Date: Thu, 21 Jun 2012 15:35:21 -0700
Reply-To: neil n <musomuso@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: neil n <musomuso@GMAIL.COM>
Subject: Re: CO Adjusting Screw. PO Set it All The Way In? Base Setting?
In-Reply-To: <4FE395E5.5000709@turbovans.com>
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Cool. Thanks Scott.
My thought was:
foot taken off gas pedal, throttle valve switch and butterfly closes, IF
very little or no air came through the AFM air bypass, the O2 sensor would
sniff a rich mix and affect the ECU fuel shut off process. But with your
comments, I can see that once the fuel shuts off, it shuts off. I know
there's a test for this in Bentley but it requires a VW tool (resistor?) to
be inserted in the throttle valve switch plug. Maybe archives has info on
that.
When de accelerating, does vacuum created by engine pull the flap on AFM
open? Even if it does, I imagine wiper movement on the resistive strip
inside AFM is moot or ignored by ECU during de acceleration fuel shut off
mode.
O2 sensor, ignition parts, muffler (exhaust seals) are new. Maybe the
slight play I feel in the TB shaft is enough to cause an issue at throttle
valve switch. But this switch closes every time, engine off, throttle moved
by hand. I may wire in an LED and watch it while driving. A real world test!
Neil.
On Thu, Jun 21, 2012 at 2:45 PM, Scott Daniel - Turbovans <
scottdaniel@turbovans.com> wrote:
>
> personally I would not expect AFM mixture screw to have an affect on when
> fuel shut off occurs.
> My understand of that is, ECU cuts signal to injectors when throttle
> switch is closed and engine rpm is above whatever the threadhold rpm is
> ....like 1,50 rpm or whatever it is.
>
> I don't see how that might be related to mixture at the AFM.
>
>
> I do not like to see the AFM screw at either limit.
>
> not counting tail pipe emissions ..
> this often will work -
> Ignition can't be too advanced ...needs to be pretty close to spec.
> Idle switch must make contact every time throttle is closed, and that it
> makes continuity must be checked too , though I have not seen a micro
> switch fail to conduct .
> If you are not worried about tail pipe emissions,
> and there are no air intake leaks,
> and things like Temp Sensor II are doing their job right, ( and all
> ignition components - though for me , good Bosch igniton components last
> almost definitely. )
> 'usually' a combination of Air Bypass Screw on the throttle body, and AFM
> mixture screw setting will get a decent consistent idle, if there isn't
> something else messing things up.
>
> I have seen things like ...
> wonky Temp Sensor II that read right cold, and wrong hot.
> throttle switch not making contact - very common.
> exhaust leaks near an 02 sensor.
> and AFM's ....they get 'uneven' eventually ...like subtle uneven
> acceleration.
> I don't usually mess around with the insides of them.
> If money was no object, and we can get actual New ones, , I'd say 100K
> miles on an original one is plenty. 150K is plenty plenty.
>
> it's always worth it to try running with 02 sensor disconnected , as a
> test.
>
>
--
Neil n
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