Date: Mon, 9 Jul 2012 12:51:08 -0400
Reply-To: Larry Alofs <lalofs@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Larry Alofs <lalofs@GMAIL.COM>
Subject: Re: At Idle: AFM Flap, CO Screw Relationship. Explanation Found
In-Reply-To: <4FFA4274.3010100@turbovans.com>
Content-Type: text/plain; charset=ISO-8859-1
Scott;
One of the main points that David was trying to make is that
inexpensive analog meters have too low an impedance to measure the
output of an O2 sensor. They need too much current to operate and the
sensor produces a volt or so, but a very small current.
Imagine trying to measure the pressure in a small diameter brake line
with a pressure gauge that allowed fluid to escape from the system
thru a half inch opening.
A DVM generally has a high impedance (uses very little current to get
its voltage measurement) but does not update quickly or smoothly and
is therefore hard to interpret in this situation. An oscilloscope
will work, but is expensive and bulky.
What we need is an inexpensive o-scope attachment for a laptop.
Would not need high frequency response by today's standards, just
cheap and rugged.
Larry A.
On Sun, Jul 8, 2012 at 10:31 PM, Scott Daniel - Turbovans
<scottdaniel@turbovans.com> wrote:
> Inexpensive small analogue meters are like, only 5 or 6 bucks these days.
> two gallons of gas about.
>
>
>
> On 7/8/2012 11:48 AM, neil n wrote:
>>
>> Good to know.
>>
>> Since I moved the AFM wiper to a new portion of resistive strip, I
>> kind of assumed there would be no drop outs. Besides; moving the wiper
>> did not change how the engine ran.
>>
>> Sure wish I still had my old $9 Radio Shack analogue meter!
>>
>> Neil.
>>
>>
>>
>> On Sun, Jul 8, 2012 at 11:35 AM, David Beierl <dbeierl@attglobal.net>
>> wrote:
>>
>>> At 02:10 PM 7/8/2012, neil n wrote:
>>>>
>>>> With my DVOM, I'd see the value change at a more or less "even" rate
>>>> when slowly and evenly moving the vane.
>>>
>>>
>>> The ideal tool for this is a scope. Analog meter with a twitchy needle
>>> is
>>> next. I'd rate most DMMs essentially useless for it unless they have a
>>> fast-responding bar-graph display. The normal 2-3 updates per second
>>> really
>>> can't show you little dropouts unless you're moving the vane with a
>>> micrometer screw or something like that, .....
>>> I'm going to make a wild guess that
>>> a typical DMM is only actually looking at the input less than a quarter
>>> of
>>> the time.
>>
>>
>>
>> --
>> Neil n
>>
>> 65 kb image Myford Ready For Assembly http://tinyurl.com/64sx4rp
>>
>> '88 Slate Blue Westy to be named.
>>
>> '81 VanaJetta 2.0 "Jaco" http://tubaneil.googlepages.com/
>>
>> Vanagon VAG Gas I4/VR Swap Google Group:
>>
>>
>> http://groups.google.com/group/vanagons-with-vw-inline-4-cylinder-gas-engines
>>
>
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