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91 200q owners - low boost
In message <9608191350.AA25035@orion.crd.ge.com> email@example.com (John Mallick) writes:
> Hmmm...now that I think about it, is the function of the grey hose and
> the wastegate frequency valve to provide backpressure on the diaphragm
> to keep the wastegate closed, or is it to provide front pressure to
> keep the wastegate open?
Both/either, depending on what the computer tells the valve to do. If you
accelerate hard uphill in third gear, you can feel a faint cycling effect on
the engine's power. That is this valve doing its stuff.
> The default position of the wastegate
> frequency valve is to provide turbo outlet pressure to the hose; when
> energized it doesn't.
No, but it doesn't matter. It can be tested in situ. This is the ur-quattro
MB and 20v sequence - I expect it will be the same on this engine:
a) Ignition off.
b) Spare fuse into socket on top of fuel pump relay.
c) Ignition on - do _NOT_ turn the engine with the starter.
d) After four seconds (German mechanics don't service RHD cars) remove fuse
from fuel pump relay.
The yellow engine warning light will blink 4433 in the usual groups. The
fuel pump relay will be driven by the computer, and the fuel pump will run.
e) Re-insert the fuse, and remove it after 4 seconds.
The engine light will blink 4441 and the control valve N7 will operate.
f) Remove the fuel pump fuse. (J13?)
f) Re-insert the spare fuse on top of the fuel pump relay, and remove it after
The engine light will blink 4442 and the boost limiter valve (the one you're
interested in) will be operated. The pipe that goes from the top of the valve
to the wastegate is supposed be connected in turn to the other pipe from the
top of the valve and the pipe that enters the bottom. Take the first pipe off
the wastegate, and remove the other two pipes from the valve body. With your
finger over one spigot at a time, you should feel perfect resistance and no
resistance alternately to a blow into the valve from the wastegate pipe. You
should also be able to feel the valve operating. Unlike the wastegate itself,
it _is_ important that this valve doesn't leak. Its function is to allow the
computer to fill the space above the wastegate diaphragm with either low
pressure air (from the turbo inlet) or high-pressure air (from the inlet
(If you do the fuse trick again, the computer will operate the cold start valve
for 10 seconds.)
If you want to repeat this sequence, do it by switching off the ignition,
replacing the fuel pump fuse, starting the engine, switching off and then
Committee Member, UK Audi [ur-]quattro Owners Club