I'm having fun with my Hantek 1008C and tried it out on my ignition system today. My 98 Mazda 626 GF 2L uses a coil pack waste spark system with each coil firing two plugs simultaneously.

I took a short one minute video and captured a few individual wave forms. Going over that video in slow motion I saw quite a variety of waveform shapes, however the fire lines were all about 2 milliseconds which is supposedly pretty good and close to the maximum possible. I don't think the scope was displaying every single spark event because I had the trigger set fairly high, however these two basic waveforms were the most common:

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This seems pretty normal, but I was wondering why that second spike was so high?

This is the other common one, and I'm assuming this is the waste spark?

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  • it could be noise (it looks pretty clean and it'd be better to compare against a parade pattern), but generally that shows a lean burn. What are the max voltage specs on your scope? You might want to use an attenuator in the future on stuff like primary/secondary and other high voltage captures like fuel injectors. – Ben Oct 15 '17 at 19:31
  • Found a relevant post: scannerdanner.com/forum/diagnostic-tools-and-techniques/… – Robert S. Barnes Oct 15 '17 at 21:29
  • @Ben Based on this page I'm pretty sure that's just the waste spark I'm looking at: autoserviceprofessional.com/article/92689/… – Robert S. Barnes Oct 15 '17 at 22:17
  • probably, you could do a parade pattern on the secondary and use a trigger on cyl 1 injector confirm. – Ben Oct 15 '17 at 22:29
  • @Ben I found the answer, the waste spark is superimposed on the power spark. So they're both normal sparks, the second just has a very low firing voltage of about 1.5kV. – Robert S. Barnes Oct 16 '17 at 14:16

OK, so I was reading this article from Motor magazine and those are apparently both normal sparks, and in a waste spark system, the waste spark is superimposed on the firing spark and can be seen as the thick spot on the firing line:

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The coil oscillations being so high and wild at the end could seem to indicate allot of leftover energy being wrung out of the coil on that first spark, or intermittent high resistance according to the above article. I'm not sure how it could have intermittent high resistance, but I did notice when looking through the video in slow-mo that on many of the sparks the waste spark firing line was almost to the top of the power spark firing line.

Regarding the low firing line on the second waveform, I found this article from Snap-On which says:

Low spikes or kV readings indicate low secondary circuit resistance. This can be caused by a rich A/F mixture, a narrow spark plug gap, low resistance or shorted spark plug wire, or low compression. The low spikes shown are caused by a short in only one of the spark plugs. The other spark plugs appear to be good. Spark finding a low resistance path to ground outside the cylinder (ign wire shorted to ground) could also create low firing voltage.

Some more info I found:

A fouled plug (or shored ignition cable), on the other hand, will show an unusually low firing voltage. ... A cylinder that shows an abnormally low firing voltage probably has a grounded spark plug (deposits bridging the electrode gap), or a shorted ignition cable. ... A longer than normal spark (1.8 milliseconds or more) is an indication that the firing voltage is experiencing little resistance because a plug is fouled or grounded (or a plug wire is shorted) probably due to accumulated carbon deposits. Fouling can be a problem if a plug's heat range is too cold for the application (which can be solved by installing hotter plugs). But it may also be the result of excessive oil consumption due to worn valve guides or seals, worn rings, or even short trip stop-and-go driving.

I have a fairly new coil, and I'm using the narrow tip NGK G-Power platinum plugs, so I'm theorizing maybe that could account for my low voltage sparks. They even claim their plugs reduce the required spark voltage. Maybe this is proof? My inclination is that there aren't any misfires since I don't have any symptoms. Gas mileage is great, there's no hesitation and my fuel trims are perfect.

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