Date: Sun, 19 Jan 1997 12:31:58 -0700 (MST)
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: gmillang@freenet.edmonton.ab.ca
Subject: Re: Airflow meter fix info wanted
Oops! Well I guess my first attempt didn't work (can't send
attachments?) So here it is again: this I found in the archives and it has
a good explanation of the capacitor fix. I did notice on my AFM that pin 3
is +5 v, pin 2 is the wiper and pin 4 is gnd, so connect the +ve cap lead
to 2, -ve to 4
>From virgil!qmmac.emu.com!steve_hoge@uu6.psi.com Mon Feb 26 12:32:08 1996
Date: 26 Feb 1996 09:47:34 U
>From: "Steve Hoge"
Subject: Digifant Missing - $100 Har
Reply to: Digifant Missing - $100 Harness workaround
To All:
Here's the info on the cheapie harness replacement from Lars Herrnsdorf in
Gottenborg Sweden, posted to the list last 11/17. His English is a
little
"quaint" but I believe it adds to the good homebrew flavor of his fix.
Good
luck!
--------------------------------------
My first experience related to the problem was when I drove on the highway
on a constant speed and after an hour or so my engine just suddenly lose
all power, and after I stop and start again it work fine , the same
problem that Derek has told about in the Technical bulletin TB#12 and
TB#13 he has put togeteher from VW information he has. I phone some
friends in Sweden and quite soon I understod that the problem was known as
well as very special.
This was back in 93.
It seems like that the fault first was found in Sweden but when reported
first didn't the german compane Boch belive that it was a problem with
the air flow meter but a local VW service person use a oscilloscope to
monitor the output voltage from the resistor wiper that measure the air
flow value during a long measuring time. And his work pays off; He found
out that if the engine runs for a long time very constant and specially
also when the weather type is little frosty then the wiper could start to
lose the electrical contact on the resistor trace (It is not to easy to
find the word in english, but I think you understand what I mean) and
the voltage starts to oscillate instead of have a relative stable value.
The DIGIJET (and probely DIGIFANT) electronically box accumulate this
oscillator voltage value , but after a while it thinks it is a malfunction
and shut of the electronic pulses to that control the gasoline flow to the
engine: the engine suddenly lose all power !!. When the engine is
restarted all memory in the control box is reseted and the engine runs
fine until the same situation happens again , that can take days, weeks or
may not happen again The solution ( (if the gurantee is passed and you
don't want to try the $100 version first )at least for a while ( if the
air flow wiper resistance trace is totally unconducting(worn out) then the
whole air flow meter has to be
exchanged)) is to stabilize the output voltage round its oscillating
average value., The air flow box connector has four pins. Between pin 1
and 4 is the NTC-1 resistor that measures the temperature inside the air
flow meter.
Between pin 4 and 3 is the Potentiometer endpoints and pin 2 is the wiper
of the potentiometer that moves by the air flow and also is the output
voltage signal that must not oscillate. The easiest way is to add a $0.5
25 V 10 uF tantal capacitor with its +side connected to pin 4 and its
common to pin 2 (who is the air flow voltage output) to stabilise the
voltage. Later Boch came out with the $100 box that I think more or less
make the same thing.
Practically I mount the capasitor on a two wire 15 cm cable that I solder
on the pin 4 and 2 (note the polarity) in the connector that mounts on the
air flow meter box on the top. and then taped so it was completely water
resistant and dust resistant.
I can only say that I have not have the problem ever since. but You never
know if this fix was the whole solution for the engine power lose. God
Luck!!
If it not works , don't blame me, if it works use your other $ 99 to
something more fun!
GARY MILLANG email: gmillang@freenet.edmonton.ab.ca
'85 Westy 180K km
On Thu, 16 Jan 1997, Johan Nyberg wrote:
> Hello, I saw references to stabilizing the airflow meter's behaviour with a
> capacitor. As I recently joined the list, I can't find the original
> message, or the adress of the "Scott". Please help, someone.
>
> Johan Nyberg, Sodertalje Sweden
> '86 Caravelle C
>
>