Distributorless Ignition: secondary vs primary voltage and current

The purpose of this test is to examine and compare the primary current and voltage vs the secondary voltage within a DIS unit.

How to perform the test

View connection guidance notes.

1. Ensure the ignition is turned off.
2. Connect a 10:1 attenuator to PicoScope Channel A.
3. Connect Channel A to the primary negative terminal of the coil unit.
4. Connect a secondary ignition pick up to PicoScope Channel B.
5. Connect the secondary ignition pick up around one of the coil HT leads and ensure the pick up has a good earth.
6. Connect a low amp clamp to PicoScope Channel C.
7. Select the 20 A scale and zero the clamp.
8. Connect the clamp around the coil unit primary power supply circuit.
9. Start the engine and run at idle.
10. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
11. Start the scope to see live data.
12. With your waveforms on screen stop the scope.
13. Turn off the engine. Ensure the ignition remains off.
14. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Note

If the secondary voltage waveform appears inverted then this is because the output is positive-fired. Move the secondary ignition pick up onto a different HT lead.

Alternatively, you can change the settings to look at a positive-fired coil by selecting the settings for channel B and changing the probe from Secondary Ignition Probe (Inverted) to Secondary Ignition Probe (Pos).​

Note

The orientation of the current clamp relative to the wire will determine whether it has a positive or negative output. If a live waveform does not appear on your screen, or appears to be inverted, try reversing the orientation of the clamp.

Note

This helpfile refers to a 10:1 attenuator. 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

These known good waveforms have the following characteristics:

• They are representative of standard primary voltage and current and secondary voltage waveforms.

Further guidance

GT394