Date: Sat, 19 Feb 2005 20:28:11 -0800
Reply-To: Mark Keller <kelphoto@TELUS.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mark Keller <kelphoto@TELUS.NET>
Subject: Re: AFM ADJUSTING
Content-Type: text/plain; charset=us-ascii; format=flowed
Adam H. Behle wrote:
>Generally, the o2 sensor seemed to be doing its job-cutting out on
decelleration, showing more
>voltage under loads and up grades, etc. It did have a hard time
dropping the voltage after going
>over a grade or accelerating quickly.
>
>The initial "rich and sooty" position of the AFM wheel was about 7
clicks counterclockwise of the
>original position and gave a reading of about 800 mv while cruising at
3000 rpm on level ground.
>As I turned the wheel clockwise and monitored each new position while
driving,
>the engine seemed to be leaning out a bit with each click clockwise,
but the idle would stay
>around 2000-sometimes dropping slowly to 1000 or so. The voltage or
engine behavior did not
>seem to change whether the wheel was 5 clicks or 20 clicks clockwise.
I would get a reading
>around 500 mv at idle, but it was usually around 650 in normal driving
and at idle! I'll try some
>more tests and take more detailed notes in the next few days-the rain
has been pretty nasty.
>
>o2 sensor was cleaned before all this, but it's probably pretty gunked
up again after all this fooling
>around. It is the 3-wire type, and I connected the black 16G lead to
the red mm test lead and
>connected the other mm lead to ground. Unfortunately I have 2 nasty
hairline cracks on 2 of my
>exhaust headers-both on the right side. So perhaps all the o2 testing
is pointless until I replace
>(gulp) those headers. The van had been running fine (ok, a little
rich) before with the cracks
>though.
>
>I guess I'll try leaning out the engine a bit and start adjusting the
idle a bit. It is tempting to just
>order a rebuilt unit at this point and slap it in, followed by a new
exhaust-but I have a hard time
>justifying all that cash to fix a funky idle. I think I am finally
committed to a decision to keep the
>wasserboxer platform rather than a Subaru due to time, space, and
potential resale issues-so
>"investing" in this engine might not be so bad. Bostig Engineering's
miracle air box sounds really
>interesting as well if it actually materializes.
>
>Thanks again for your prompt replies,
>Adam
>
>
>
Hi Adam,
Well I would say that the 2000 rpm at idle is interesting, it fits the
theory that you were to rich on the spring, and that someone opened up
the air bypass to compensate for all of the extra fuel.. I would have
just immediately turned the big air bypass screw and see if it would
idle lower at the 850 RPM Range. If it did, it would indicate that you
were on the right track , and keep leaning out the AFM spring. BTW my
setting was 9 clicks, last one I did was 8, so you gettting to the
range. Don't let the high idle concern you when your leaning out the
rich cruise settings, it's a sign that your affecting the tune of the
Fuel injection.
Not that I'm saying give up on this AFM, but if you did get another
one, and your air bypass screw opened up and causing the high idle on a
properly tensioned AFM, you would still need to adjust it, if you
replace yours. so you might as well get some practice in fine tuning.
Typically the complaint on a bad wiper track/AFM is that a flat spot or
stumble occurs. This is somewhat problematic. If the afm tune is off,
it could cause a very similar sympton as a bad carbon track. So if you
had a stumble and it changes as your tune improves, I'd be less inclined
to write of the AFM.
Remember too that for now, the ECU is open loop, so no O2 data is being
incorporated into the fuel pulse map. Also that the exhaust cracks only
have an impact on your voltage, probley only slight to none as high rpm,
they may even close up when hot. The cracks probley would affect idle,
as less exhaust gas flow.
The .5 to .6 volt range sounds good, I would like to see you get below
.5 on cruise, but .5 is the goal. It's just that the AFM seem to a
load curve, when the spring tension is ideal. Giving a nice lean at
cruise, and nice power rich on heavy load. In fact on heavy load, I've
noted that the AFM open loop is more powerful that in closed loop, but
it's a small differance.
Mark
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