Multi-coil-on-plug secondary ignition (positive-fired)

The purpose of this test is to examine a positive fired secondary ignition waveform from a Multi-Coil-on-Plug ignition unit.

 

WARNING

Uninsulated HT pickups are designed to clip around double-insulated HT leads only – they are not designed for direct connection to a hazardous live voltage.

To prevent injury or death, when connecting or disconnecting an HT pickup:

  1. switch off the ignition
  2. clean the HT leads
  3. inspect them for damage
  4. clip the HT pickup over the desired undamaged HT lead
  5. ensure all test leads are kept clear of hot or rotating parts before starting the engine

 

How to perform the test

View connection guidance notes.

  1. Ensure the ignition is switched off.
  2. Remove the multi-coil pack and insert HT extension leads.
  3. Connect HT pick-up lead between an extension lead and PicoScope Channel A. Ensure the HT pick-up lead has a good earth.
  4. Check all connections are secure, start the engine and allow it to idle.
  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 scope to see live data.
  7. With your waveform on screen stop the scope.
  8. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Note 

Many multi-coil ignition systems employ wasted spark coils, this means there will be both negative and positive fired spark plugs. If your waveform is missing or appears to be inverted you have two options;

  • Stop the test and move the HT pick-up lead onto a different cylinder
  • Stop the test and select the guided test from the automotive drop-down menu for a negative fired plug.

Example waveform

Waveform notes

The example waveform shows a typical picture from an engine fitted with electronic ignition. The waveform is from the coil-on-plug unit fitted on the Vectra Z22SE engine.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, COP (Coil on plug ignition) secondary voltage

Further guidance

The operation of the coil-on-plug unit is essentially the same as any other ignition system.

The distributorless ignition systems are fitted only to vehicles that have an even number of cylinders such as 2, 4, 6 or 8. This is because two cylinders are connected to one coil that produces a spark in both cylinders at the same time. This is commonly known as a wasted spark system. The two spark plugs are arranged so that one is fired on the power stroke of the engine and the other on the exhaust stroke of the opposing cylinder, offset by 360 degrees. After a complete rotation of the engine, the two cylinders are now on the opposing strokes and the two spark plugs fire again but with opposite roles to before.

On a 4-cylinder engine, there are two coils with individual drivers that tend to operate cylinders 1 and 4, and 2 and 3. This means there is a dual spark every 180 degrees, with one of those sparks wasted on an exhaust stroke of the opposing cylinder which is firing on the power stroke.

The only real difference between COP and other ignition systems is that each COP coil is mounted directly onto the spark plug, so the voltage goes directly to the plug electrodes without having to pass through a distributor or plug leads. This direct connection method delivers the strongest spark possible and improves the durability of the ignition system.

GT186

Disclaimer

Suitable accessories

  • HT Extension Lead

    £41.00

  • HT Extension Lead (set of 4 leads)

    £159.00

  • Secondary ignition pickup (capacitive with BNC)

    £58.00

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Guided test: Secondary (Positive-fired)