Date:         Sun, 19 Nov 2000 13:28:43 -0800
Reply-To:     Dave Bayer <daveb@CP.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dave Bayer <daveb@CP.NET>
Subject:      Re: Knock Sensor Kit for A 86-91 Vanagon
Content-Type: text/plain; charset=us-ascii

> The knock sensor kits are designed for CIS based VWs like the Rabbit and
> Scirocco.  These cars had a very simple ignition system.  The hall sender
> style distributor was attached to a little black box in the rain tray and
> this controlled the firing of the coil.  The timing was changed via vacuum
> and centrifugal advancing.  The knock sensor kit replaces the distributor
> with a pure electronic one and a computer controls the timing.

        The knock ecu also happens to take manifold pressure iirc.
That is something that the digifant system does not use. Another
thing to consider is that the knock control unit is actually the
iginition control unit. It is mapping the advance of the spark.
Putting that signal inline with the digifant unit _most likely_
will end up advancing the spark too far to too little.

>  Another potential problem is the trigger wheel shutter
> openings.  On the 8V A2 series VWs there are two types of distributors... a
> xxx xxx 205 and an xxx xxx 205 S - both are electrically the same but you
> need the 205 S to work with the knock sensor computer as the trigger wheel
> on the 205 has smaller openings.  Again not a really big issue, as we could
> swap parts but it could cause some grief.

        The only way to really know how this is all going to
work short of either just plugging the thing in or looking
at the code embedded in those maps, is to take a dual input
oscilliscope or some other dual signal analyzer and time the
difference between the Hall sender and the resulting spark
in both the digifant and knock control systems. Then figure
out when the input signals are being generated in reference to
TDC and then do the math to figure out if swapping distributors
and the like is really going to work.

        That excludes the fact that you cannot mount the
knock sensor directly to the casting that containing the
cylinders as in the inline 4 engines and that aluminium
probably has different resonence characteristics than cast
iron.

        Basicly, I don't think the knock control unit is
going to work. Digifant II would be a closer approximation,
and iirc has nearly the same pin out as the digifant I ecu.
However, the digifant II unit was used on an inline 4 engine
with 10.0 compression verse the 9.x used in the waterboxer
and you still need to figure out what to do with the knock
sensor itself to make it reliable. Much research on the topic
will be necessary I would guess.

        Why not just strip the nice digifant system and move
to something like the aftermarket FI systems that gene berg
sells for Type Is.

dave