Update to my MPS web page

[pbanders]

Well, I've just added the first pass at an electronic calibration method
for the MPS:

http://members.rennlist.com/pbanders/manifold_pressure_sensor.htm

Navigate to the "Electronic Calibration Method" link to see it.

A few comments...

It's a fairly complex procedure that requires investment in about $225
worth of equipment. I don't expect that many will attempt it, but I think
it would be reasonable for a local 914 club to buy the stuff for others to
use. Anyone here in the Phoenix area is welcome to email me and set up a
time to come by and I'll check (not calibrate!) your MPS for you. However,
I'm not in the business of calibrating these beasts, I simply don't have
the time. I provide the web page so that others can learn to do this for
themselves.

Of course, if you piss and moan enough, yes, I'll help you. :-) But you
already knew that....

One thing that's immediately apparent from looking at the calibration
table is that Bosch's "method behind the madness" becomes apparent. You
will note that the calibration value at 15 in. Hg for all of the units is
essentially the same. The only difference between the units is the
calibration value at full-load. This permitted Bosch to manufacture and
calibrate all of the cores EXACTLY THE SAME. The only differentiation for
each specific part number is the full-load setting. This allowed Bosch to
grab units, install the full-load plug and set the value, then stamp the
part number. A very efficient way to do it.

It also explains something that all of us have known for a long time,
which is that you can take just about any MPS that holds vacuum and use
it, and your car will run pretty well. The slope of the part-load
characteristic is not settable (except by modifying the tensioning spring
or the aneroid cells - and there are some non-914 units that do differ)
and varies by about +/- 5%. Therefore, if the value at some reference
value (e.g. 15 in. Hg) in the linear region is the same, then the
part-load characteristics are the same for all three different 914 MPS's.
However, the full-load mixture will likely be wrong (lean/rich, depends on
the swap). As a result, recalibrating a stock 914 MPS for a different
stock 914 application is fairly simple - you remove the epoxy, then turn
the full-load screw to the correct setting (as determined by the
calibration value of inductance), then seal the screw. That's it.
Adjusting for performance modifications, however, is more complex.

I'm still looking for more NOS units for building my calibration table,
which has a woefully small sample size. I'll take rebuilt units, too, but
I have less assurance that they are properly calibrated to start with (ask
John Larson). The parameter extraction is non-destructive and I'll send
the unit back to you promptly. And you'll get credited on my page with
furthering the cause of keeping our 914's alive!