Timmerman "Shrapnnel-Knobben" mod et. al.

urquattro urquattro at phoenixdsl.com
Wed Oct 18 08:23:31 EDT 2000

> This is great info.  Taking the leap into territory that I am only a bit
> familiar with has anyone done or looked into wiring a potentiometer in
> place of the resistor so that you could adjust the timing/fuel pump shut
> off point as the situation requires....
> Any thoughts or BTDT?
> >>To keep the fuel pump cutout from kicking in, you need to modify the
> >either by chip, or some less elegant way, eg. the resistor mod.  A 475
> >resistor is placed between pins 1 and 10 on the ECU pressure transducer,
> >which fakes the ECU into getting the value for a lower pressure.  this 1)
> >make the fuel pump shutoff at a much higher point, somewhere around 2.7
> >and will advance timeing across the board.  I have modified mine so I can
> >set the value a bit higher as the timing with 475 ohm tends to be a
> >to much advance, especially on a hot day under load.  A fixed value
> >to 600 ohm may be a better bet.
> >
... Paul's mod to the ECU was a resistor/zener mod, not simply a resistor.
The zener clamps the input to the A/D so that the ECU never thinks it sees a
pressure above that point and thus does not activate the overboost shutdown
mechanism.  Many people swear by this mod, claiming many miles of trouble
free service, but personally I would not recommend doing it.  As long as all
is well it may be fine, but be sure to keep all of the car in tip top shape
at all times, because if you get something like a tear in the WG diaphragm
things may change in a hurry.

I would also like to speak against the thought of putting some sort of an
adjustable voltage divider in the boost signal to the A/D on the ECU.  The
whole reason the ECU is there is to take inputs on manifold pressure, engine
RPM and throttle position and determine the operating parameters of the
engine ... ignition timing, WGFV position, and yes if the fuel pump should
be shut off.  By scaling the voltage you are causing the ECU to think that
the engine is running at a different point in the maps than it really is.
This may not be that bad a thing, but it is not likely that the timing
parameters will be better at this operating point than they would have been
if the engine really knew where it was operating.  Realize that I don't have
a problem with scaling the voltage out of the pressure transducer to
increase the active range available to the ECU, but if it is done, the code
in the ECU should have a commensurate change so that it "understands" the
new calibration.

To anyone who wants to gain an understanding of what is going on inside the
ECU I heartily recommend checking out Robert Houk's site:


While his work is focused on the ECU of the urquattro, most all of the
subsequent 10v turbos have a control system that is very similar ...

Steve Buchholz
San Jose, CA (USA)

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