Re: engin cut

[Dave Lawson <dlawson@digitalglobe.com>]

Colin,

>I have a problem with my ABT tuned UR quattro.
>In high gear, 4'th or 5'th and full trottel at low RPM (3500-4000), the
>engin cuts.If I dont push it to much, or if I shift to a lower gear the
>car runs OK.
>At high RPM there is no problem getting the boost up (1.25 bar).

What year ur-quattro? Could be a bad/intermittant air temp sensor
and the infamous 4000 rpm cutout. You should check the resistances, 
but the values depend on what year ur-q you have and what engine. 

Also what method is used to increase boost to 1.25 bar(18 psi)? The Abt
boost knob control or a stiffer wastegate spring? Has the car always had 
this problem or is it something new?

In the ECU PROM code there is a boost vs. RPM curve and for the stock
system the limit is at 0.9 bar boost pressure above 3500 rpm. I can't 
remember the exact point and don't have the plot handy. Below 3500,
it ramps up to 0.9 on a fairly steep incline. A few years ago when I had
a manual boost control knob in my ur-quattro and a good cold morning, I
could at full throttle, exceed the limit of this incline and the ECU would
cut power to the fuel pump. If you apply the throttle in a gradual fashion,
the fuel pump would never cut out.
  
HTH
-
Dave Lawson