Primary vs secondary ignition (10:1 attenuator, secondary pickup)

The purpose of this test is to monitor the relationship between the ignition's primary circuit and the secondary output for a distributor based ignition system.

Connection guidance

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from:

  1. Breakout leads.
  2. Back-pinning probes.

Testing sensors and actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control module.
  • When testing an actuator, it is desirable to gain access at the actuator

 

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.

How to perform the test

   

WARNING

Uninsulated HT pickups are designed to clip around double-insulated HT cables only – they are not designed for direct connection to a hazardous live voltage. To prevent injury or death, switch off the engine and secure against restart. Clean and inspect the HT lead for damage to insulation and fit only to undamaged fully insulated leads. Ensure that leads are safely clear of hot and / or rotating parts. The engine can now be restarted for the test duration.

  1. Connect a 10:1 attenuator to channel A of PicoScope.
  2. Connect channel A to the negative terminal on the ignition coil and to earth.
  3. Connect a secondary HT pick up lead to channel B of PicoScope and onto the ignition coil king lead. Ensure the pick up lead has a good earth.
  4. Start the engine and allow it to idle.
  5. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  6. Start the scope to see live data.
  7. With your live waveform on screen stop the scope to stop your capture.
  8. Stop the engine and turn off the ignition.
  9. Use the Waveform Buffer and Zoom tools to examine your waveform.

Waveform notes

The example waveform shows the exact relationship between the ignition's primary circuit and the secondary output. The primary circuit transfers its characteristics into the secondary through 'mutual inductance' and mirrors the primary exactly.

The blue trace shown in the example is the Low Tension (LT) signal, measured from the coil's negative terminal (marked number 1). The red trace is the High Tension (HT) output voltage measured at the king lead.

A permanent or intermittent loss of the secondary picture is usually due to a failing coil or HT (High Tension) voltage tracking to earth. Losing the primary picture will result in a total loss of HT voltage.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, Distributor ignition primary voltage or Distributor ignition secondary voltage 

Example ignition coil

Further guidance

Please see individual waveform topics:

  • Ignition secondary
  • Ignition primary (king lead)

GT389-1

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • Secondary ignition pickup (capacitive with BNC)

    £58.00

  • 10:1 Attenuator

    £64.00

  • Back-pinning Probe Set

    £40.00

  • Flexible Back-pinning Probe

    £3.00

  • Small Crocodile/Gator Clips

    £2.00

  • Large Dolphin/Gator Clips

    £10.00

Help us improve our tests

We know that our PicoScope users are clever and creative and we’d love to receive your ideas for improvement on this test. Click the Add comment button to leave your feedback.

Add comment

Your email address will not be published. Required fields are marked *

Guided test: Primary vs Secondary