Re: Pressure Sensor

[stans4@ix.netcom.com (Stan Schaefer)]

I ended up replacing my pressure sensor when I first got my '71
becuase the first owner couldn't keep his screwdriver off the
adjusting screw.  I guess you learned that it has a seal for a reason.
There should be somebody on the list that can help you out with a
replacement, but if they can't, you'll have to take the car into
someone that can put an emissions meter on it and adjust the screw for
best mixture.  This thing is very sensitive.  This will be complicated
by the fact that something else isn't working.  It could be a number
of items and you really need the Bentley and  Muir's Idiot's guide
before you can really start working on it.  Here's my checklist, in
order:

Hoses and seals, check for cracks, particularly on the injector noses.
Air leaking by can really upset things.

Your throttle position sensor might have some problems.  Check it by
leaving the ignition on and going back and pressing the throttle arm
slowly open.  You should hear about 20 clicks.  If not, you have some
problems either in the sensor, which is easily fixed or a busted wire
in the harness, which is more trouble to fix.  The clicks are the
injectors pulsing, kind of like an acceleration pump does on a carb,
it gives the engine an extra shot of gas.  There's two sets of
microswitch-type contacts in the unit, one is closed when the throttle
is closed and tells the control unit so, the other is in series with
the little wiper arm that you'll see in there and is open when the
throttle is closed and closed when you step on the accelerator.  The
trick is to get them adjusted so that open and close without either
being closed at the same time, kind of confuses the control unit.
Chances are you need to clean the wiper arm and maybe nudge it over
into a little different path.  I use relay cleaner sticks to do the
contacts and something like a pencil eraser to clean the wiper track.
I use some special contact grease(NOT dielectric grease) to lubricate
and protect the track after cleaning.  Things tend to get a little
oily in there after a lot of years.  You might also have a broken wire
in there, they tend to get crispy.  Before you get too excited and
start moving things all over, a little adjustment with these contacts
goes a very long way, we're talking fractions of a milimeter here.
Follow the Muir instructions for adjustment of the throttle position
switch, Yours is a '71 so you should be able to hear the click when
the throttle closed switch makes up.  Before you put it in check out
everything with the ohmmeter, I've seen some of the rivits get loose
on the contacts and you'll have a bad connection.  Ceaning followed by
a little drop of solder will fix it right up.

These two things are what usually happens with loss of power, but
while you're there, check your valves and compression too, might be
something unrelated to the fuel injection.  

Hope this gives you somewhere to start

Sat, 27 Sep 1997 14:20:31 -0400 (EDT), you wrote:

>Hi,
>Anyone know what a Manifold Pressure sensor costs? Mine is for a 71 FI 
>motor, the number on the sensor says 030.  I tested the pins with a ohm 
>meter, two outer pins 7&15 read 100 ohms, two inner pin 8&10 read 350ohms.
>I tweaked the little screw at the end and now can't remember how it's 
>supposed to be set. OOps. It runs like before but now it runs rich, smoky.
>The main prob still exists; loses power on hills. Could it still be the 
>man. pres. sensor? I'm at wit's end here as this prob has persisted for a 
>year. Two wasted trips to Reiner VW and one to Sartwell have proven 
>futile. At least Sartwell got it to run smooth again. Rainer didnt even 
>do THAT and said 'oh car runs fine now'. He couldnt have meant MY car.
>I need this car to run perfect, I am driving to Los Angeles then Seattle 
>soon but all will be bust if I cant get car fixed. 
>I have had this Fastback ten years and swear by it. I dont want to let 
>one quirk ruin an otherwise fine car.
>Car has 179K miles, motor and trans have 9K miles. If anyone in Wash DC 
>area is an expert, Im a paying customer.
>Frustrated isnt the word. 
>John 71 Fastback
>