I was certainly under the impression that the capacitor in the ignition of
older cars was there to form an LC circuit that would oscillate and make the
spark both stronger and longer lasting.
I was not always aware of that because I had heard rumors that the primary
function of the capacitor was to make the points last longer. I am now
quite certain this is not true. If it were true, the car ought to run with
the capacitor removed. I know first hand these cars will not run without
the capacitor.
During my grad school days I had two Fiats. (Don't ask why.) In order to
keep those cars running, and not pay all my money to a mechanic, I became a
"Saturday morning mechanic." I set the timing and adjusted the points every
two months or even every month. My wife got stranded once because the
capacitor failed. We had the car towed to a garage and the mechanic fixed
it by replacing the capacitor. He said the capacitor was "open." I
remarked my surprise that the car would not run with an open capacitor. He
told me "of course it won't run because the capacitor and coil form an LC
oscillator." In order to confirm this, the next time I tuned up the cars I
removed the capacitor to see what would happen. Sure enough, the engine
would not run without the capacitor.
An aside... I never bothered to learn how "electronic ignition" works
because I never had any trouble with one. Some people didn't have many
problems with the old points/capacitor systems because they had regular
service, and because they had V8 engines that could tolerate a bit of
ignition problems and still run. On the other hand, in the early 1970s a
lot of us were responding to the energy shortage by buying cars with small
4-cylinder engines. If these were not kept in tip-top shape they ran very
poorly and maybe wouldn't start in the winter. Although there were many
areas that could cause problems, the points and timing were certainly areas
that demanded considerable attention. I sure considered it a blessing when
I bought my first "electronic ignition" car. I don't care if I never touch
the distributor/points/condenser again.
Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817