[Diy_efi] Ion Sensing project

[Ville Vartiovaara]

> I have a CDI system on my car, and will look it up tonight after work. Is
> this a feature that all CDI systems have? I don't remember anything with
> my system manual that says anything about arc-maintaining.

No, just some of them have. Capacitor discharge time is enough for most
systems, but the ones that need as long spark durations as coils offer
(lean mixture or otherwise difficult conditions) have one fitted. But as
all the patent papers talk about voltages between 100 and 400V never
exceeding the latter, I think that the ion sensing voltage limit is that
400V. Of course it depends on the spark plug gap adjustments, as the
limiting factor is the maximum electrical field strength allowed between
the electrodes, which is Volts/distance..
 
> Also have a question for you. What kind of ignition do you have on the
> engine you are doing this ion project with? Are you able to use the
> standard coils or something different?

It has just an old -82 type Ducellier distributor (worn ;) with
electronic breaker (not important) and a standard 3-wire coil. The coil
has two leads for primary, and the secondary is connected between the HV
plug and one of the primary leads. 

The only important thing for my ion sensing system is that the spark
voltage is positive, i.e. the primary leads are connected correctly,
because the feeding diode would otherwise be in conducting direction for
the spark going to the ion sensor! I tested it with a LED connected to the
secondary and poking the primary with a 1.5V flashlight battery (NOT 12V!
;) The LED lights only when the spark has correct polarity. 



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