K-jetronic.......sucks.....

[Bernd Felsche]

Buchholz, Steven tapped away at the keyboard with:
> ... actually, if you are talking about my response, it was not the
> early golfs ... those had the stock K-jet if memory serves ... it
> was when VW went to its proprietary Digifant system rather than
> switching directly to Motronic.  I have yet to look up the part
> myself, but it is my understanding that the injector insert for
> the digifant equipped cars fits the same heads that the old CIS
> injector inserts did, but it allows a pulsed injector to be
> fitted.  

The Digifant injection hardware is derived from L-Jetronic.
Injector seats are interchangeable; the K-Jet shrouded injectors
have additional air passages.

The AFM potentiometer calibration may be different from L-Jet to
read air-flow "directly"; i.e. linear instead of the curve one would
get from from a simple vane-angle resolution. (It's pretty rough;
the one I've measured by rotating the vane actually had a "dip" in
the output.) i.e. the AFMs aren't generally interchangeable.

> I am not at all familiar with the VW line to know which models in
> what years were offered with the Digifant system, but I would
> imagine it would have been in the early 1990s ... 

Mid to late '80s. And still current (though much more "Motronic"
now). The early Digifant appeared around 1986, successor to the
Digijet. Digifant II became the most wide-spread, incorporated in
VW's and Audis until the early 1990's. Mine actually says "Motronic"
on the box, as well as Digifant.

Subsequent Digifant units were adapted to use throttle-position and
later thin-film air sensors.

Within each generation, the internals in the "box" became more
integrated. There are a couple of SAE papers on the subject. Early
Digifant units used two CPUs, one to perform ignition control, the
other fuel injection. That was basically the partial integration of
the Bosch knock-sensing ignition module and Digijet.

The "final" Digifant was 68HC11-based, with everything running on
the microcontroller.

The main short-comings of the Digifant system are air-flow metering
(vane-type meter, effectively wide-open at about 4000 rpm an the ECU
reverting to speed-density) and low-speed stability - due largely to
the absence of a suitable signal for crank/cam position. Up until
1990, most also lacked any OBD - other than the proprietary protocol
with supercharged engines (which, btw used MAP).

Digifant's main advantage as far a Volkswagen was concerned was
cost. Bosch was heavily involved in Digifant development.

-- 
Bernd Felsche - Innovative Reckoning
Perth, Western Australia
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