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On 8 Jul 97, Woolston Craig wrote:
> I have experience the same thing in a '70 Sqback, '71 Fastback and
> '72 Fastback (not that body style has anything to do with it). I
> just assumed it was normal under the same assumption you made about
> the throttle contacts. My experience was that just off idle,
> espically when moving (~10-15 mph) it would buck and the solution
> was to speed up and then use the brakes sooner. The only question I
> have is that my cars appear to be running rich and I am experience
> the same problem?
Is it possible that your fuel pressure has been turned up in an
attempt to compensate? I think a fuel pressure increase would be
linear while I think the Pressure sensor response may well be non
linear. In the end we might find ourselves lean at one end and rich
at the other.
The effect that I suspect is that the brass bellows in the pressure
sensor has a very small leak, allowing the partial vacuum inside it
to slowly come up to atmosphere. This would lengthen the bellows at
all pressures which would mimic lower absolute pressure (greater
vacuum) in the intake manifold. Responding to this, the FI would
send what it thought was an appropriate amount of gas, which would be
too little.
The brass bellows always have a number hand-written on them in some
kind of black marker. Does anyone know what this number represents?
If it is a measure of some dimension when new, then it might be
possible to remeasure and correct the calibration for another 20
years.
Jim
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Melissa Kepner Jim Adney
jadney@vwtype3.org jadney@vwtype3.org
Laura Kepner-Adney
Madison, Wisconsin
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