[V8] Oxygen sensor.

[Buchholz, Steven]

... you should be very careful when trying to consider where to connect your
extra ground lead on the 4-wire OXS.  It is very easy to create a ground
loop and end up making things worse than with the factory 3-wire.  When I
did the engine swap on #2 I learned that all of the engine wiring goes
directly through a wiring harness that sits below the throttle linkage at
the back of the engine ... this includes ground wires that go to the ECU.
Let's say you had a situation where the exhaust crossover pipe wasn't well
connected to the engine ground ... now the OXS signal can get altered by the
difference in ground voltage between where you have the OXS grounded and the
actual engine block.  Remember that tenths of a volt can make a difference
in this sort of signal, and when you consider the high ground currents
between the engine block and the body of the car it isn't that hard to
imagine tenths of a volt changes in the ground reference.  Grounding in a
modern car is not as simple as in the old days when all you needed was power
for the starter and lights!

I fully agree that you may well realize an improvement in the OXS' signal to
the ECU by switching to a 4-wire OXS, but you should think carefully about
the grounding.  My recommendation would be to find the ground lugs below the
left distributor and attach the fourth wire to one of the two ground points
there on the back of the engine block.  

Final comment ... I got a non-Bosch 3-wire universal OXS from my BiL's FLAPS
a while back and installed it on #344.  Overall I'd say that it works OK,
but there is a point a couple of minutes after a cold start where the engine
runs poorly for 15 seconds or so ... I suspect this to be due to the ECU
thinking the OXS is warmed up when in fact it has not yet ... I will not
install another OXS in the car that is not made by Bosch and have the same
general design as the standard part ...

Steve B.
San Jose, Kaleefohnia (USA)
> 
> I also use a Ford 4-wire and it works fine. I like the extra 
> ground wire as I 
> think it helps give a more consistent reading and the 
> Motronic seems pretty sensitive to this.
> 
> If you use a 3-wire it is a good idea to make sure the 
> exhaust pipe is well grounded.
>