Ignition Coil Secondary
1972 Dodge Challenger · 440ci V8 Six Pack
Sensor Type
inductive
Waveform Type
ac-sine
Location
Center tower of distributor cap, fed from coil secondary high-tension terminal
Pins
1-pin connector
Idle Frequency
33.3 Hz
Timebase
5ms/div
Voltage Scale
5kV/div
Trigger
2kV, rising edge
Wiring
High-tension ignition wire (typically black or orange suppression core wire from coil to distributor cap center)
Expected Voltage Range
At Idle
0V to 15000V
At Higher RPM
0V to 25000V
Expected Pattern
Sharp firing spike to 8-15kV, followed by 1-2ms burn time at 2-4kV, then oscillating coil dissipation ringing
Known-Good Waveform
Firing line should spike sharply to 8-15kV depending on cylinder load and plug gap, followed by relatively flat burn voltage of 2-4kV for 1-2 milliseconds. After spark ends, expect 3-5 oscillations as coil energy dissipates. All eight cylinders should show similar firing voltages within 2-3kV of each other.
Common Failure Patterns
One or more cylinders show firing voltage above 18kV with short burn time
Cause: Excessive spark plug gap, worn plugs, bad plug wire, or distributor cap carbon tracking
Firing line drops below 5kV with extended burn time
Cause: Fouled spark plug, shorted plug wire, or incorrect plug heat range causing carbon buildup
Intermittent missing firing lines or extreme voltage spikes above 30kV
Cause: Deteriorated distributor cap/rotor, moisture in distributor, or failing coil insulation
Diagnostic Tips
Six Pack carburetion can cause rich conditions affecting center carb cylinders differently. Use capacitive pickup on plug wire; never pierce vintage suppression core wires.
Related Diagnostic Trouble Codes
P0300P0301P0302P0303
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.
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