Date:         Wed, 15 Oct 1997 10:54:25 -0500
Reply-To:     "Rick Sherrod (hopeless VW nut)" <kdf_cars@MYLINK.NET>
Sender:       Vanagon mailing list <Vanagon@Gerry.SDSC.EDU>
From:         "Rick Sherrod (hopeless VW nut)" <kdf_cars@MYLINK.NET>
Organization: Specialty Automotive
Subject:      Re: 02 mixture questions
Content-Type: text/plain; charset=us-ascii

>>>rom:    db25 <Douglas_M_BENSEN@UMAIL.UMD.EDU>
Subject: O2 mixture questions

>>>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?

   >>>     2. Can I use an analog volt meter to better see the voltage sweeps?
           I was afraid internal resistance of the volt meter would cause
           problems.

>>>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.

>>>Thanks,
Doug
>>>'86 GL Westy

Doug,

You should be able to set your mixture just fine while connecting/disconnecting 02 sensor
while engine is running.    I recommend testing to see if the mixture needs adjusting first,
though.

RICH TEST:
Attach your DIGITAL multimeter to 02 sensor (still connected to harness green wire),
should read between .4 & .7 volts or so engine warmed up and idling.  remove vacuum hose
from fuel pressure regulator & hold finger over vacuum leak (hose end).  Did the reading
change?   If the reading changes and stays changed, you are out of adjustment and your
computer can't compensate.  Reconnect hose to regulator & try next test.  Adjust
mixture if out of adjustment.

LEAN TEST:
Multimeter still in place as with rich test and engine running, remove oil filler cap.  Did the
reading change?  If the reading changes and stays changed, you are out of adjustment
and your computer can't compensate.  Adjust mixture if out of adjustment.

02 SENSOR TEST:
If 02 output remains the same during the previous tests then either the mixture
adjustment is within specs, or your 02 sensor is shorted in one fixed spot and is not
reporting to the computer what it should.  The easiest way to check is:
While mutimeter still hooked up (to 02 sensor black wire), disconnect the 02 sensor from
the harness green wire and read the 02 sensor output without the computer adjusting
mixture.  Perform Rich & Lean tests again.  if this time the tests should have a definite
effect on the readings, your 02 sensor seems to be reporting.  This is the time that most
will adjust the fuel mixture to the .5 volts or so just for G.P.  I prefer not to if the first
Rich & Lean tests are in specs and the vehicle runs well & gets good fuel mileage.  There's
not much point then, because the computer is in control.

Questions/comments?
Rick Sherrod
Macon,GA
'82 Vanagon mutt V-6 (soon to be on the road)