Why one output terminal of my car ignition coil gives less sparks than the other terminal. In fact, the 2 terminals are control by a single primary circuit of the same ignition coil!!! The other ignition coil has the same issue.

I have checked for all resistance readings of the PRIMARY AND SECONDARY CIRCUITS of each IGNITION COILS which shows normal values. No cracks, etc etc at all.

Please kindly help. Thanks.enter image description hereenter image description here

  • What is the year/make/model/engine in question? From the sound of it, you have a two headed coil, where one coil provides spark to two different cylinders. These are commonly called "wasted spark ignition systems". If so, one side is designed to put out less spark than the other, depending on what side is firing. – Pᴀᴜʟsᴛᴇʀ2 Nov 24 '19 at 16:24
  • Its Hyundai i20 1.2 2011 model. It has 2 ignition packs and each coil packs have 2 output terminals to fire 2 cylinders respectively. – Thang Tons Nov 25 '19 at 0:54
  • In other words, it's not an issue. This is the way it is designed to be. This is the way it runs. See this Wiki article. – Pᴀᴜʟsᴛᴇʀ2 Nov 25 '19 at 1:37
  • I've never seen a wasted spark system that fires stronger on the cylinder that's firing, so I don't think @Pᴀᴜʟsᴛᴇʀ2♦ is correct here. However it would be helpful to know how it is being tested. i.e. with plugs outside of cylinder? grounded how? etc. – David Holdeman Nov 25 '19 at 17:55
  • @DavidHoldeman - That's how wasted spark systems work. – Pᴀᴜʟsᴛᴇʀ2 Nov 25 '19 at 21:31

The internal insulation of the coil may be degrading.

To test the integrity of the insulation a Fluke meter with the ability to measure Conductance is needed. Set the meter to conductance and measure from a spark plug wire tower to the electrical plug. In a good coil, the meter will show a number that fluctuates. A bad coil, the meter will show "OL". Check both coil pairs to the electrical connector.

In this type of ignition, the primary and secondary windings of the coil should never interact. When the meter reads "OL" this means that there is some minor interaction because the resistance is low enough.


If you’re testing with a realistic setup of ignition leads and spark plugs then you should see similar sparks on both plugs. If you’re testing under different conditions then it’s quite possible that one side will arc before the other and draw most of the energy from the coil. So if you’re testing under realistic conditions then you likely have a problem, otherwise it may just be to do with the setup when you’re testing.

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