Date: Wed, 11 Aug 2010 15:58:38 -0700
Reply-To: "Mike \"Rocket J Squirrel\"" <camping.elliott@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: "Mike \"Rocket J Squirrel\"" <camping.elliott@GMAIL.COM>
Subject: Re: AFM track cleaning wisdom
In-Reply-To: <ED524AE0A3DF400BB82F6E7EF0F504F0@TomYoungPC>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
As I mentioned, I had the thing open a few years ago and moved the wiper
to a fresh portion of the track. I did this as you describe: by ovaling
the mounting holes, so I phrased it wrong, I didn't move the wiper but
the track. My bad.
I've only put about 15,000 miles on the thing since, I doubt the wiper
has worn through the new portion of the track yet. But I will inspect
and report.
I'm following up on the mechanic's suggestion as he felt that the
symptoms I described last week (see "Mystery engine cutouts") may be due
to a bit of schmutz on the track.
Anyway, in Ye Olde Days when I was a broadcast engineer, we used to
clean the Shallco program attenuators (coined-silver contacts) with
Hoppe's gun oil. That's probably a bit gummy for a AFM potentiometer,
but there may be some other cleaner/preservative I can put on the track
while I have it open.
Mike S and David-The-B both point out that abrading the track with a
pencil eraser is dumb, dumb, dumb. Point taken. See their posts for
details.
To David, thanks for mentioning that capacitor -- yes, I have a 22uF
tant cap wired in to reduce wiper/track noise.
Just for the record, Richard-K asks for general AFM track servicing
information and says that he has "some `bogging' problems similar to"
me. I want to say to Richard that I would not describe the problem I had
as "bogging," more like an abrupt loss of power, mixture slamming toward
full lean condition, ignition continuing, then after 3 to 4 seconds,
abrupt return of full power.
Out of curiosity, does anyone know what the ECU tells the engine to do
if the AFM wiper loses contact with the track? Cut off fuel?
--
Rocky J Squirrel
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
Bend, OR
KG6RCR
Tom Young wrote:
> As I recall, and I may be wrong, the issue here with the AFM track isn't
> that it's dirty, it's that hours and hours of wear and tear at a
> particular spot actually result in the surface material being etched
> away, causing the ECU to think "Oh, the AFM's vane is closed!" and
> reacting accordingly. So I'm not sure that cleaning has much to offer
> here.
>
> I've had good results by opening up the AFM (air-cooled, and I'm
> assuming the water-cooled engine's AFMs are the same), removing the 4
> screws that hold the wiper circuit board, removing the circuit board
> itself and then ovalizing the 4 holes in the board that the screws pass
> through. You can then re-install the circuit board in just a slightly
> different position, giving the wiper a new track to pass over.
>
> Tom Young
>
>
> ----- Original Message ----- From: "Mike "Rocket J Squirrel""
> <camping.elliott@GMAIL.COM>
> To: <vanagon@GERRY.VANAGON.COM>
> Sent: Wednesday, August 11, 2010 2:30 PM
> Subject: AFM track cleaning wisdom
>
>
>> My mechanic dude suggested the the cause of the engine's periodic but
>> brief loss of power during grade climbs last week might be a dirty spot
>> on the AFM track and suggested gently cleaning it with a pencil eraser.
>>
>> I opened it once before, a few years ago, to move the wiper to a fresh
>> bit of track. I'll open it again to clean the track.
>>
>> Is the pencil eraser trick good enough, or would it benefit to use some
>> kinda cleaner?
>>
>> --
>> Rocky J Squirrel
>> 84 Westfalia: Mellow Yellow ("The Electrical Banana")
>> 74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
>> Bend, OR
>> KG6RCR
>>
>
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