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Christy,
That picture is of the voltage pattern of my ignition system. Check out those books I sent you (since some of the info I'm looking for is in there), and read about the primary and seconardy sides of the "conventional, breaker point ignition system".
You "read" the picture left to right over time, while up and down is voltage, lots and lots of voltage.
The basic idea (as I recall from ignition 101), is that the points close for a while, and during that time, a charge builds up in the windings of the coil. When the points open, WHAM, you get a spark. The picture, above, is what that spark looks like to a very fast volt meter (the oscilloscope).
The "correct" picture of a single spark shows a big spike (like this one) and several little ones, called ringing, right after it (like this one), BUT, I think there should be more little ones than this, AND I am not sure what to make of the extra bump in the middle. Lastly, the little tail before the big wham means something, but I forget what.
So, part of tuning your car is to have the "best" spark you can. And part of the job is making sure that the spark gets where it has to go at exactly the right time.
The quality of the spark is dependent on the health of your battery, the various primary wires (the stuff that carries 12 volts), coil, cap, balast(s), connectors, ignition module (if present), rotor, condensor (if present), points, plugs, engine ground and distributor.
The timing of the spark is dependent on the gap of the points (measured as dwell), position of the distributor relative to the motor, and the timing of the valves relative to the piston (ensured by your timing chain & cam shaft & valve clearance).
We went over your motor's spark timing and with the exception of that 4-5 degrees of timing chain stretch, your car's ignition timing is rather OK.
One sure-fire way to ensure a quality spark is to replace EVERYTHING with new components. That's what you did by getting new points, rotor, cap, wires, plugs (which you've cleaned a few times). Also, the tests to observe the voltage in the primary circuit confirmed that all was rather healthy. You replaced everything but the coil itself. Which MIGHT need to be replaced, but do you want to blow 100$ on a coil just because of a might?
The engine oscilloscope check I just did is how you can confirm a coil problem, and in fact most any problem with the ignition. All you need is this fancy scope. In my case, I just happen to have two of them. One seems to work (thus the picture), the other is very suspect. Tomorrow, I dig that other one out of the basement and try it on for size.
A while ago, there was an article in the star about building your own engine scope for under 100$ (thanks to a used component often available on ebay). If I bothered to pick up a small brass rod like I was supposed to this week, I'd have THREE scopes and would be trying that one out tomorrow too, but I never did get to that.
-CTH
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