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Look for the burn line to be fairly clean without a lot of hash (“noise”). A lot of hash can indicate an ignition misfire in
the cylinder due to over-advanced ignition timing, bad injector, fouled spark plug, or other causes. Longer burn lines
(over 2
ms)
can indicate an abnormally rich mixture and shorter burn line (under 0.75 ms) can indica
t
e an
abnormally lean mixture.
Look for at least 2, preferably more than 3 oscillations after the burn line.
This indicates a good ignition coil (and a good condenser on point-type ignitions).
DI (Distributor Ignition) Secondary (Conventional Single and Parade)
Secondary ignition pat
t
erns
are very useful when diagnosing
igni
t
ion related malfunctions
.
The secondary scope
pattern is divided into three sections:
SECONDARY FIRING SECTION
The firing section consists of a firing line and a spark (or burn) line. The firing line is a vertical line that represents the
voltage required to overcome the gap of the spark plug. The spark line is a semi-horizontal line that represents the
voltage required to maintain current flow across the spark gap.
SECONDARY INTERMEDIATE SECTION
The intermediate section displays the remaining coil energy as it dissipates itself by oscillating between the primary
and secondary side of the coil (with the points open or transistor off).
SECONDARY DWELL SECTION
The dwell section represents coil saturation, which is the period of time the points are closed or the transistor is on.
The ignition (or distributor) dwell angle is the number of degrees of distributor rotation during which the points or
transistor are closed (or magnetic saturation time in degrees).
Normally, it takes about 10
to 15 ms for an ignition coil to develop complete magnetic saturation
f
rom primary current.
The secondary ignition test has been an effective driveability check for over three decades along with the primary
ignition test. The ignition secondary waveform can be useful in detection of problems in mechanical components of
engine and fuel system, as well as the ignition system components.
When the PARADE mode is selected, this instrument will present a parade of all the cylinders, starting at the left with
the spark line of the number 1 cylinder. The instrument will display the pattern for each cylinder’s ignition cycle in the
engine’s firing order. For example, if the firing order
f
or
a given engine is 1
,
4,3,2, the
instrument will display the
ignition cycles for each cylinder as shown starting with cylinder number 1, then 4, then 3, and then 2.
6-61
Firing Line (spark initiated)
Spark is extinguished
Spark Line (or Burn Line)
Dwell Section
Firing
Section
Intermediate Section
Coil oscillations
Points open or
transistor turns OFF
Points close or
transistor turns ON
4. locate fouled or damaged spark plugs that cause a cylinder misfire (from the burn line).
It’s sometimes advantageous to test the ignition primary when the ignition secondary is not easily accessible.
• Symptoms
No or hard starts, stalls, misfires, hesitation, poor fuel economy
• Test Procedure
1. Connect the CH A lead to the ignition coil primary signal (driven side) and its ground lead to the chassis GND.
2. With the Key On, Engine Running (KOER), use the throttle to accelerate and decelerate the engine or drive the
vehicle as needed to make the driveability problem or misfire occur.
3. For cranking test, set the Trigger mode to Normal.
4. Make sure that the amplitude, frequency, shape and pulse width are all consistent from cylinder to cylinder. Look
for abnormalities in the section of the waveform that corresponds to specific components.
•
Reference Waveform
VEHICLE INFORMATIONS
YEAR
:
1987
MAKE : Chrysler
MODEL : Fifth Avenue
ENGINE : 5.2 L
FUELSYS : Feedback Carburetor
PCM_PIN : CH A to Negative side of ignition coil
STATUS :
KOER (Key On Running)
RPM : Idle
ENG_TMP : Operating Temperature
VACUUM : 20 In. Hg
MILEAGE : 140241
• Troubleshooting Tips
Look
f
or
the drop in the
wave
f
orm where the ignition coil begins charging to stay
relatively consistent,
which
indicates consistent dwell and timing accuracy of individual cylinder.
Look for a relatively consistent height on the “arc-over” voltage or firing line. A line that is too high indicates high
resistance in the ignition secondary due to an open or bad spark plug wire or a large spark gap. A line that is too
short indicates lower (than normal) resistance in the ignition secondary due to fouled, cracked, or arcing spark plug
wire, etc.
Look for the spark or burn voltage to remain fairly consistent. This can be an indicator of air-fuel ratio in the cylinder.
If the mixture is too lean, the burn voltage may be higher, and if too rich, the voltage may be lower than normal.
6-60
The Ignition Peak voltage and Burn voltage measurements are available in this test,
but they should be corrected to account for the turns ratio of the coil windings.
Look closely to see that the pulse width (dwell) changes when engine load and RPM
changes.
MAX = 170 V
DUR = 2.07 ms
DWELL = 12.4 °
OF CYL 1
Ignition coil begins
charging here
coil oscillations
spark or burn
voltage
burn
line
arc-over or
ignition
voltage