Ignition Coil Secondary
1972 Dodge Challenger · 360ci V8
Sensor Type
inductive
Waveform Type
pulse-width
Location
Center tower of distributor cap, secondary winding output from coil mounted on intake manifold
Pins
1-pin connector
Idle Frequency
25 Hz
Timebase
5ms/div
Voltage Scale
5kV/div
Trigger
2kV, rising edge
Wiring
High tension wire (typically orange/red carbon core wire) from coil tower to distributor cap center
Expected Voltage Range
At Idle
0V to 25000V
At Higher RPM
0V to 35000V
Expected Pattern
Sharp spike to 8-15kV firing voltage, followed by burn line at 1.5-3kV for 1-2ms, then coil oscillations and return to baseline
Known-Good Waveform
Secondary should display sharp firing spike of 8000-15000V with clean rise time under 10 microseconds, followed by horizontal burn line at 1500-3000V lasting 1-2 milliseconds. Coil oscillations after burn should dampen quickly within 3-4 cycles. All 8 cylinders should show consistent firing voltages within 3kV of each other.
Common Failure Patterns
Firing voltage exceeds 20kV, extended spark line duration, intermittent misfires
Cause: Excessive secondary resistance from worn spark plugs, wide plug gaps, deteriorated plug wires, or corroded distributor cap terminals
One cylinder shows significantly higher firing voltage (5kV+ difference)
Cause: Open or high resistance spark plug wire, cracked distributor cap, worn distributor rotor, or fouled spark plug on that cylinder
Short or absent burn line, immediate drop after firing spike
Cause: Shorted spark plug, carbon tracking in distributor cap or rotor, or grounded secondary wire
Excessive coil oscillations (ringing) after burn line
Cause: Open or missing suppression resistor in distributor rotor, damaged coil windings, or poor connections
Diagnostic Tips
Use capacitive pickup on #1 spark plug wire or inductive clamp. Distributor cap and rotor are common failure points on this era - check for carbon tracking, cracks, and brass terminal erosion. Mopar electronic ignition conversions are common on these vehicles.
Related Diagnostic Trouble Codes
P0300P0301P0302P0303
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.
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