Digital ignition timing

Back in the old days, tuning ignition timing was a matter of replacing weights and springs inside the distributor and by trial and error on the road assisted by a strobe light, determinng the optimum advacnce curve. When our dear Murena's came out, the there was specialised equipment available for mechanics to test the advance mechanism of distributors to ensure they were within specs. Today, of course, digital is the way forward and you can buy aftermarket distributors with bluetooth interfaces having replaced the weights. Tuning with these devices is best done on a rolling road. The potential is great!

But even in 1981, when the first 2.2 engines were fitted to the Murena with mechanical Bosch and Ducellier distributors, there were some electronic tools available, and these were in fact used on the Murena. We know, since the 2.2 was fitted with a crank sensor connected to the diagnostic connector. It was there for diagnostic purposes as the picture from my "Nachtrag der bedienungsanleitung" for the 2.2 shows. Note the "Geber für Zündzeitpunkteinstellung" and the "Diagnoseanschluss"!

I started wondering, a few years ago, about this sensor. How was it used? Noone I have talked to has seen a device that uses is. So was this just a meaningless item on a feature list? Perhaps! Yet, I kept thinking that it should be quite easy to get a signal from the crank sensor and compare the timing of it with the timing of the ignition signal, measuring RPM and advance.

Well, "Quite easy" turned out to be quite a project.

I have a fully working prototype now and will use this thread to document the way it works and how you can build one yourself. The picture is from when I was debugging my design in my lab. I will post pictures later of it working on my car and details about the design.