DIY_EFI Digest V1 #259

[Jens Knickmeyer]

<Daniel Ridge> wrote:
> 
> > >What's Digifant?  
> > >
> > >RD
> > 
> > Just another vw fuel system that was for all intents and purposes was
> > propietary and short lived. I believe it was used on late 60's early
> > 70's squarebeeks. The name was repulsive enough to keep me from ever 
> > learning about it.
> 
> The Vanagon kept Digifant and four-speed transmissions and the leading
> edge of automotive technology for many years (snicker).
> 
> How could it not be a Bosch system, though? I know little about it, but it
> was my understanding that Digifant bridged the gap between LJet and
> Motronic (ie integrated spark but dumber brain)
> 
> What is it really?
> 
> -Dan

Digifant is, as you said, a bridge between LJet and Motronic and handles
ignition and injection. The injection system is the same as the Digijet
which is also called L2-Jet. It was the first LJet which used digital 
instead of analog design. The L3-Jet is nearly the same, except that
the ECU is mounted on the AFM. The Digifant's injection system is
a MPI, all injectors are batched.

Digifant includes an ignition which is based upon the Dignition. It
controls dwell and timing, the supercharged engines and some high
compression engines have a know sensor. The knock sensor's signal is
filtered by an analog filter circuitry and is measured only in a small
window after ignition (simply done by switching the filered signal to
the MCU by a CD4066).

The Digifant ECU is a "multi purpose" ECU, it can be used with a MAP or
a MAF sensor, with or without knock sensor. MAP is used on the supercharged
engines, MAF on the other ones (this goes for German VWs, situation might
be different in other countries). When the Digifant came out in the early
'80s, it used two MCUs, a 80xx and a 68HC05. Later, VW switched to one HC11 
instead of using two MCUs. Digifant has an OBD which got more sophisticated
over teh years of production. The first ECUs had a blink code output, later
a high speed diagnostic interface was used.

Digifant ECUs are produced by Bosch (small cases) and Siemens (large 
cases).

Jens ('92 VW Polo-G40)