Ignition Coil Secondary
1972 Dodge Challenger · 383ci V8
Sensor Type
inductive
Waveform Type
ac-sine
Location
Center tower of single coil on firewall/intake manifold, distributes to spark plugs via distributor rotor and cap
Pins
1-pin connector
Idle Frequency
25 Hz
Timebase
5ms/div
Voltage Scale
5kV/div
Trigger
2kV, rising edge
Wiring
High-tension wire (thick insulated cable) from coil center tower to distributor cap center
Expected Voltage Range
At Idle
0V to 15000V
At Higher RPM
0V to 18000V
Expected Pattern
Firing spike 8-15kV, burn time 1-2ms at 2-4kV with oscillations, followed by coil oscillations at 30-40kHz
Known-Good Waveform
Secondary pattern shows initial firing spike of 8-15kV depending on cylinder load and plug gap, followed by 1.5-2.0ms burn time at relatively constant 2-4kV spark line. After burn, coil oscillations should show 3-5 clean dampening waves. All eight cylinders should show consistent firing voltage within 3kV of each other, with slight variations normal based on compression and mixture.
Common Failure Patterns
Firing voltage exceeds 18kV or shows extremely short burn time under 0.8ms
Cause: Excessive spark plug gap (over 0.035"), fouled plugs, open secondary wire, or high resistance in rotor/cap carbon button
One or more cylinders show firing spike below 5kV with extended irregular burn
Cause: Fouled or carbon-tracked spark plug, cracked distributor cap, or shorted plug wire
Intermittent missing cylinders or erratic firing patterns across multiple cylinders
Cause: Worn distributor cap terminals, excessive rotor tip erosion, corroded cap/rotor contact, or cracked coil tower
Diagnostic Tips
Use capacitive pickup or inductive clamp on plug wire. Parade pattern shows all eight cylinders sequentially - look for outliers. Distributor cap/rotor condition critical on this system; corrosion and carbon tracking common failure points after 30k miles.
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