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RE: [T3] Low Voltage

On 16 Jun 2005 at 7:14, Mark Davis wrote:

> So that means it isn't a matter of the cold start alone, but most likely the
> time the injector is on. 

That's correct, and for 2 reasons. The problem occurs even in cars without the 
CSV, and, for those cars which have the CSV, the CSV is wired in such a way 
that low voltage could only reduce the amount of time that the valve is open 
(although my guess is that the parts were designed carefully enough that there 
is actually NO effect at all.)

> This will now bother me until I get a schematic and figure out
> how it works. Anybody know if one is available anywhere? 

I think there is one out there for a D-Jet 914, but the only type 3 one I've 
ever seen was at the UW Engineering Expo circa 1970, when this was State of the 
Art stuff. Someone there had worked out one by hand from an early brain. This 
was at a time when Xerox machines were scarce and I never managed to get a 

Around that same time, someone had written a book with schematics in it which 
was scheduled to be published, and I had a copy on order thru JC Whitney. After 
about 6 months Whitney cancelled the order, and the story I heard was that 
Bosch had sued to prevent publication of their proprietary material. I don't 
know if this is actually true, but, to the best of my knowledge, no one has 
ever published any of these schemantics other than the 914 one above.

With your background, this just might be a good project for you.

> From physically looking at the electronics I would say there is probably a
> differential circuit that cuts on/off based on the difference in voltage at
> some point in the circuit. 

I suspect that it's more subtle than that. I expect that we'd find that one of 
the circuits just experiences a change of bias as the supply voltage changes, 
and that this results in several effects, including this one.

I'm guessing that there's a timing cap in there somewhere that is expected to 
charge up to a trip point and that the charging time determines the injector ON 
time. With a reduced system voltage, the charging time would be lengthened and 
the injectors would stay on longer. But that's just a guess.

Jim Adney
Madison, WI 53711-3054

List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org

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