[T3] Diagnosis help for a badly running 1971 VW 411

[Jim Adney]

On 14 Aug 2019 at 21:49, Keith Park wrote:

> ahh, yes, Full load enrichment,  the 2L 914 didnt use that, yep, folded
> back under the boot.

You sure? I thought everyone got that from '72-on. It was the shutoff on 
overrun that got disconnected for some markets. Read on for more 
confusion....

Looking closely at my Bosch literature from 6.74 it looks like ONLY Type 3s 
got the 5 pin TPS. Everyone else stuck with the 4 pin, which is consistent 
with Type 4s sticking with the pressure sensor with diaphram.

There is at least one inconsistency here.

All my Type 3 wiring harnesses lack wires #2 and #25. For '69-'71, there's no 
wire #14. That seems odd, because for '68-9 there appears to be a wire #14 
from the pressure switch ('68-9 only.) The Bently appears to get this right, 
showing that terminal 14 connected to a wire #34. Unfortunately, the Bentley 
only shows the '68-9 version with the special cold start valve and it's 
associated, extra complicated relay and wiring. I can't tell from that what 
eventually happens to #34. It must eventually get to ground or 12 V. My 
'68-9 harness has 2 wires to the ground connector, while the diagram shows 
only 1, there's no number visible there, but I'm guessing that the extra wire is 
#34.

The extra wire on the 5-pin, '72-3 Type 3, TPS is #14, and there's a note 
next to the wire listing for wire #14 which says, "(only in VW 1600 E as from 
8.71)". This is consistent with the fact that my '69-'71 wiring harnesses do 
not have a wire #14 stuffed into the brain connector, but this position has a 
wire starting in '72. Looking at the internals of several TVSs, I can see that 
this is the full load enrichment pin.   

For wire #17 there's a note saying, "(only connected in VW 1600 E and USA 
models of 411 E)". This is the shutoff on overrun contact.

I just now found another page in the Bosch lit just for 914s. It shows only a 4 
pin TVS. Is that what you have? That 914 E page shows no wires in 
positions 2, 14 or 25. Next to the wire listing for wire #17 it says, "(connected 
only in USA models)". As above, #17 should be the shutoff on overrun 
contact. If yours is disconnected, I'd try reconnecting it and seeing if that 
does anything that annoys you. [Bosch Note: for Brain 0 280 000 007, used 
in '69-71 Type 4s and 914s, which were all 1.7 L , wire #17 must NOT be 
connected.]  

While researching all this, I also took apart two 4-pin TPSs, 1 from a Type 3 
and 1 from a Type 4. While the connectors point in different directions, they 
are identical inside. I also opened a 5-pin Type 3 TPS to confirm which pin 
did the full load enrichment function.

The Type 4 TPS is available if anyone wants it. It's the '69-71 version, Bosch 
#0 280 001 007, used but fully functional.

There's also a page labeled, "Special models for USA and Canada" that lists 
3 emission control features that were used in '72 and '73. These were:

1) Additional combustion air during overrun for Type 3s, Type 4s, and 914s. 
Looks like this was for '72 only, but '73 MTs may have had it.

2) Disconnection of vacuum advance except in top gear for Type 3s and 
Type 4s in '72.

3) Exhaust Gas Recirculation for AT California '73 Type 3s only.

Unfortunately, while all the extra components are shown in the wiring 
diagram, none of the new wires have numbers on them.

What year were you shooting for with your Type 4 engine? There are lots of 
options listed here, with different parts for USA and Europe. 

Whew! This has been exhausting! I'm guessing that few of you read this, all 
the way to the end. ;-)

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