[V8] O2 sensor

Mon Oct 4 14:47:52 EDT 2004

OK.   I misunderstood and thought there was a ground wire in the three
wires connected to the OEM wiring.  It's the sensor's placement in the
exhaust that makes the ground, eh?

At 11:50 AM 10/4/2004 -0600, Ed Kellock wrote:
>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.
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>> >
>> >
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>> 
>> 
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>> Have a V8 answer? ... Please help others by adding to the KB ... all 
>contributions welcome!
>>
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>Have a V8 answer? ... Please help others by adding to the KB ... all 
>contributions welcome!