[V8] O2 sensor

Mon Oct 4 12:57:07 EDT 2004

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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