[T3] TB info?

[Max Welton]

Max


On Sun, Mar 13, 2022 at 10:18 AM Jim Adney <jadney at vwtype3.org> wrote:

> On 13 Mar 2022 at 0:58, Max Welton wrote:
>
> >> So this TPS does not have the functionality the megasquirt needs. I can
> >> adapt a modern 3-wire like I did before.
> >>
> >> https://www.thesamba.com/vw/gallery/pix/2270220.jpg
>
> >Like you did before? Is this a 2nd car? What does the megasquirt need?
>

Yes, new car. This engine was in my rusty 68 squareback and is now being
stood up in my "new" 67 fasty. The 68 has "returned to the earth" but I
saved many good parts for the fastback. The TB was always an issue. I also
have to examine the AAR and the idle valve too.

I fit up a 3-wire Bosch TPS to the 68s TB. If anyone cares, I can provide
details.

MS wants a TPS that is essentially a rheostat with the center pin being a
wiper that moves from one end of the resistor to the other. MS determines
the absolute throttle position based on the resistance between pins 1-2 and
2-3. MS also computes the rate of change (TPSdot) which can be used for
acceleration enrichment. Another TPS dependent feature MS provides is
"flood clear" which allows cranking with no fuel when the throttle position
is above a certain value.

I particularly like that throttle position is included in the logs.


> >> Now, how about the sensor that comes in from the left side? That is a
> >> thermistor, right? Any chance you have some data points I can use to
> >> calibrate it?
>
> >IAD temp sensor:
>
> >    860-1200 Ohms at 14 F
>
> >    250-340 Ohms at 68 F
>
> >    90-130 Ohms at 122 F
>
> >Cyl head temp sensor
>
>    >  7-12 kOhms at 14 F
>
>     > 2-3 kOhms at 68 F
>
>     > 680-1000 Ohms at122 F
>
> >There's a rather wide range/tolerance on these, but note that if you plot
> them
> >on semilog graph paper, you get a straight line. That is helpful if you
> want to
> >predict values at intermediate or warmer temps.
>
> >> https://www.thesamba.com/vw/gallery/pix/2270218.jpg
>
> >I have good temp sensors if you need a better one
>

Thanks. Let me see how well this one works.

Max
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