Date: Fri, 3 Dec 1999 08:03:36 -0600
Reply-To: Marshall Ruskin <mruskin@PANGEA.CA>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Marshall Ruskin <mruskin@PANGEA.CA>
Subject: Re: Help
Content-Type: text/plain; charset="iso-8859-1"
This happens because the AFM is, according to the Bosch literature I read,
the master sensor for the fuel injection.
The AFM tells the computer (ECU) how much air is being "breathed" and this
information is used to roughly tell the ecu how much fuel to meter into the
fuel injectors.
This is further fine-tuned by the O2 sensor, to more precisely adjust the
amount of fuel injected.
Now, when dirt or a defect in the afm exists at a particular setting of the
AFM, the signal from the AFM will "jump around", which should not occur in
a properly functioning unit.
The ecu sees this "jumping around", and thinks that something is
dramatically wrong with the system - and begins to shut down the fuel, as it
thinks the system is flawed.
When that happens, the afm voltage will drop, because less air is being
forced through it. When that happens, the wiper or vane inside the afm moves
to a new position - usually past the area where there is a defect (dirt or
discontinuity).
At this new position - the afm does not present a noisy signal, so the ecu
thinks the system is back to normal again, and begins to properly supply
fuel - and you suddenly get power again.
You have just experienced a single "buck"!
Now, why these fixes work are for the following reasons:
1. Replacement - Obvious
2. Harness: An electronic filter that screens the AFM output signal
from quick changes - (like what a noisy signal has);
3. Capacitor: same thing - except homebrewed and much cheaper
4. Cleaning AFM: Removes cause of noisy signal in the first place, hence,
no need for a filter. I suspect, although I have no proof, that this will
extend the life of an afm, by removing abrasive elements.
Hope this helps,
Marshall Ruskin
>How and why does this work? I have the bucking syndrome (infrequently) and
>it is frustrating to try to find the source of the trouble.
>
>
>Marshall Ruskin writes:
>
>> I cannot help you with the head gasket problem, but I may be able to help
>> with the bucking.
>>
>> It is an extremely common problem, often, but not always caused by
>> electrical noise in the Air Flow Meter (AFM).
>>
>> The thing is, there are several similar ways to fix this:
>>
>> 1. Most expensive - replace AFM and pray that was the problem;
>>
>> 2. Obtain $150 US AFM harness from VW, and pray that it fixes the
>> problem;
>>
>> 3. Attach (solder) a 22 35V microfarad tantalum capacitor across pins
2
>> and 4 (somebody correct me if I got the pins wrong) of the connector to
the
>> AFM ($0.25 - $1.00) - no need to pray;
>>
>> 4. Carefully pry the black plastic lid off of the AFM, (may need to
cut
>> the silicon seal), spray electrical contact cleaner liberally, move wiper
a
>> few times, let dry. Avoid touching contacting surfaces with your fingers,
or
>> getting dirt, dust or oil inside. This is my personal favorite. I pray to
>> MTNGAL who discovered this trick - works great, solves the problem, and
is
>> very easy.
>>
>> Hope this helps,
>>
>> Marshall Ruskin
>> 84 Westy Iron Igloo
>> Winnipeg, Manitoba, Canada
>>
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