91 200Q wastgate freq valve

[Phil@sievers.com (Phil Payne)]

In message <UPMAIL04.199610151639010437@msn.com> "Mike Miller" writes:

> The 91 200q (3B engine)does not have the feature of testing using the fuel
> pump relay as far as I know. The way the frequency valve works is the ECU
> pulses it to provide boost to the bottom of the WG to open it, thereby
> controlling/maintaining/limiting boost  - if the valve is open, or partially
> open, then boost is applied all the time to the bottom of the WG so you never
> reach full boost.

Interesting.  The 1988/9 ur-quattro uses a crossover valve - there are
thus _three_ pipes attached.  Normally, the chamber below the diaphragm
is fed directly from a bypass cast into the inlet manifold, providing
pre-throttle pressure to lift the wastegate against the spring.  This
is a pretty brute-force operation.  Additionally, the ECU can hook the
chamber _above_ the diapragm either to post-throttle manifold pressure
(to partly counteract the pressure in the chamber _below_ the diaphragm
and thus push the wastegate down) or to turbo inlet pressure - which
tends to lift the wastegate.

 Phil Payne

 (phil@sievers.com, despite what the bounces say.  If I don't
  reply, your message is probably still stuck on a Demon punt.)

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