[V8] O2 sensor

Mon Oct 4 13:51:02 EDT 2004

Yes, the "correct" part is a 3-wire and grounding is provided through
the sensor to the exhaust system.

The extra wire of the 4-wire sensor provides an "external" ground. 
This is attractive because of the age of these cars and the
corresponding condition of the exhaust systems.  The 4th wire provides
a surer ground when there's any doubt.

Ed

On Mon, 04 Oct 2004 12:56:46 -0400, Kneale Brownson
<knotnook at traverse.com> wrote:
> So the V8 OEM sensor is a three-wire, isn't it?  Where does the original
> wiring ground the O2 sensor?
> 
> 
> 
> At 08:57 AM 10/4/2004 -0600, dsaad at icehouse.net wrote:
> >The O2 sensor is "analog". It generates a very small voltage from zero to
> >around
> >1 volt based on oxygen content. Normal operating voltage for a proper
> >mixture is
> >about 0.7 volts.
> >If there is a difference in the ground reference voltage between the ECU and
> >the
> >engine block then this voltage adds algebraically to the actual generated
> >voltage - thus offsetting it. This offset voltage can really cause problems
> >because the sensor output voltage is not linear - it is exponential - so a
> >small
> >voltage change can mean a big mixture change by the ECU. If the ground
> >reference
> >changes - as it could by normal engine movement and vibration on a one or
> three
> >wire setup (think rusty exhaust pipes/bolts, etc) then the ECU will never be
> >able to stabilize mixture.
> >The software in many ECUs can detect this and make allowances but our
> >vintage of
> >Bosch software (I think version 1.2) does not do this. Any little thing out of
> >whack causes the ECU to overcorrect too quickly and that shows up as "the
> >surge".
> >The O2 sensor also "ages" meaning that over time it responds more slowly to
> >mixture changes. This can also be compensated for by more clever software.
> >
> >The O2 is not the only sensor that can do this either. The MAF, engine temp,
> >and
> >air temp are all also susceptible.
> >
> >On the V8, the engine speed and crank reference are analog as well (I think
> >they
> >come under the magnetic reluctance catagory) however they are converted from a
> >sine wave into digital pulses before being processed by the ECU. A voltage
> >offset here can cause very wierd problems - like engines that will not run
> over
> >2000 RPM.
> >btw, the brake wheel sensors are the same type as engine speed.
> >
> >The cam position sensor on the right head is a digital type sensor. It
> >outputs a
> >5 volt digital (square wave) pulse so no conversion needs to be done by the
> >ECU.
> >
> >
> >Guess I should get to work now... but this is more fun :-)
> >
> >
> >Dave
> >
> >
> >Quoting Tony and Lillie <tonyandlillie1 at earthlink.net>:
> >
> >> I'm not saying the fourt was disconnected ever, rather, I switched mine and
> >> Zay's cars to 4-wire using the auxilary fan ground on the drivers strut
> >> tower as the ground for the fourth wire (gray). This cured the "surging" the
> >> cars both did (mine was worse). My question is why the different grounds
> >> would give diffierent signals. Also, where the ECU sees the reference to be,
> >> and how an O2 sensor works.
> >>
> >> Tony
> >> ----- Original Message -----
> >> From: "Buchholz, Steven" <Steven.Buchholz at kla-tencor.com>
> >> To: <v8 at audifans.com>
> >> Sent: Friday, October 01, 2004 7:18 PM
> >> Subject: RE: [V8] O2 sensor
> >>
> >>
> >> ... well, if you don't have the fourth wire connected to anything it is
> >> as if there is an open circuit ... I'd expect the ECU would generate
> >> codes to this effect ... but yes, I'd expect your car to run like crap
> >> this way!
> >>
> >> Connecting the fourth wire to *any* ground is better than *no* ground
> >> ... as was pointed out, one of the OXS heater leads is in fact grounded
> >> ... this would not be a terrible place to attach the ground wire ... be
> >> extra careful to determine which pin is grounded because the other gets
> >> power when the engine is running ... this would probably be a bad thing
> >> for the ECU to see as a reference and might well damage the ECU.  This
> >> also fits with the esthetics of building an adapter for the Ford sensor
> >> ... the 4-3 wire adapter would then be self contained.
> >>
> >> Steve B
> >> San Jose, CA (USA)
> >> >
> >> > It is an interesting theory, where to ground the fourth wire.
> >> > I'm going to
> >> > get out the MM and check the voltage drop from the block to
> >> > the fan ground
> >> > (in my free time, of course :-) ). However, the car runs
> >> > about 100% better
> >> > since I put the 4 wire in, and Zay has reported the same for
> >> > his car. Both
> >> > use the fan ground for the fourth wire.
> >> >
> >> > Can anyone explain the theory of why the engine would be
> >> > better if there is
> >> > a voltage drop. The O2 sensor is not connected to the engine,
> >> > but rather the
> >> > ECU, so I don't see the difference anyhow. BUT, if one of you
> >> > can educate
> >> > me, I'd be happy to hear how it works.
> >> _______________________________________________
> >> 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!
> >>
> >> _______________________________________________
> >> 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!
> >>
> >
> >
> >
> >_______________________________________________
> >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!
> 
> 
> 
> _______________________________________________
> 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!
>