Ignition Coil Secondary
2021 Ford F-150 · 3.5L V6 EcoBoost
Sensor Type
inductive
Waveform Type
ac-sine
Location
Secondary output integrated into coil-on-plug assemblies, direct connection to spark plug
Pins
Unknown
Idle Frequency
25 Hz
Timebase
5ms/div
Voltage Scale
5kV/div
Trigger
Capacitive pickup, 10kV threshold
Wiring
Internal coil winding, no external wires (capacitive pickup required for testing)
Expected Voltage Range
At Idle
-5000V to 35000V
At Higher RPM
-8000V to 40000V
Expected Pattern
Initial firing spike 15-25kV, burn time 1.0-1.5ms with stable burn voltage 3-5kV, followed by coil oscillations
Known-Good Waveform
Firing line should reach 15-25kV under light load with sharp vertical rise, followed by horizontal burn line at 3-5kV for 1.0-1.5ms duration. After burn, coil oscillations should show 3-6 dampened waves. All six cylinders should show similar patterns with firing voltage within 3kV of each other under same load conditions.
Common Failure Patterns
Firing line exceeds 30kV with shortened burn time below 0.8ms
Cause: Excessive spark plug gap wear, lean mixture, or increased cylinder compression from carbon buildup
Inconsistent or absent firing line, intermittent sparks visible in waveform
Cause: Coil internal breakdown, carbon tracking in coil boot, or moisture intrusion
Diagnostic Tips
Use capacitive pickup on coil body or spark plug wire boot connection. EcoBoost direct injection creates higher combustion pressures requiring higher firing voltages than port injection engines. Compare turbo boost conditions between cylinders as uneven boost distribution affects firing requirements.
Related Diagnostic Trouble Codes
P0300P0301P0302P0303
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.
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