Re: Weird scary boost fun...

[EICHSTEV@aol.com]

Alex wrote:

> In order for
> the system to get "stuck", the boost MUST go over 1.1 bar for about 2-3
> seconds.  In other words, you have to be driving fairly aggressively to
begin
> with.  Then the gauge drops back to 0.8 and stays there regardless of
> throttle position or engine RPM.  
-CUT
> I am thinking it might be the pressure sensor in the engine computer box.
>  Does anyone know how this thing works and is it replaceable?  Is it
> solid-state or diaphragm and how should it work normally?

I'll bet you a Fat Tire (beer) that the there is a crack in the vacuum line
going to the ECU, probably right where  the cloth-covered rubber hose is
clamped at the intake manifold.   Boost opens the crack, vacuum pulls it shut
again. The cloth holds it together so its hard to find.  Must be a small line
that is broken/disconnected and keeping the ECU from knowing what the
manifold pressure is.  If you had a large leak (like IC to throttle body),
the display would be correct and you wouldn't get much boost. 

I doubt _very_ much you pressure sensor is bad.  They either work or they
don't and generally fail reading either full high or full low, never
atmospheric.  BTDT, I've repaired five Audi ECU's with bad MAP sensors, but
have never seen a failure such as you describe.  

Try the cheap stuff first.  HTH!

Steve Eiche
'82 Not So Ur q 3B to be