Re: Dead on the Freeway

["Melissa & Jim" <jadney@vwtype3.org>]

On 29 Oct 97, William Falkenbach wrote:

> I did pull the pressure sensor out and check between
> terminals for resistance. Between 7 & 15 is about 90 ohms but no
> reading between 8 & 15. I read where it is supposed to be about 350
> ohms. Checked with a vacuum pump and it holds vacuum. Went to
> junkyard, tested 12-15 old pressure sensors, and except for the fact
> that some did not hold vacuum (obviously no good) none of the others
> gave me a reading between 8 & 15! Strange. Could they all be bad or
> some misinformation?

Sounds like you're checking the wrong terminal pairs.  The PS is a 
transformer: it has a primary and a secondary which have no DC 
connection between them.  Of the four terminals on the unit, the two 
inner terminals are one winding and the two outers are the other 
winding.  One winding has about 90 ohms DC resistance and the other 
has about 350 ohms.  There should be "infinite" resistance between 
windings and between either winding and ground (the body of the PS.)

If that is the way you checked it then you have a bad unit, but you 
mention terminal 15 in BOTH measurements above, which can't be right,
and I don't believe ALL the junkyard units could also be bad.  I've 
never had a PS that failed with an open winding, but I'm sure it 
could happen.  My guess is that you're doing the wrong test.  You'll 
have to tell me. 

Also since you can`t get new ones, what about
> from a 914 1.7l and adjust with the screw. Seems there is more of a
> market for parts for 914`s than TIII`s. ANYBODY HAVE A GOOD PRESSURE
> SENSOR ONE AND WILLING TO SELL IT?

I recommend that you replace only with the correct sensor.  I'm sure 
I have a good one here that I would be willing to sell.  What year is 
your car?  MT or AT?  Or send me the # on the brain to make sure they 
go together.

Jim
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       Melissa Kepner                                    Jim Adney
                             Laura Kepner-Adney
                         jadney@vwtype3.org      
                             Madison, Wisconsin
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