Date: Tue, 4 Jul 2006 16:47:15 -0400
Reply-To: Matt Sutton <msutts@EARTHLINK.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Matt Sutton <msutts@EARTHLINK.NET>
Subject: Re: 88 digifant O2 readings off
In-Reply-To: <6.2.3.4.2.20060704140215.07027cc8@pop1.attglobal.net>
Content-type: text/plain; charset="US-ASCII"
Thanks David!
Super helpful, as your posts always seem to be. As far as marking the AFM
position before fiddling...... well my shame is no longer secret. I know
it's a no-no; my only justification was that with the target open loop O2
sensor voltage being .5 volts, it seemed that the high reading indicated a
wrong setting, and not worth noting. Not much of an excuse, really.
It is back where it started now, more or less. Between the idle adjustment
and the AFM, it seems like there's only a small window where the idle sounds
right, smells right, etc, in open loop mode. I guess I'm still concerned
about the high o2 reading because of the (lucky)correspondence between that
voltage number and CO output. Seems like I'm pushing it as far as passing
emissions goes.
I was reading Dennis Haynes' article on the Type 2 site, and he puts high CO
readings on the doorstep of mixture issues or timing. The timing on mine is
"unknown" at this point, as my timing light got stolen a little while back,
so I'll check that over the weekend I guess.
Thanks again,
Matt
on 7/4/06 2:18 PM, David Beierl at dbeierl@attglobal.net wrote:
> At 12:33 PM 7/4/2006 -0400, Matt Sutton wrote:
>> Temp sensor disconnected after start up
>
> OK, so you're telling the ECU that the engine is ice-cold.
>
>
>> Test Readings at O2 Sensor: -.54v at start
>
> The ECU biases the input with 0.5 volts at some high impedance.
>
>> -after a minute, reading fluctuates but
>> averages .5v
>
> And when the sensor heats up it starts driving the line and swamps
> that fixed signal. The ECU notices and shifts into closed-loop mode
> wherein any time the line is over 500 mv it starts driving the
> mixture lean. As soon as the line falls below 500 mv the ECU starts
> driving it rich again.
>
>> -when temp sensor's disconnected, reading jumps
>> to .9v and pretty much stays there. Very small
>
> but the ECU knows that an ice-cold engine will never run without a
> very rich mixture, so it goes back into open-loop and pours on the
> gasoline. The ECU yells RICH RICH RICH and maybe PTUI! GAS YECCHHH!
>
>> adjustments possible at AFM, but nowhere near
>> where needed to reach the .5v target. There is
>> the some upward movement available, as high as
>> 1.2v.
>>
>> So it's this last result that's troubling me.
>
> Yeah...you oughtn't play tricks on the poor ECU like that, abusing
> its child-like faith in you. <grin> Seriously, it's doing what it's
> supposed to. But I hope you marked where you started with the AFM.
>
>> The van runs fine. And
>> while it misses a little at idle, it always has. I know the 02 sensor's
>> doing it's job, but am worried about leaning too hard on the Cat and ECU to
>> compensate.
>
> I don't know if this is what you're talking about, but on mine you
> can hear the idle shift very slightly as the ECU walks the mixture
> back and forth. If it goes away when you disconnect the O2 sensor,
> that would be it.
>
>
>> Any thoughts?
>
> :-)
> d
>
>
>> Happy 4th,
>>
>> Matt Sutton
>> Brooklyn NY
>> 88GL
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