boost instability

[Phil Rose]

At 7:30 AM +0200 5/18/03, Richard Tanimura wrote:
>
>To be perfectly honest, I have never really looked for the BPV on my car. If
>you find it, clue me.

Rich,
No diligent '91 200q owner can long remain ignorant of the BPV and/or
its location. :-) Perhaps you know the BPV by its _other_ name, which
is "throttle overrun" valve?

As to the valve's location: Assuming you know where the waste gate
frequency valve is located--find the WGFV's electrical connector, and
then look directly below it--barely 1 cm down--and you'll see a
large, cylindrical lump of black plastic with a small rubber hose
leading to its front side. That's the bypass (throttle overrun) valve.

Anyway, a failed BPV (or its vacuum hose) is one of the more common
problems in a '91 200q with moderate mileage. The stalling that Steve
mentions precisely describes the most-often noticed symptoms of a
defective bypass (throttle overrun) valve. In fact, eliminating of
that kind of stalling is the main justification for the BPV's
existence, although faster turbo spooling between gear changes is
another benefit. When the valve (and/or its hose) leaks, the
result--in addition to the stalling problem--is often an inability to
reach or maintain maximum boost. Naturally, other hose leaks (like at
the ISV you mentioned) can cause boost loss, too.

When I bought my car 5 yrs ago (98k miles) the BPV and its hose were
well-toasted and became the first component to be replaced. This is a
timely thread for me in that the replacement valve has now
failed--after another 40K miles--and a new one will be installed in
the next day or two.

Phil
--

Phil Rose				Rochester, NY USA
'91 200q	(139K, Lago blue)
'91 200q   (64K, Tornado red)			mailto:pjrose at frontiernet.net