Date:         Tue, 14 Oct 1997 11:06:31 -0700
Reply-To:     Tom Young <young@SHERLOCK.SIMS.BERKELEY.EDU>
Sender:       Vanagon mailing list <Vanagon@Gerry.SDSC.EDU>
From:         Tom Young <young@SHERLOCK.SIMS.BERKELEY.EDU>
Subject:      Re: O2 mixture questions
Comments: To: db25 <Douglas_M_BENSEN@UMAIL.UMD.EDU>
In-Reply-To:  <199710141738.NAA14788@umailsrv0.umd.edu>
Content-Type: TEXT/PLAIN; charset=US-ASCII

On Tue, 14 Oct 1997, db25 wrote:

> I have several questions when it comes to adjusting my mixture using the
> oxygen sensor.
>         1. Do I have to disconnect the sensor with the engine off?  The
>            computer will have a memory if I don't.  Does it matter?  Can I
>            leave the sensor connected to the computer to read the voltage?

I've always understood that the engine should be off when you disconnect
the O2 sensor.  Since very little seems to be known about Bosch ECU's
inner workings, (at least, I know very little about their inner workings)
I have to answer in a practical fashion; it doesn't seem to matter on my
'81 van.  (The ECU on my '81 is so old, it probably doesn't HAVE any
writtable memory.)

I wouldn't think leaving the sensor connected would make much sense, as
it would be giving feedback to the ECU, and the ECU would try to hold the
mixture at "ideal" by varying the pulse width.  The Bently manual tells
you to disconnect the O2 sensor when setting idle mixture using your CO
sensor (I wish!!)

[snip]

> I realize I have asked a lot of questions, but I don't want to ruin
> anything.  I have a digital meter, but it is very difficult to get a reading
> because of the pulsing.  When the engine is running either rich, or lean,
> the voltage reads steady.  As soon as I get out of the far reaches of the
> scale the pulsing makes reading the voltage difficult.  Any suggestions
> would be appreciated.

I think that's what you're supposed to see.  When I've set my idle
mixture with my DVM I never see a steady voltage around the proper
set-point.  I watch and adjust until the fluctuations hitting above and
below the right voltage seems about even.



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Tom Young               young@sherlock.SIMS.Berkeley.EDU
Lafayette, CA  94549    '81 Vanagon
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