Well, if your observations of cyl.8 are correct, you have determined the following: the coils themselves don't seem to be going bad; cylinder 8 is the problem; the plug wire for cyl 8 is not the problem.
Ok, so the possibilities are: a fault in the cap for #8, (carbon track,etc.) bad plug, plug gap too wide, ( forces the coil to develop higher voltage for that plug which either it cannot do, or the voltage developed is leaking off somewhere else since the plug is not firing. Example: say the bad plug needs 20kV to fire, the coil develops 18kV which is too much for the insulation on the wire, boot, or cap. The spark will jump or leak off at the weak point and never jump at the plug.
So the spark energy may be leasking off elsewhere, such as the boot to close to the head, etc.
Check those things, check the gap, temporarily replace the plug with another one, see if the problems stays or moves to another cylinder, you get the idea. Remember, the above is based on the assumption that your observations of #8 are valid.
Good hunting, Regards, George
Hey, on your idea of a bad lobe, what about a bad distributor gear, also? Could cause a bad dwell variation at one point in the rotation.....
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