At 02:59 PM 8/13/2009, Danny C. wrote:
>cooled vanagon with auto trans). My mechanic tells me to leave the
>oxygen sensor unplugged so that the engine will run cooler. I am
>only getting 15 MPG and was wondering if I plug it in if I will see
>a difference in fuel mileage for the better. Or if having it
>un-plugged is bad. Please share with me the pros and cons of the
>oxygen sensor. Thank you.....

Danny, the sensor is there because the CAT(alytic converter) requires
a very specific mixture to operate properly.  This mixture happens to
fall between the "best power" and the "best economy" mixtures.  In
Europe, where these vehicles were supplied with a CAT, they were also
supplied without an O2 sensor -- that's how I drove mine while it was
in Scotland (when it came over here VWOA installed the CAT and
sensor).  The moral is that *if the engine is in correct running
condition* it will run perfectly well without a sensor, but the
emissions will go up considerably.

If the engine is *not* in correct order then the sensor *may* mask
the problem and in that case the engine will run better with the
sensor than without.

If the sensor itself or its wiring has a problem then the engine will
run worse with the sensor than without.  The sensor commands a
considerable adjustment range of mixture, so if it's jammed rich (or
lean) the ECU will radically alter the mixture in an effort to get
the sensor to respond.

  --
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'89 Po' White Star "Scamp"