That's a very broad question that would take a book to answer. There
some decent write-on the subject you can find on the web.

2009/10/31, Mark Dearing <VWBrain@aol.com>:
> In a message dated 10/31/2009 11:09:48 A.M. Eastern Daylight Time,
> crescentbeachguitar@GMAIL.COM writes:
>
> Digifant.   1.9 is DigiJet
>
>
>
> hey guys other than the ingnition control system what is the difference
> between the two??   I have a 85 vannie running a 1.8L jetta motor with  the
> vannie controls system , only differnce I see is the jetta has a knock
> sensor
> that I just didn't use.  later  mark  d
>

--
Chris S.
Disclaimer: "Death and serious injury may occur"