Subject: low boost

C1J1Miller at C1J1Miller at
Wed Aug 13 12:49:27 EDT 2003

Does your aftermarket gauge also show vacuum readings?  With the car off, does it read below 0 psi? Sensor
Altitude Sensor (F96)
The altitude sensor is located beneath the left kick panel, near the A pillar.  When there is a change in the air pressure, the barometric cell in the altitude sensor moves a sliding contact over a set of resistors.  This informs the ECU of the current ambient air pressure or altitude.

The altitude sensor is only used for boost pressure control.  At altitudes above 3,300 feet above sea level, the boost pressure is reduced as the altitude is increased.  The reason for this is to avoid over-revving the turbocharger.

If the sensor should fail, an altitude of 13,124 is assumed and the boost pressure is reduced to its minimum level.

Pics etc. here:


In a message dated 8/13/2003 11:21:41 AM Eastern Daylight Time, 200q20v-request at writes:

> Message: 2
> Reply-To: "Brandon Rogers" <brogers at>
> From: "Brandon Rogers" <brogers at>
> To: <200q20v at>
> Subject: low boost
> Date: Tue, 12 Aug 2003 14:08:29 -0600
> Organization: Terrix Financial
> This is a multi-part message in MIME format.
> --
> [ Picked text/plain from multipart/alternative ]
> HI guys-
> yeah I know--yet another low boost post to the list....oh well.  The patie=
> nt is an urquattro with totally stock 3B motor, except for a chip upgrade. =
> I live in Denver (~5300ft elev).  My Autometer mechanical boost gauge will=
> only show 15 psi of boost on 3rd gear acceleration runs, and I can see 16 =
> psi in 4th--but I should be seeing 18psi +.  I have swapped ecu's with anot=
> her chipped known good, WGFV, new BPV (tried 2 separate ones), new vac hose=
> s--also pressure tested system, no codes stored, new MFTS.  Due to the moto=
> r swap, I'm using a cone filter, however I have made a heat shield to separ=
> ate the filter from the turbo.  The one scenario I'm thinking is that maybe=
> my intake temps are too high b/c maybe my shield is too inadequate-so the =
> computer is keeping boost low???  For an intercooler I'm using the one that=
> came on European 20V urquattros.
> Any other ideas?  I've checked SJM and nothing jumps out at
> me.  Otherwise =
> it runs great--just down on power a bit.
> TIA-
> Brandon
> '84 urq 20V

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