My guess is under the distributor cap... worn rotor/cap, points.
it CAN also be, its VERY rare, but happened twice to me in the 60`s...rotor can be sitting at a so perfectly wrong place that there`s no contact...if its a manual car ,put it in gear ,give it a push so the rotor moves...if not manual, just take the cap off ,wiggle it a bit...
this happened on our Simca Vedette and on a friends Jaguar...not sure if it CAN happen on a GM car, but think it can...