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Date:         Thu, 17 Feb 2005 15:16:39 -0500
Reply-To:     Sam Walters <sam.cooks@VERIZON.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Sam Walters <sam.cooks@VERIZON.NET>
Subject:      Re: strange bucking problem w/ '84 vanagon wbx
Comments: To: Zoran Mladen <zmaninco@YAHOO.COM>
In-Reply-To:  <20050217184808.91848.qmail@web21128.mail.yahoo.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Kim Brennan once stated in a list email or a pmail to me that he had seen the insides of the VW AFM harness and it had more electronics in it than just a capacitor. He didn't elaborate and I assumed that this was correct. IIRC, both work to smooth out the signal from the AFM to the ECU so that the ECU gets a steady signal and doesn't cut out from thinking the lack of a signal from the AFM or from getting one outside the operational parameters. AFM's can get worn spots on the track which are essentially a dead spot from which no signal, or an aberrant signal, is generated. Signals outside the operational parameters can cause the ECU to stop the signals necessary to operate the van, hence it cuts out for a brief period (or longer with some other problems). This can also be fixed by moving a board inside the AFM so that the moving arm tracks on a different part of the board making an arc without passing over worn spots.

A number of folks have used both the capacitor fix and / or the VW harness and found that it didn't solve their van's "bucking" problem. Many times a bucking, or intermittent operation, problem is not caused by the AFM, and therefore, doing something to the AFM will not eliminate the problem. It can be a vacuum leak, or a problem with another sensor in the FI system - e.g., the Temp II sensor, the O2 sensor, the idle control unit, etc.

Similarly, if the O2 sensor is not the cause of an operational problem, then replacing the O2 sensor will not fix the problem. You have to replace the part(s) responsible for the problem.

Careful attention to the exact circumstances under which the intermittent operation comes and goes helps to identify which component has failed or is failing. However, sometimes it is something as simple as a faulty ground connection or bad wiring to a component such as the O2 sensor.

I cannot remember anyone reporting that the capacitor fix did not work, but that the bucking problem was then cured when they used the VW harness, having made no other changes to the FI and ignition systems. My memory could be wrong, but I try to pay close attention to posts of that nature. Maybe someone has had or remembers a report of a contrary experience.

Sam

Sam Walters Baltimore, MD

89 Syncro GL 85 Westy Weekender

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