Date: Wed, 21 Feb 2007 04:41:51 +0000
Reply-To: dhaynes@OPTONLINE.NET
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <dhaynes@OPTONLINE.NET>
Subject: Re: The dreaded AFM adjustment screw
In-Reply-To: <2b9b38180702151614l112a64afybe0f5109055e115@mail.gmail.com>
Content-Type: text/plain; charset=us-ascii
Mike,
I have been traveling, Daytona 500 and Now Disney World so I have not been keeping up with Vanagon E-mails.
Normal O2 sensor operation is to oscillate from .2 to .8 volts. The goal is to average around .5 or so. The fact that you see 3 volts tells me a lot. here is the deal.
Due to rain probably splashing on the sensor, it is cooling and maybe even getting contamination cause it to not only stop producing output, but even becoming an open circuit. Do you at least have the splash-heat shield in place? Yes it matters.
Normally, when the sensor goes open circuit such as when cold, you should see ~.5 to.6 volt on it. This is the bias voltage going to the input of the ECU. Electronic gurus know what i am referring to. You just need to know what should be normal. Since you are seeing voltages way above that, you have at least on bad ground but you may have many.
On many '86 and '87's, there is a ground wire at the base of the oil breather tower. This wire is often in the same harness and the Distributor sensor. The plastic tower makes for a lousy connections. This wire is the 02 sensor reference. Relocate it.
When checking the ground wires, it is not sufficient to check that the rings are in place the wires connected to the terminals, and the screws tight. These wires are corroding and even if still crimped, they may not make a good connection. The corroded copper is almost impossible to solder. My fix has been to replace the terminals with quality terminals with the sealant filled shrink tube on them. Use an anti oxidant to prevent further corrosion and help with conductivity. Sealing the ends is what VW should have done as road dirt and salt gets these connections and can make a real mess.
Dennis
----- Original Message -----
From: Mike Frost
Date: Thursday, February 15, 2007 7:24 pm
Subject: Re: The dreaded AFM adjustment screw
To: vanagon@GERRY.VANAGON.COM
> 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
> exacerbatedby 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"
>
| 
