Jim Adney jadney at vwtype3.org
Thu Apr 27 15:08:51 PDT 2017

On 27 Apr 2017 at 16:22, KENNETH ROGERS wrote:
> The pressure sensor on a 1971 vw Type 3 FI squareback automatic, 1640cc stock everything. After setting fuel pressure regulator to 28 pounds and making sure throttle valve switch is in correct position and everything is correctly adjusted, can I fine tune this pressure sensor? It is running rich. 
> I have monkeyed with this in the past with a sick running motor so it is out of adjustment. 
> Who has experience on this? I found nothing in the books about adjusting it. Is this where I find a '14 to 1' or higher air ratio at 5000 feet altitude (I live at) using my Sun tail pipe sniffer? Or just find the sweet spot in dialing it in? 

The '71 pressure sensor has 3 different interacting adjustments. There's no 
way to guide you to a reasonable conclusion. Messing with these is 
ALWAYS a mistake. I can set yours back to stock, and that's where you 
should leave it.  

There is one thing you should check on your pressure sensor. That year has 
a diaphram which may break after all these years. You should check yours 
by attaching a hose to it and sucking on the other end. It should hold 
vacuum. If it leaks just a bit, you might only need a new O-ring, which I stock. 
If it leaks badly, look for an untampered one of the same part number. I may 
have one, but they are expensive.

I've tried to make replacement diaphrams, but without success so far. Stay 
tuned for that. A cracked pressure sensor diaphram will make the FI run 
extremely rich.

The 1640 cc engine changes the FI calibration. As a first approximation, you 
should increase the fuel pressure by the ratio of the increase in 
displacement: 30 psi x (1640/1596) = 30.8 psi, which is not much of a 
change. Since you're already running rich, you should probably figure out 
what else is wrong (tampered pressure sensor!) before changing the fuel 

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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