What is wrong with these coils.

1998 F150 4.6L
So I took some waveforms of the ignition coils on this truck with a dead miss. Because I wasn’t confident in reading the scope I just swapped coils (I know I know...) and the miss followed the coil but I wanted to know what I could learn from these waveforms

The first one to me like good, the second one has a lot of hash and concerned me, the third one has a weird ramp after the spark, and the forth one was the one that wasn’t firing at all.


These were captures of the secondary ignition waveform.

The second one is classic failed Ford ignition coil. I'm not sure about the physics involved, but I've always associated that waveform with the spark 'ringing' in the coil instead of going across the plug. I have yet to see that particular waveform caused by a plug issue.

The third and fourth ones might be caused by the probe placement on the coil. I usually see the third one when the probe isn't on that sweet spot, and therefore the capture loses amplitude and detail. The fourth seems like more of the same. I'm really not trying to sweat you. I've just seen the same thing doing my own secondary testing.

Look at the included images

Cut the burn line in half, anything in the first half is outside of the cylinder, anything on the right is inside of the cylinder. Spark wasn’t making it into the cylinder...


The weird down Ramp is a failure in the insulation on the primary winding.

Thanks a bunch you guys! Probe placement could have certainly been the issue, as a couple were kinda hard to get to. It may or may not help that I was just using an alligator clip and not an actual probe :silly: . The shop did end up putting new plugs and coils in the truck, but unfortunately I was out of the shop that day and wasn't able to get after results or confirm the fix myself. Thanks again for the help.