition coil
systems. With coils serving only one or two spark plugs
there is much more dwell time available ensuring a hot-
ter spark than a single coil can provide. The location of
the coils reduces or eliminates the need for spark plug
wires and the maintenance they require. Finally, the
smaller coil operates at a lower temperature which adds
to its expected life. Regardless of the coil design, the di-
agnostic processes are very similar.
Ignition Coil Diagnosis
The resistance and current draw of the ignition coil can
be tested with an ohmmeter or an
ammeter
, respec-
tively. Test a coil at its normal operating temperature.
Resistance will change with temperature. Before testing,
make these preliminary checks:
1. Be sure the coil is securely mounted and all electri-
cal connections are clean and tight.
2. Check for a cracked or burned coil tower(s).
3. Check for a dented, cracked, or distorted housing.
Winding Resistance Test
Before attempting to measure the resistance of the pri-
mary and secondary windings, disconnect the battery
ground cable, primary wiring, and high-tension lead.
Use an ohmmeter to measure resistance as follows, fig-
ure 2-18:
1. Connect one ohmmeter lead to the positive (bat-
tery) primary terminal of the coil.
2. Connect the other ohmmeter lead to the negative
(distributor) primary terminal of the coil.
The ohmmeter will display primary winding resistance.
If reading is not within specifications, replace the coil. If
primary winding resistance is within range, check the
secondary resistance:
1. Connect one ohmmeter lead to a coil tower sec-
ondary terminal.
2. For coils serving one cylinder only, touch the sec-
ond ohmmeter lead to one of the coil primary ter-
minals and note the reading. For coil packs serving
a pair of cylinders, touch the other lead to the mat-
ing cylinders coil tower secondary terminal.
Current Draw Test
Several manufacturers provide current draw specifica-
tions for their ignition coils. Current draw is measured
with an ammeter. Test procedures vary; follow the Ser-
vice Manual recommendations. Some current draw
tests are performed on a running engine, others while
cranking the engine with the starter, or with the engine
stopped, ignition on, and primary circuit complete.
To test current draw, disconnect the positive (battery)
primary wire from the coil and connect it to the positive
lead of the ammeter. Connect the negative lead of the
VHz~
~
10A
RPM
+
COM
A
C F
RPM
V
%
OFF
VHz
Fig. 2-18.
Checking secondary coil winding resistance with an
ohmmeter.
VHz~
~
10A
RPM
+
COM
A
C F
RPM
V
%
OFF
VHz
DISTRIBUTOR
BATTERY
IGNITION
SWITCH
COIL
Fig. 2-19.
Checking ignition coil current draw with an ammeter.
Summary of Contents for ASE-A8
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