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Ignition Analysis

The kV Module focuses on one distinctpart of the secondary ignition waveform,

the firing section.

The firing section consists of the firing lineand the spark line, also known as PowerkV and Spark kV. The duration of the sparkline is often called the burn time, and ismeasured in milliseconds.

Power kV

The firing line (power kV) is measured inkilovolts and represents the amount ofvoltage required to start a spark across thespark plug gap. Firing voltage mustovercome secondary circuit resistanceincluding secondary cables (if present),rotor gap(if present) and the spark plug.Remember that the spark plug air gap istypically the highest resistance in the circuit.

Here's some examples of ignitionpatterns on a Vantage histograph.

Note that the Power kV graph of all thecylinders should remain relatively stableat a steady engine speed.

By triggering on an individual cylinder wecan see that it is normal for firing voltage

to vary in any single cylinder.High spikes or kV readings indicate highsecondary circuit resistance. This canbe caused by a lean air/fuel mixture, awide spark plug gap, or a high resistanceor open spark plug wire. The highspikes above are caused by an open inonly one of the spark plug wires. Theother spark plug wires appear to be

good. Spark finding a high resistancepath to ground outside the cylinder (ignwire arcing to ground) could also createhigh firing voltage.

Power kV graph of all cylinders

Power kV graph of single cylinder

High spikes or kV readings

The firing section

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Low spikes or kV readings indicate lowsecondary circuit resistance. This can becaused by a rich A/F mixture, a narrowspark plug gap, low resistance or shortedspark plug wire, or low compression. Thelow spikes shown are caused by a short inonly one of the spark plugs. The otherspark plugs appear to be good. Sparkfinding a low resistance path to groundoutside the cylinder (ign wire shorted toground) could also create low firing voltage.

Spark kV

Spark kV represents the voltagerequired to maintain spark for theduration of the spark event.

Normal Spark kV should be between 1and 4 kV. High Spark kV readings indicatehigh secondary circuit resistance.

Low Spark kV readings indicate lowsecondary circuit resistance.

Burn Time

Burn time represents the duration of thespark event and should normallymeasure between 1 and 3 milliseconds.Burn Time is directly affected by FiringkV. If Firing kV increases, Burn Timedecreases. If Firing kV decreases BurnTime increases.

In a DIS or Waste Spark ignition systemit is important to remember that eachcylinder has a companion cylinder. Foreach pair of cylinders a single ignitioncoil fires both cylinders spark plugssimultaneously. Power kV is measuredon a cylinder when on the compressionstroke. Waste kV is measured on a

cylinder when on the exhaust stroke.The polarity of each pair is such thatone spark plug fires positively and theother one fires negatively. The voltagemeasurements will typically be slightlyhigher on the positively fired cylinders.

Low spikes or kV readings

Burn time

Low spark kV readings

Spark kV readings

Normal spark kV readings

DIS Power and Waste kV readings