Re: Low boost in 91 200q? PT swap ramifications...

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

Sargent Schutt wrote:
 
> I do have a boost problem, though. As follows: I had my TAP chip updated to the 2.5 bar pressure transducer (PT) and, in conjunction with the stiffer TAP spring (there from the start - not new), I get between 1.8 bar and fuel cuttoff, depending on how far down I screw the spring (mit allen-key adjustment under WG cap).

I don't think you have a boost problem, I think you have a calculation
problem with the stock boost gauge. With the 2.5 bar PT installed,
multiply the readings on the dash gauge by 1.25, I would recommend using
the stock WG spring adjusted as it came from the factory. Your 1.7 gauge
reading is actually 2.13 bar but seeing as the stock gauge is not all
that accurate, and can be a little slow to respond to rapid boost
changes, you are more likely seeing the 2.25 bar (18 psi) that this chip
set produces with the 2.5 bar PT installed (depending on air temp/fuel
etc). 

The 1.9 bar reading you were getting with the stiffer WG spring and the
cranked down spring perch corresponds to ~2.38 bar (~20psi) but again if
the stock gauge is off at all you may be getting even more than this.
You really should have a good analog boost gauge installed to get a
better idea what your boost is running at.
> 
> So, I decided to run the stock spring, since this is really what the
> code was designed for, along with the 2.5 PT. After the swap, I get 
>only 1.7 bar max, even though I have screwed the spring down as hard as
> the allen key will let me (I did this to compensate for 'tired spring'
> disease, what with the 175k I  have on the car).
> 
> Is this gauge a relative instrument? EG is it deriving boost values from the ECU, or from the vac line direct? 

The dash computer which drives the boost gauge receives a voltage from
the ECU from ~0-5 volts and with the 2.5 bar PT installed, this boost
gauge is not reading correctly.

HTH
-- 
Scott Mo.
1989 200TQ
1988 5000TQ
1966 VW Beetle
http://www.teleport.com/~scottmo