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Secondary Ignition (Plug kV)

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Secondary Ignition (Plug kV) Waveform Notes

The plug firing voltage is the voltage required to jump and bridge the gap at the plug’s electrode. Commonly known as the ‘Plug Kv’ (Kilo Volts).

The plug Kv’s will be increased by:

  • Large plug gaps
  • A large rotor air gap
  • A break in a plug lead
  • A break in the king lead
  • Worn spark plugs
  • A lean mixture
  • Rotor to reluctor misalignment

The plug Kv’s will be decreased by:

  • Small plug gaps
  • Low compression
  • Rich mixture
  • Incorrect ignition timing
  • Tracking to earth
  • Fouled plugs

A high resistance in the High Tension (HT) lead or the coil lead will not alter the plug Kv (however an increase in sparkline Kv will be evident). An open circuit lead will increase both the plug Kv and the sparkline Kv.

Use different voltage ranges for different tests:

  • 0 to 25 Kv for plug firing voltages and HT insulation testing.
  • 0 to 50 Kv for plug firing voltages on Distributorless Ignition System (DIS) and coil output testing.