[T3] '73 Idle Test

[Jim Adney]

On 27 Aug 2019 at 11:01, William Jahn wrote:

> I removed the temp or thermal switch from the cold start long ago. At one
> time when I still had the cold start valve plug connected I ran a wire to
> a switch on the dash so I could ground the cold start so I could use it at
> will yet it caused a rich cold start. I keep the cold start valve
> unplugged just the fuel line on it 

Okay, so to do the check I suggested, you would have to plug the CSV back 
in and then check the voltage on the wire that used to go to the temp switch.

Once you've done that, I'd suggest that you reconnect the wire to the temp 
switch and unplug the CSV. I just hate to see uninsulated wires left dangling, 
and there's no point in disconnecting both plugs.

FYI, on my '73 both plugs are connected. That still leaves the CSV disabled 
down to about 14 F, which is probably lower than your car will ever see.

>  I'll check to see if the other wire believe it's #18 on the ECU is hot
> when not cranking it also ends up in the test connector there is a + there
> and it is hot off the battery and #50 . I do know at the test plug + is
> hot all the time. If 50  is hot all the time then that's the problem

Yes, wire #18 is the one. I don't think it goes to the test connector in '73, 
although it did in late '71 and all of '72. (I suspect that VW eliminated those 
connections when they realized that running iginiton and starter wires to the 
test connector made hot wiring those cars easy!)  

Wire #18 gave the only source of extra enrichment in '68-9, unless M229, 
cold start valve, was installed. I believe that wire still gives extra enrichment 
in the later cars in the temp range down to where the temp switch enables 
the CSV.


> On the temp sensors.
> Yesterday working it the garage in over 100 degrees I removed TS2 and
> found it was a VW # 022 906 041 Bosch # 0 280 180 012 that was used for
> buses and T-4 . from what I could find a T-3 should have a bosch 0 280 130
> 003

003 was the part for '68-9. 012 is correct for all later years. As far as I can 
tell, the only difference is the length of the wire, since that wire had to be 
much longer in '68-9, when the sensor was mounted under the #4 exhaust 
port.

My impression is that ALL those temp sensors have the same resistance vs. 
temp characteristics. It's interesting that the 012 was sometimes labeled as a 
311 part and later also sold as an 022 part. I didn't know that.

My Bosch book calls out the 012 as correct for all aircooleds from '70-on, 
plus '80-3 Vanagons (were those still aircooled?) It calls out the 003 for 
'68-9.

You can interchange those, but you'll have excess wire one way and have to 
make a wire extension the other way. Most of the early FI engines have been 
rebuilt by this time and had a replacement head installed that allowed 
installation of the temp sensor on top, which is a MUCH better way to do it. 
Clearly, VW and Bosch were learning how to do this in the first 2 years. 
What's amazing is how well it worked, even then. I'd love to hear the story of 
their pre-release testing program. They must have had FI cars driving 
around Germany for a year or so, just to work out the alpha and beta bugs. 
We can find photos of TPSs with 3 terminals in some of the literature. Those 
were never used in production, so they must have been prototypes, used on 
some of the test cars.

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