94 F-150, 4.9L, EEC-IV engine control system. Misfire.
Visual Inspection.......Cap/rotor don't show any excessive burning. Coil had a burned secondary tower connector, half eaten away. Plugs had worn to .080 gap. Replaced coil, and plugs. Wires tested ok.
Misfire isolated to #3 cylinder. Least that's a starting point.
This is a distributor type ignition, with a Hall Effect sensor.
The complete lack of spark leads me to think the problem is in the primary. The GMM (similar to the KV Module on the older Snap On Vantage) shows intermittent 0 spark voltage. The scope also shows intermittent lack of secondary voltage (Any voltage!).
I'll get around to checking the primary waveform on the scope. I think I can trigger the scope on #1 cyl to observe a primary parade pattern. If the parade pattern is unstable, this will hopefully confirm that the sensor isn't being triggered by the windows properly. A fault inside the distributor, or related to the distributor.
I might note.......plug wires were switched to verify it isn't a bad wire, and the cap/rotor were switched to verify that the cap/rotor isn't the problem (old parts off my donor parts truck). I felt this completely eliminated any thought directed at the secondary.
So, now I'm at the fork in the road, and it seems to be leading inside the distributor