[T3] MPS calibration

[Jim Adney]

On 3 Jan 2011 at 22:55, Keith Park wrote:

> Our 72-3 PS's have diaphragms too don't they?  Im told by Ray Greenwood that
> they all do except the pre-70 units.  I cant remember what the late ones had
> in them.

No, only the '70-1 Type 3 PSs have the diaphrams. The diaphram type 
PSs are easy to pick out; just look for the 2 vent slots in the 
cover.

The diaphram serves a full load (wide open throttle) enrichment 
function. That was controlled by the pressure switch in '68-9, the 
diaphram in '70-1, and taken over by the 5th pin on the TVS starting 
in '72. I suspect Bosch figured out that this was a weak point in the 
design and moved it out of the PS after just 2 years.

The diaphram continued in some D-Jetronic cars after '71, so that's 
probably what Ray is remembering. I don't know why Bosch continued it 
in some cars and eliminated it in others, but Type 3s may have been 
the Beta test for other models. It may be the same reason Type 3s got 
D-Jet 2 years before anyone else.

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