[Diy_efi] Digifant

[Bernd Felsche]

On Fri, Jan 03, 2003 at 12:54:56AM +0800, Mike wrote:

Get some sleep, Mike! :-)

> As the car has had it from day one then its not worth pursuing
> unless it troubles you enough to get an aftermarket ECU. If it

I'm planning to build one - eventually. Not having much luck with
"hardware" right now so I'll keep that project shelved a little
longer.

> was my car from new or almost new it would very soon drive me
> to distraction, and you've put up with this for so long, yet
> its ironic your comment about 10 million not being a problem
> as its a design in feature ~`:o mmmm ?

The SAE papers published by VW at the time discuss the control
strategies - which appear to extract the maximum torque from
whatever fuel is in the system. At the same time, increasingly
strict emission requirements as well as the desire to minimise fuel
consumption (tending to operate on the lean side of stoich) pushed
the envelope so that the knock boundary would be nearby.

Working within the limits of cheap processors at the time, Digifant
will ping and/or reduce power output depending on not just the fuel
but also ambient conditions as the Octane Number Requirement (ONR)
of especially the (10:1 and greater) high-compression engines
varies. 

At low engine speeds, airflow is slow and any swirl/tumble that may
help to resuce detonation is also slow. I guess that the aggressive
mapping introduced by VW for low speeds was kept to allow the
benefits of high octane to be felt immediately; with audible pinging
being annoying but not destructive.

> Maybe it does need a suppression cap to ensure the knock sensor
> doesnt cause false readings by the ECU, ie. 'some' knock vs
> a 'bad knock signal, adding a suppressor cap in the right place
> may well be worth a try...

> Are you really sure its a feature of the car from new or almost
> new - have you ever swapped an ecu and 'bosch amp' and coil etc ?

ECU was swapped for a little test run; from a car without lambda
control but otherwise the same. Still pinged. So it's not just a
function of mixture control - ignition and mixture control were for
a long time distinctly separate (two micros; one Intel for ignition
and the other a Motorola for fuel) - only around 1990 were micros
sufficiently capable to merge the functions.

Volkswagen didn't indicate that the ignition side could influence
fuelling directly in any of their literature at the time; even
though temporary enrichment is one way of reducing or pinging at low
engine speeds.

-- 
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