Measure car engine speed RPM via the cigarette lighter

I setup my new oscilloscope to measure a car's engine speed by connecting to the cigarette lighter.  The inductive kicks from the ignition coil provide a timing signal that can be used to calculate RPM.  In this particular car (a DeLorean), the engine fires unevenly by design, so the inductive kicks are not all regularly spaced.
http://en.wikipedia.org/wiki/V6_engine

http://ranwhenparked.net/2010/09/14/what-lies-beneath-the-controversial-prv-engine-part-3/