No max boost - wastegate. Am I nuts?

Kurt Deschler desch at
Wed Sep 28 13:10:02 EDT 2005

A few other common low boost problems are the air temp sensor connectors 
(near the IC outlet), solder joints in the WOT switch, and bad connector 
on the WGFV.


> Message: 5
> Date: Wed, 28 Sep 2005 02:04:09 -0600
> From: barry at
> Subject: Re: No max boost - wastegate.  Am I nuts?
> To: quattro at
> Message-ID: <1127894649.433a4e79bb395 at>
> Content-Type: text/plain; charset=ISO-8859-1
> Update on turbo woes:
> The wastegate on the '87 5k, as I understand it, works basically by not opening
> until a certain manifold pressure is reached.  The pressure in the manifold
> overcomes the pressure of the wastegate spring plus an amount of pressure cycled
> in by the wastegate frequency valve, allowing the ECU to regulate the max boost
> the engine can get.
> My car only gets to 1.0 or 1.1 bar when it should be getting 1.4 bar.  The turbo
> system is capable of generating full pressure, as verified by plugging the lower
> wastegate hose-- car got to 1.5 bar before fuel cutout kicked in.  Just now I
> tested the WG by bypassing the WG freq valve and plugging the manifold pressure
> line into the top WG port (essentially both lower and upper WG hoses were
> getting the same pressure, so the WG shouldn't ever open, and the car should
> overboost.  It did).  So the WG will vent boost in the stock configuration, and
> hold boost to fuel cutoff when no pressure differential exists.  As far as I
> could tell, the WG is functioning properly.
> Then I ran the WG freq. valve test as suggested in the Bentley- It buzzed
> happily away as it should when the engine light blinked 4442, just as expected.
> So the Bentley would have me think the valve is good, it appears.
> As I am understanding things now, it would seem the WG freq valve is bad despite
> what the Bentley would suggest, or the signal getting to the valve isn't right;
> which could be a bad vac hose to the ECU or a maybe bad coolant temp sensor.
> Am I nuts?  Is there anything I'm missing here?
> Thanks for any pointers & BTDT
> =BB=

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