Date: Thu, 15 Feb 2007 16:59:04 -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: <2b9b38180702151614l112a64afybe0f5109055e115@mail.gmail.com>
Content-Type: TEXT/PLAIN; charset=US-ASCII
Good work! As a true keyboard mechanic, I agree that it is electrical.
Those grounds will get ya. Look at the ground strap on the right side of
the engine, and go from there. It doesn't hurt to add some extra ground
connections.
One tip on the idle stab. valve: no need to disconnect the vacuum lines.
Simply unplug the electrical connection to the ISV. No muss, no fuss, and
no vacuum leaks.
Good luck,
Jon
On Thu, 15 Feb 2007, Mike Frost wrote:
> It's looking more and more like this is an electrical problem. I will be
> looking at all the grounds related to the O2 and AFM systems.
>
> One thing I discovered was that you can't just pull the hose from the idle
> stabilizer valve, plug it, and leave the end of the valve open. That
> condition effectively creates a huge vacuum leak, and was the reason why I
> couldn't get the idle low enough without killing the engine. Now when I go
> to adjust the idle I pull the hose, put a surgical glove across the mouth of
> the valve, and put the hose back on. This blocks the air flow nicely.
>
> I adjusted the AFM mixture screw and the idle ajdust on the throttle body
> with the above-mentioned air flow block in place. I was able to set the idle
> to 850 and found that the AFM mixture screw was 3 turns from fully CW. I
> experimented with various settings of the AFM mixture screw but the results
> were inconclusive. The readings from the O2 sensor were too erratic. So I
> put the screw back to its original position, installed a monitoring cable so
> I could watch the O2 sensor voltage while driving, and called it a day.
>
> This morning I drove to work with no problems, although I was surprised to
> see the O2 sensor voltage oscillating between zero and some value between
> 0.17VDC and 0.84VDC. It struck me as odd that the voltage should swing
> rhythmically up and down like that when the engine is at a constant speed
> with a constant load. If anyone has an O2 sensor voltage monitor installed,
> you can tell me if that is normal.
>
> Later in the morning I went to drive over to the smog test and there was a
> fairly heavy rain. When I first started out, the O2 sensor voltage was above
> 3.0VDC! The van was running very poorly with hesitation and no power. After
> a few minutes, the voltage reading dropped down into sub-one volt range
> again and the van started running reasonably well again. This is when I
> decided that I have some kind of electrical problem, one that is exacerbated
> by humidity. I have always noticed a stuttering in wet weather, although not
> nearly this bad.
>
> BTW, I still failed the smog test although the HC almost passed this time.
> No significant change to the CO reading. All of this makes perfect sense if
> the ECU is not able to understand what the O2 sensor is trying to tell it.
>
> Mike Frost
> 86 Vanagon GL "WasserLeaker" aka "The Polluter"
>
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