I posted a message earlier today about a decrease in mileage after a tuneup
and O2 sensor change. I received a number of replies suggesting that the
problem might be the same as that discussed in an earlier post--inadvertent
grounding of the O2 sensor wire to its coaxial sheath. I think there is a
misunderstanding of this problem which I hope to clarify in this message.

The O2 sensor wire from the ECU is coaxial to protect the signal from
electronic noise that can be induced from the ignition and other sources.
This is a fat green wire that leads to a male spade-lug type connector. This
connector in turn connects to a female connector that's wired to the O2
sensor. The wire from the O2 sensor to the female connector is NOT coaxial.
When you replace the O2 sensor with a generic sensor you reuse the connector
that was on the original sensor. You don't do anything to the connector on
the ECU wire. Thus, this problem is not a concern with normal O2 sensor
replacement. It's only a concern if you are replacing the male connector on
the wire leading to the ECU which you would do only if the connector was
somehow damaged.

ECU --- coaxial wire ---> >--- regular wire --- OXS

Hope this clears this issue up.

Mark McCulley
87 syncro Westfalia