[V8] O2 sensor

[dsaad at icehouse.net]

I agree about the need for a good ground for the 4-wire sensor. I chose to use
the ground wire (one of the white wires) that goes to the sensor heater. It
seems to work fine for me, it is easy to get to, and it probably terminates at
or in the ECU. There could be some voltage drop on this wire - that would show
up as an offset as Steve pointed out, but it worked fine for me. Having the
ground terminate in the ECU is the whole point of the 4-wire setup.
If you are going to go with this sensor permenantly then get the mating plug
either new from a ford dealer or a junk yard. I made an adaptor for my car that
will accept either the 3-wire or 4-wire so I could easily use either.
No vehicle side wires were cut on my car. Something I always try to do so I can
always get back to original if I want to.

Dave


Quoting "Buchholz, Steven" <Steven.Buchholz at kla-tencor.com>:

> ... IMO you've got to be a bit more careful than this with grounds ...
>
> The ground wire provides the reference for the OXS signal ... you have
> to be careful not to bias the signal because it will cause the ECU to
> get an improper evaluation of the state of the car.  There are actually
> two ground points on the back of the engine block below the left
> distributor.  I heartily recommend that if you are doing the 4-wire
> conversion that you connect as close as possible to one of these to
> ensure the signal the ECU signal sees is the one the OXS is generating.
>
>
> To be a bit more detailed about my concerns with the attachment to the
> body of the car ... there can easily be a voltage drop between the
> engine block and the frame of the car in the hundreds of millivolts.
> Furthermore this voltage drop will vary depending upon what loads are
> being placed on the electrical system ... coolant fan, head lights ...
> even a discharged battery ... and if you attach the ground of the OXS to
> the body of the car you will automatically apply this voltage offset to
> the signals the ECU is reading for the OXS input.  In addition to this
> offset, the long ground path can allow higher frequency noise to get
> coupled into the OXS signal.  You may end up with a car that runs well
> in the day time but misbehaves at night.  Believe me, ground induced
> issues can be a PITA to isolate and resolve ...
>
> Steve B
> San Jose, CA (USA)
> >
> > The gray wire is the extra, it needs to go to the other
> > ground. I ran mine
> > to the ground for the aux fan on the drivers shock tower. If you are
> > planning on keeping this car, I'd also recommend getting the
> > plug from a
> > Ford. Any of the 4.6 cars use four of them, so it shouldn't
> > be hard to find
> > one. The colors aren't the same on the plug, but just line them up by
> > position, and connect like wires. The two whites are the
> > same, so they can
> > go to either corresponding white. same for the black wire.
> _______________________________________________
> Audifans V8 mailing list
> Send posts to: mailto:V8 at audifans.com
> Manage your list connection: http://www.audifans.com/mailman/listinfo/v8
> Have an Audi V8 question?  Check the Audifans Knowledgebase!
> http://www.audi-quattro.org/cgi-bin/twiki/view/Audi/V8
> Have a V8 answer? ... Please help others by adding to the KB ... all
> contributions welcome!
>