Distributorless Ignition System primary ignition voltage

The purpose of this test is to examine the characteristics of the primary ignition waveform from within the DIS unit.

How to perform the test

View connection guidance notes.

1. Use manufacturer data to identify the coil circuit functions.
2. Ensure the ignition is turned off.
3. Connect a 10:1 attenuator to PicoScope Channel A.
4. Connect Channel A to the DIS coil pack primary negative terminal.
5. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
6. Start the engine and allow it to idle.
7. Start the scope to see live data.
8. With your waveform on screen stop the scope.
9. Turn off the engine and ensure the ignition is off.
10. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Note

If you are using a 20:1 attenuator please adjust the Probe settings for the relevant channel. These settings can be found under the Channel Options button, then: Probe > 20:1 Attenuator.

Example waveform

Waveform notes

This known good example shows a typical primary waveform.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, DIS / wasted spark ignition primary voltage

Further guidance

The ignition primary waveform is measuring the negative side of the ignition coil. The earth path of the coil can produce over 350 volts.

Within the primary picture there are several sections that need closer examination. In the waveform shown, the horizontal voltage line at the centre of the oscilloscope begins fairly constant at about 40 volts, but then drops sharply into what is referred to as the coil oscillation. 

There is no current in the coil's primary circuit until the dwell period which is when the coil is earthed and the measured voltage drops to zero. The dwell period is controlled by the ignition amplifier, and the length of the dwell is determined by the time it takes to build up the requisite 5-10 amps (depending on system). When this predetermined current has been reached, the amplifier stops increasing the primary current and maintains it until the earth is removed from the coil, at the precise moment of ignition.

The vertical line at the centre of the trace, called the 'induced voltage', is above 200 volts. The induced voltage is produced by a process called magnetic induction. At the point of ignition, the coil's earth circuit is removed and the magnetic field or flux collapses across the coil's windings. This in turn induces an average voltage between 150 to 350 volts. The coil's High Tension (HT) output is proportional to the induced voltage. The height of the induced voltage is sometimes referred to as the primary peak volts.

GT396