Date: Tue, 4 Sep 2007 03:39:07 -0500
Reply-To: John Rodgers <inua@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <inua@CHARTER.NET>
Subject: Re: It's time to hit that idle Stabilizer on the head!!!
In-Reply-To: <vanagon%2007090402435023@GERRY.VANAGON.COM>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
It sounds as if you and John Bange just about have a serious handle on
this little black box that causes so much trouble. It would be wonderful
if a modern replacement for that thing could finally be achieved. I'm
sure there are many of us less knowledgeable van owners that are sort of
holding our collective breath while this plays out. I know I am. I have
two vans and both boxes are crapped out. I don't want to install used
ones, since even used ones cost money and I don't like to install
crapola used parts. Bet I'm not the only one either.
Thanks guys, for all your hard work. We are anxiously awaiting the rest
of the story!
Regards,
John Rodgers
88 GL Driver X2
T.M. wrote:
> On Mon, 3 Sep 2007 22:33:14 -0700, John Bange <jbange@GMAIL.COM> wrote:
>
> >From his comments, I understand that the
>
>>> original boxes were analog, and jumped through considerable hoops to
>>> derive the signals needed to operate. The replacement digital unit that
>>> would use the IC's would have no such problems, and not be so
>>> problematic.
>>>
>
> AFAIK, the main thing that usualy breaks in those boxes is the output
> driver transistor, due to overheating caused by the ICV solenoid sticking
> (pretty much like a stuck electric motor), causing current overload and
> destruction of the transistor, sometimes also the current limiting
> resistor. The analog circuits seem to work fine.
>
>
>> Exactly. The old analog device manages to keep the engine at a certain
>> number of revolutions per minute, despite the inability to ACTUALLY COUNT
>> either revolutions or minutes.
>>
>
> No need to "count" - as I mentioned, it's full of analog op-amps, which
> are probably used as integrators ("counting" pulses) and oscilators (to
> generate the pusles to drive the ICV). Plain & simple good-old analog
> circuitry...:-)
>
>
>> Doing it digitally is a simple matter of a
>> program that loops through the following instructions:
>>
>> 1. measure time between coil "sparks" to get idle speed
>> 2. is idle too low? open ISV wider
>> 3. is idle too high? close ISV a bit.
>> 4. go to 1.
>>
>> The throttle switch throws it into a "standby" condition,
>>
> More importantly, it also puts the ECU in "standby" condition so it
> doesn't interfere with the ICSU (some signals go in parallel to both).
>
>
>> and the PS pump switch merely modifies what it considers optimum RPM.
>>
>
> Yep, so does the A/C sensor switch.
>
>
>> Easy as a walk in the park, really.
>>
>
> Once it's working of course...
>
>
>> I'm actually surprised they didn't just include this function
>> in the Digifant. It would have been so easy.
>>
>
> They should have. It's probably Bosch's trick to make more money (and VW
> too, also for replacement parts. Can you believe the ICSU costs more than
> the ECU?).
>
>
>> The project stalled on the one thing I couldn't figure out: how, exactly,
>> does the idle control unit operate the idle stabilizer valve? Having but a
>> voltmeter, I can only tell that it receives voltage when the ignition is
>>
> on.
>
>> Without some insight into how it's opening and closing the thing, I'm
>> stumped.
>>
>
> OK, I'll try to take a look and get you this info, but since my time is
> limited, help from the list would be good (that's why I wanted to put the
> photo's on the web). What is needed is to reverse engineer the output
> driver schematic and put a digital scope on the output.
> One of the problems I can think of is the mechanical design of a
> replacement device. Maybe piggy-backing on the original circuit board
> inside the original box using the same connector would be the easiest
> solution.
>
>
>> --
>> John Bange
>> '90 Vanagon - "Geldsauger"
>>
>
>
>
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