General Technologies TD101 SmarTach + D: Gas and Diesel Tachometer with Ignition Voltage Tester - Manual (Page 9)

4. The end of the antenna is provided with a special sensor
which is designed to hook over spark-plug wires. This
sensor can be rotated on the antenna to more easily fit to
the wires. Hook this sensor on the spark-plug wire for
number one cylinder, as near a possible to the spark plug.
Pull gently on the antenna at right angles to the spark-plug
wire to seat the wire in the groove of the sensor.
5. Observe the IP (Ignition Peak) reading of the display.
Some jumping of the readings is normal and reflects actual
changes in the peak voltages of the ignition system.
6. Record or memorize the average reading. Repeat the test
for each of the spark-plug wires of the motor and note
any readings that are significantly higher or lower than
the average.
7 Ignition problems usually increase with motor speed and
may not show at idle speed. We recommend that the
spark analyzer test be made at increased motor RPMs,
equivalent to highway speeds, typically about 3,000
RPM.. Do not exceed maximum permissible (“red-line”)
motor speeds. Make all voltage test at about the same
motor speeds. Use the SmarTach+ tachometer function
to check the RPM.
Each reading is approximately equivalent to the peak voltage
present in the core of the spark-plug wire at the point you have
“hooked”. This reading is proportional to the kilovolts (KV)
required for the coil to initiate a spark across the plug gap, or
elsewhere in a defective system.
Diagnostic using the Ignition Peak readings
It is normal for readings on different spark wires to vary slightly
due to small variations in the contact area between the sen-
sor hook and thickness of insulation of the wire. The contact
position of the sensor on the spark wire can also cause some
variation, for example, if the sensor is put on the spark wire
nearer to the distributor or to the DIS coil, slightly higher volt-
ages readings will result.
Conversely, if the sensor is placed nearer to the spark plug on
the same wire, slightly lower voltage readings will result. This
is due to voltage drop along the wire caused by the resistance
of the wire. For diagnostic purposes, the attention should be
focused on SIGNIFICANT DIFFERENCES in readings caused
by problems in the engine or the ignition system itself. For ex-
ample, on a six cylinder engine, the following varying readings
would be considered as NORMAL because the differences are
NOT SIGNIFICANT.
CYLINDER #1 #2 #3 #4 #5 #6
READING 22.1 23.0 22.6 21.9 22.8 22.5
The above readings are quite close to each other, so no likely
problems are indicated. By contrast, the following varying
readings show ABNORMAL SIGNIFICANT DIFFERENCES in
cylinder #3 and #6.
CYLINDER #1 #2 #3 #4 #5 #6
READING 22.3 21.9 10.4 22.8 22.9 35.6
Except for cylinder #3 which is significantly LOW, and cylinder
#6 which is significantly HIGH, other cylinders are normal. Pos-
sible problems are to be suspected at cylinders #3 and #6.
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