Date:         Tue, 4 Jul 2006 14:18:55 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: 88 digifant O2 readings off
Comments: To: Matt Sutton <msutts@EARTHLINK.NET>
In-Reply-To:  <C0D01090.65BE%msutts@earthlink.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed

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

--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage," '85 GL "Poor Relation"