[T3] MPS calibration

[Bryon Garvin]

Hi all -

Well my friend showed up today to take the inductance readings from my PS
and then attempted to adjust his so that they match.  His '71 Fastback MT/FI
has not been running all that well.  It died on a long trip and a pressure
sensor from a late 60's model was installed at a shop and got him running
again....but not great.  He limped home and has been trying to figure it all
out ever since.  Because the "C" sensor would no longer run his car, and the
one the shop put in did allow him to drive, he started by looking at the
sensor.

He came today and we pulled MY working sensor (we both have 71 Fastbacks
MT/FI).  First thing we did was use an inductance meter to measure the
values on both inner and outer pins at zero vacuum.  We then used a hand
vacuum pump to take readings again at 4 inHg and 15 inHg.  We were following
the instructions on this site:

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

We then took HIS sensor and removed the screw.  With me holding the
inductance meter probes on the pins, he turned the inner and outer screws
and made the values match what my PS readings were.  When we were done, his
values were exactly like mine.  It took some time as each screw affected the
other and we had to go back and forth.  This brings me to something Jim said
one time and I wanted to ask you, Jim, what you meant:

".... the 3 adjustments will have to be done in some particular order to
work.
The problem is that the adjustments affect each other, so I need a
proceedure that gets it right in a finite amount of time."

Now that I have tried to do this, why does it all have to happen in a finite
amount of time?  I don't understand that.  Can you elaborate?

We put the sensor in his car, and well....it didn't run the car.  It barely
started and it sure didn't idle.  So he went home with the newly "tuned"
sensor in his hand wondering why it all didn't work.  I'm no help!  I was
just watching and helping take readings.  So, he's kind of back to square
one.

But I did want to post our procedure and results for anyone that was
interested.  And Jim I'd love to hear your thoughts on what we did and why
it didn't seem to work.

One other note of interest....I have 3 "C" sensors that are on my shelf.
 Since Larry was here with his measuring equipment I figured I'd put them
thru the tests and see what the values were.  Months ago, they all seemed to
hold vacuum when I sucked on them with a new piece of hose.  One of them
clearly was worse-off than I thought.  With a hand pump, we applied 15 inHg
and it slowly dropped in a matter of 8-10 seconds back to zero.  But the
other two held strong.

Out of the 2 that DID hold vacuum, one had inductance values nearly
identical to the values of the working sensor in my car.  The 2nd one had
values that were nearly HALF of what the unit in the car read.  So, what
does this mean?  I have no idea :)

Anyway, our findings are in this spreadsheet if anyone wants to take a look:


https://spreadsheets.google.com/ccc?key=0AmRobzkiJkYhdGx1aVF3TXpHV2xoaEVFS21oZlZpSnc&hl=en&authkey=CJucx48O

Thanks,

 - Bryon, '71 Fastback


On Tue, Dec 28, 2010 at 8:01 PM, Bryon Garvin <spinningrooves at gmail.com>wrote:

> Hi all -
>
> I'm trying to help a friend who wants to attempt calibrating his MPS.  He
> believes that his needs adjusting even though it holds vacuum.  He is
> consulting this website: http://members.rennlist.com/pbanders/manifold_pressure_sensor.htm#Calibration
> Curves<http://members.rennlist.com/pbanders/manifold_pressure_sensor.htm#Calibration+Curves>
>
> He's got a 71 sensor (Bosch 0 280 100 007) which is not listed here and I'm
> asking to see if anyone happens to have the data for this sensor, like is
> listed below in the table, so that he can do the 0 in.Hg, 4 in.Hg, and 15
> in.Hg measurements and make calibration adjustments.
>
> He lives an hour away and would like to come take the measurements from my
> sensor since I have the same one...but if this data is out there, it would
> be a lot easier to just get him the information.  Additionally, who is to
> say that my sensor is even going to still be "spec"?
>
> Below is the table, I hope that it comes thru the email looking correct.
>  If not, it's in the link above if you scroll down to "Calibration Values
> Table".
>
> Any help greatly appreciated.  And I believe he is still on this list (not
> totally sure) so he might even see the replies, otherwise I will get the
> info to him.
>
> Thanks very much for any help,
>
>  - Bryon, '71 Fastback
>
> Calibration Values Table
>
> *Bosch p/n*
> *0 280 100 027**0 280 100 037**0 280 100 043* *0 280 100 049*
>
> *Application*
> Not sure 1973 2.0L 9141974-1976 2.0L 9141970-1973 1.7L 914
>
> *Sampling*
> based on 1 good OEM non-rebuilt unit based on 1 rebuilt unitbased on 2
> rebuilt and 1 good OEM non-rebuilt unitsbased on 1 NOS unit *Vacuum Level*
>      0 in. Hg1.32 H 1.44 H1.39 H1.34 H4 in. Hg 1.17 H1.26 H1.18 H 1.15 H15
> in. Hg0.72 H0.72 H 0.71 H0.71 H
>
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