Electronic spark timing ! PLEASE HELP !

[Walter Petermann]

Jose,
I don't know if this would help at all, but have you tried averaging 
your y counts? Now that you have a 40 tooth wheel you could take ten
y counts, maybe remove the highest and lowest values then average the
rest. 
Just for encouragement, the Jaguar XJ40 uses only 3 notches for the
timing or 120 degrees!

 Walter  (pushing the envelope over my head)

> Jose Carlos Rublescki wrote:
> 
...
> The problem comes with the ignition part. In my first system, the MCU
> received  from the engine one pulse each 90-degrees of engine rotation
> (on TDC's). For each 90 degree period the MCU counted the number of clock
> pulses (2 Mhz clock), let's say n, and then it did simple aritmethics as
> follows:
> 
> 90 DEGREES = n clock pulses
> x  DEGREES = y pulses.
> 
> So if I wanted a spark to appear x DEGREES after the 90-degree mark, I
> should just have to program the MCU to generate the spark after y clock
> pulses.
... 
> I should work fine in theory, but the problem I found is that there was
> sometimes too much variation from one 90-degree period to the next.
... 
> My BIG question is that there are here lots of cars made by Volkswagen
> where the ECU only reads one pulse each 90-degree of engine rotation. Do
> they just live with the fact that they will have spark timing variations
> or do they have some misterious way (at least to me) make this
> calculation?
> 
> After I gave up using the system above cited, I decided to use a 40-teeth
> wheel attached to the engine like FIAT and GM do here (only they have
> different teeth count). I now get much better results, but they're still
> not as great as I would expect. 
...