Ignition Coil Secondary
1972 Dodge Challenger · 340ci V8
Sensor Type
inductive
Waveform Type
pulse-width
Location
Secondary high-tension tower on top of single coil, feeding distributor cap via coil wire
Pins
1-pin connector
Idle Frequency
33.3 Hz
Timebase
5ms/div
Voltage Scale
5kV/div
Trigger
2kV, rising edge
Wiring
High-tension ignition cable (typically black or dark color with metallic core suppression wire)
Expected Voltage Range
At Idle
0V to 35000V
At Higher RPM
0V to 40000V
Expected Pattern
Sharp initial firing spike of 8-15kV (higher with wider plug gaps or lean conditions), followed by spark duration burn line at 2-4kV for 1-2ms, then coil oscillation ringing at decreasing amplitude
Known-Good Waveform
Secondary waveform should display consistent firing spikes across all 8 cylinders between 8-15kV under normal conditions. Spark line (burn time) should be relatively horizontal at 2-4kV for 1.0-1.5ms duration. All cylinders should show uniform pattern; variations of more than 3kV between cylinders indicate problems. Coil oscillations after spark should show 3-5 diminishing waves.
Common Failure Patterns
Firing line exceeding 18kV or one cylinder significantly higher than others
Cause: Excessive spark plug gap, lean fuel condition on that cylinder, worn spark plug, high resistance in plug wire or distributor cap terminal
Short or absent spark line, immediate drop to zero after firing spike
Cause: Fouled spark plug, carbon tracking in distributor cap, shorted plug wire, plug gap too small
Low firing voltage below 5kV across all cylinders
Cause: Weak ignition coil, excessive rotor gap in distributor, low primary voltage due to ballast resistor failure
Irregular or split firing spikes, multiple firing events
Cause: Moisture or carbon tracking in distributor cap, cracked coil tower, deteriorated plug wires with corona discharge
Diagnostic Tips
Use capacitive pickup around coil wire or individual plug wires. Factory plug gap is 0.035 inches for points, 0.040-0.045 for electronic ignition. Inspect distributor cap for carbon tracking between terminals and check rotor phasing - these are extremely common failure points on high-mileage Mopar distributors.
Related Diagnostic Trouble Codes
P0300P0301P0302P0303
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.
Free, no signup. View all waveforms for this vehicle