This module focuses on ignition coil primary current analysis and what it can — and cannot — tell you during diagnosis.

Tom covers the two main coil charging strategies (excess dwell and ramp-and-fire), how coupled inductors behave differently from simple RL circuits, and why the basic inductance formula doesn't directly apply to ignition coils.

A key takeaway is the limitation of current ramp diagnostics: a defective coil with little or no secondary output can produce a perfectly normal-looking primary current ramp. Real case study waveforms are used to demonstrate this, including side-by-side comparisons of good and bad coils that are nearly indistinguishable on even a high-resolution 12-bit scope.

The module establishes what actually matters when validating primary drive:

• Did the current reach an adequate level?
• Did the current cut off quickly enough?

If both conditions are met and secondary output is still poor, the coil is the problem — no ramp shape analysis required.