Date: Wed, 14 Feb 2007 13:53:12 -0800
Reply-To: jon <jon@KENNEKE.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: jon <jon@KENNEKE.COM>
Subject: Re: The dreaded AFM adjustment screw
In-Reply-To: <2b9b38180702141153p2d271c80u278716095c32192c@mail.gmail.com>
Content-Type: TEXT/PLAIN; charset=US-ASCII
Is the new AFM new, or rebuilt? I would imagine new ones have the CO screw
set like Dennis said. If not, set it like that, and measure the CO.
Again, the mixture screw doesn't really change O2 reading. You need a CO
tester to really get the AFM screw right.
But, once that is set right, there are many, many other things that can
cause HC and CO. Gasoline in your oil, worn valves, leaky injectors, etc.
I have seen that type of hesistation caused by a bad spark plug or two.
Check/replace wires as well.
What are your compression numbers? That could tell a lot.
Jon
On Wed, 14 Feb 2007, Mike Frost wrote:
> Let me back up a bit here.
>
> First, I am failing smog test for slightly high HC (300) and CO (1.45) so
> that is the impetus for messing with things.
>
> I have done the timing check and tried to adjust idle (with idle stabilizer
> disconnected). I can't get the idle speed down to 920 without killing the
> engine. The idle is stable when the idle stabilizer is connected, except for
> occasional surges up to about 1100 RPM.
>
> The other symptom happens once the engine is up to temperature, at which
> point there is hesitation at the very beginning of the throttle (just past
> the point where the throttle position switch disengages). This hesitation
> can result in the engine dying at intersections. It seems to be worse after
> sitting at idle for a while.
>
> Other than that, there is plenty of power and reasonable gas mileage. I've
> checked for vacuum leaks by spraying stater fluid everywhere.
>
> I checked the voltage from the O2 sensor in open loop and it is hovering
> around 0.84 or so. That is why I decided to adjust the AFM, it seems like
> the mixture at idle is a bit rich. Not to mention the fact that the AFM has
> been swapped and the 'new' one has never been adjusted since it was
> installed.
>
> If you think I am chasing the wrong demon, I am totally open to other ideas.
>
> Mike Frost
> 86 Vanagon GL
>
> On 2/14/07, dhaynes@optonline.net <dhaynes@optonline.net> wrote:
> >
> > The screw actually opens a bypass around the air vane. Clockwise closes
> > the bypass making the mixture slightly richer. Counter clock wise opens it.
> > If the O2 sensor is working properly the adjustment will not make a
> > difference. The bypass is small enough that it only has an effect a idle.
> > Why are you convincing yourself that you need to tamper with it? It it has
> > been tampered with close and open two turns. Then fix what is wrong.
> >
> > Dennis
> >
> > ----- Original Message -----
> > From: Mike Frost
> > Date: Wednesday, February 14, 2007 10:55 am
> > Subject: The dreaded AFM adjustment screw
> > To: vanagon@GERRY.VANAGON.COM
> >
> > > So I have convinced myself that I need to adjust the mixture
> > > screw on the
> > > AFM but I have some trepidation about it. There are two things I
> > > want to
> > > verify before I begin:
> > >
> > > 1. To adjust properly, I disconnect the O2 sensor and measure
> > > it's voltage
> > > at idle, with a target of 0.5VDC.
> > > 2. Turning the screw clockwise will lean the mixture?
> > >
> > > Mike Frost
> > > 86 Vanagon GL
> > >
> >
>
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