[T3] MPS calibration

Keith Park topnotch at nycap.rr.com
Tue Jan 4 16:42:01 PST 2011


That's what I thought, and why I always had to take everything Ray said with
a degree of uncertainty, I don't think he's aware of what we call our E
based system and that's pretty astounding considering what he knows about
the other D jet based systems. Perhaps putting the black caps on the D based
sensors confused him. Porsche ran the C based system thru 74, and I wonder
what the late Caddy's used?

Your system of calibration makes sense, but they are touchy.. and now that
everything is old the sensors might not be too well matched to our older
engines as they once were.  I know getting mine right was down to a 1/16
turn or less with the main mixture, even less with the inner stop and the
outer stop was less exacting.  That inner stop is the gotcha, it wont idle
right if its not adjusted right and if its just a little off Ive seen the
mixture spike lean by a couple points under high vacuum.

Id love to use the late E based system on my 2056, it eliminates the
transition problems that were never worked out on the early systems, and
with all that power the slightly less throttle response would not be an
issue.  What the issue WOULD be is weather I can stretch a pressure sensor
calibrated for a 1.6 liter to a 2.1  Id need an idle mixture adjustment too,
can I add that to the E type brain? Jim, how much adjustment range do you
think there is on the late sensors?  WHAT is adjustable? You have 3
adjustments on the C based units, each is rather important... how do they
control maximum lean on the late sensors? Since the full rich terminal on
the TPS does the max rich feature, how would I increase full load enrichment
on the late sensor so I wouldn't have a flat spot with a larger engine?

Oh boy. Now you've  got me started!!!

Keith




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.

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

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