No max boost - wastegate. Am I nuts?

[barry@moonbeast.com]

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=







Quoting barry at moonbeast.com:

> I'm trying to track down the low boost issues in my '87 5k--
> 
> It basically won't boost past 1.0 bar.
> 
> My vac hoses all look good, lots of new stuff.  I just tested that by
> plugging
> the lower wastegate hose, and voilá, suddenly I'm getting full boost up to
> 1.5
> bar and fuel cutoff.
> 
> Does that mean a bad wastegate diaphragm?  What else could it be?  I tried
> removing the upper wastegate hose at the WG frequency valve and applying
> vacuum
> to it- I got to 11.5 " Hg before it wouldn't hold any more.  How much vacuum
> should it hold, or is that even a valid test?
> 
> What else could it be?  I think I'm getting close here...
> 
> Thanks!
> =BB=
> 
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