[V8] Oxygen sensor ground wire attachment point

[Ed Kellock]

Steve, after reading your email, I decided to relocate my OXS ground wire.  I found a bolt that goes into the block about where you suggested.  It's right behind the bracket for the cruise control and throttle linkage.  There was only one wire attached to it.  I loosened it, sprayed with carb cleaner then brake cleaner (because I'm out of electrical contact cleaner) and added the OXS ground wire to it.

The results are confusing.  The surging seems to be much less now.  But there are other results that I didn't expect and don't necessarily understand.

Before, cold starts were terrible.  It would crank fire and die, then fire right back up but bog until it warmed some.  now that is gone.  

Before, with light throttle application at around 1500 rpm, it would sometimes buck or miss just a once or twice.  Now this is much more pronounced, especially when the car is partially warm.  

When fully warm, which is reletive here now with the cold weather, the surging is nearly gone.  I'm thinking it may go away entirely as the ECU learns.  Actually, I think I'll pull fuse #27 before I leave work today to clear the ecu adaptive memory.

I didn't expect any change to the cold start behavior because the system is open loop then right?

I'm wondering if the carb/brake cleaner had an effect on something else that might be below the ground bolt.  Are the timing and ref sensors near there?  

Kinda weird stuff, but so far, for the better overall.

Confounded in Colorado Springs

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From: "Buchholz, Steven" <Steven.Buchholz at kla-tencor.com>
Date: 2004/01/30 Fri AM 11:04:42 MST

... 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)