Low Turbo Boost '86 5KCSQ, WG operation

["Scott M." <scottmo@teleport.com>]

Robert,

> I've been trying to sort this on my 5kt the last few
>days. I have a VDO  boost gauge plumbed in as per the
>Bentley. It reads 7 psi when under full boost on 80 deg
>day. Within spec apparently. When the line from WG to freq
>valve is removed and plugged, it does 8 psi- so the WG
>allows *more* pressure this way? Some text deleted.
>  I also thought disconnecting the WG solenoid would lower
>boost. I'll be  following this thread carefully...
> Rob 

As Orin mentioned the symptoms described
indicate that the ECU is not attempting to add pressure to
the top of the  WG diaphragm using this WG solenoid. 

The full throttle switch must be working correctly to
signal the ECU that the throttle is open past the 2/3 point
so it can control the boost using the WG solenoid. As Phil
P. mentioned, a LED light can be connected across the WG
solenoid connections to verify the ECU is correctly
operating this solenoid while the vehicle is driven at WOT.
(Scott Justusson aka PDQSHP suggested this LED test several
years ago). 

Many  of the '86-88 5000T/Q's and 200T/Q's I have worked on
had intermittent/defective full throttle switches due to
cracked internal solder connections. Testing these full
throttle switches that have cracked internal connections
with an ohm meter often shows the switch to be ok one
minute and then defective another time. The ECU fault code
diagnostics may not pick up this intermittent poor
connection. The idle portion of the switch can have the
same poor connection problem which results in an idle speed
that goes up and down erratically. The plastic cover can be
cut off this throttle switch and the internal connections
can be re-soldered.

I suspect that there are many '86-88 5000T/Q and 89-90
200T/Q vehicles around with defective throttle
switches but the owners don't know because the ECU only
adds only ~ 0.1 bar using this WG solenoid at lower
altitudes. 

The Audi service training information indicates that the WG
solenoid system will not function if the following
conditions occur: the engine temp exceeds 247 F, if a fault
develops in the manifold pressure sensor (inside ECU), if
the specified boost value has not been reached with 3
seconds of system operation, or if the ignition timing is
being retarded the maximum amount (7.8 degrees) because of
engine knock. A defective knock sensor/wiring or a
defective overtemp switch should also prevent the ECU from
adjusting the boost using the solenoid. Orin can likely add
more detail to these items above.

HTH
Scott M.