Date: Thu, 15 Feb 2007 16:14:04 -0800
Reply-To: Mike Frost <wasserleaker@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mike Frost <wasserleaker@GMAIL.COM>
Subject: Re: The dreaded AFM adjustment screw
In-Reply-To: <45D3A296.9050603@telus.net>
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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"