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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 > >


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