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Help interpreting oxygen sensor data



 
 
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  #1  
Old June 21st 05, 07:04 AM
Martijn van Duijn
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Default Help interpreting oxygen sensor data

Hi,

After seeing a decrease in mileage on my 96 Ford Taurus wagon (~ 24 to
~20 mpg. 140.000 Mi odo), I decided to take a look at my oxygen sensors
as a possible culprit.
I read out their voltages during idle when warm using my Elm ODB
scantool, and plotted them.

http://www.duijn.info/OxygenSensor.jpg
x in seconds, y in volts

It looks to me that something is fishy in Bank 2, but the signal does
not look like the typical error modes that I read about (sluggish, low,
flat). Bank 1 looks like the examples I saw for good sensors.

I am not experienced enough to make a statement on these curves, but am
hoping they ring a bell with one of you people. Does it look familar, is
my data aquisistion simply too slow (I don't have a scope, sorry...).
The peaks in sensor 2/2 also look like they don't belong there. Is the
fuel injection acting up due to bad info from sensor 1, and too rich a
mixture making its way through the cat? The traces were recorded
separately to improve time resolution...

If a sensor is indeed bad, is it doable to replace it with just basic
tools, or is it best left to a pro?

Thanks for any thoughts you may have.

Martijn
Ads
  #2  
Old June 21st 05, 07:38 AM
Dave Baker
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Posts: n/a
Default


Martijn van Duijn > wrote in message
...
> Hi,
>
> After seeing a decrease in mileage on my 96 Ford Taurus wagon (~ 24 to
> ~20 mpg. 140.000 Mi odo), I decided to take a look at my oxygen sensors
> as a possible culprit.
> I read out their voltages during idle when warm using my Elm ODB
> scantool, and plotted them.
>
> http://www.duijn.info/OxygenSensor.jpg
> x in seconds, y in volts
>
> It looks to me that something is fishy in Bank 2, but the signal does
> not look like the typical error modes that I read about (sluggish, low,
> flat). Bank 1 looks like the examples I saw for good sensors.
>
> I am not experienced enough to make a statement on these curves, but am
> hoping they ring a bell with one of you people. Does it look familar, is
> my data aquisistion simply too slow (I don't have a scope, sorry...).
> The peaks in sensor 2/2 also look like they don't belong there. Is the
> fuel injection acting up due to bad info from sensor 1, and too rich a
> mixture making its way through the cat? The traces were recorded
> separately to improve time resolution...
>
> If a sensor is indeed bad, is it doable to replace it with just basic
> tools, or is it best left to a pro?
>
> Thanks for any thoughts you may have.
>
> Martijn


1/1 appears to be fine. 1/2 should have a relatively flat output though
which appears to indicate that the catalytic converter on that bank isn't
doing much.

2/1 is either dead or genuinely indicating a very weak mixture. However if
the mixture really was very weak then 2/2 wouldn't be displaying higher
readings so it appears that 2/1 really is dead. Until you replace 2/1
there's little point in trying to decide if that converter or 2/2 are ok or
not.

Sensors just unscrew so if you can handle a spanner I very much doubt you
need a 'pro' to do it for you.
--
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)


  #3  
Old June 21st 05, 12:13 PM
MasterBlaster
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Posts: n/a
Default


"Dave Baker" wrote

> > I read out their voltages during idle when warm using my Elm ODB
> > scantool, and plotted them.
> >
> > http://www.duijn.info/OxygenSensor.jpg
> > x in seconds, y in volts


> 1/1 appears to be fine. 1/2 should have a relatively flat output though
> which appears to indicate that the catalytic converter on that bank isn't
> doing much.


1/2 is pretty flat... (it's below 1/1, not beside it).
Of course, that's assuming Martin labelled the charts correctly.

> 2/1 is either dead or genuinely indicating a very weak mixture. However if
> the mixture really was very weak then 2/2 wouldn't be displaying higher
> readings so it appears that 2/1 really is dead. Until you replace 2/1
> there's little point in trying to decide if that converter or 2/2 are ok or
> not.


2/1 (top right) is all over the place, with 2/2 (bottom right) following close behind.

Sticky/plugged injector, misfiring plug, bad wire, vacuum leak?

> Sensors just unscrew so if you can handle a spanner I very much doubt you
> need a 'pro' to do it for you.


Yup.

  #4  
Old June 21st 05, 02:34 PM
aarcuda69062
external usenet poster
 
Posts: n/a
Default

In article <pDSte.73237$on1.52630@clgrps13>,
"MasterBlaster" > wrote:

> "Dave Baker" wrote
>
> > > I read out their voltages during idle when warm using my Elm ODB
> > > scantool, and plotted them.
> > >
> > > http://www.duijn.info/OxygenSensor.jpg
> > > x in seconds, y in volts

>
> > 1/1 appears to be fine. 1/2 should have a relatively flat output though
> > which appears to indicate that the catalytic converter on that bank isn't
> > doing much.

>
> 1/2 is pretty flat... (it's below 1/1, not beside it).
> Of course, that's assuming Martin labelled the charts correctly.


If bank 1 catalytic convertor was storing oxygen properly, what
would/should B1S1 be doing?

> > 2/1 is either dead or genuinely indicating a very weak mixture. However if
> > the mixture really was very weak then 2/2 wouldn't be displaying higher
> > readings so it appears that 2/1 really is dead. Until you replace 2/1
> > there's little point in trying to decide if that converter or 2/2 are ok or
> > not.

>
> 2/1 (top right) is all over the place, with 2/2 (bottom right) following
> close behind.
>
> Sticky/plugged injector, misfiring plug, bad wire, vacuum leak?


Yup, something is amiss.

> > Sensors just unscrew so if you can handle a spanner I very much doubt you
> > need a 'pro' to do it for you.

>
> Yup.


The OP would be wise to scrutinize the fuel trims.
  #5  
Old June 21st 05, 03:37 PM
Dave Baker
external usenet poster
 
Posts: n/a
Default


MasterBlaster > wrote in message
newsDSte.73237$on1.52630@clgrps13...
>
> "Dave Baker" wrote
>
> > > I read out their voltages during idle when warm using my Elm ODB
> > > scantool, and plotted them.
> > >
> > > http://www.duijn.info/OxygenSensor.jpg
> > > x in seconds, y in volts

>
> > 1/1 appears to be fine. 1/2 should have a relatively flat output though
> > which appears to indicate that the catalytic converter on that bank

isn't
> > doing much.

>
> 1/2 is pretty flat... (it's below 1/1, not beside it).
> Of course, that's assuming Martin labelled the charts correctly.


Oops. You're quite right. I read the chart incorrectly. Bank 1 is fine. Bank
2 clearly isn't.

A first step might be to swap sensors 1/1 and 2/1 and see if the rich
readings shown by the second sensor move with the first sensor or stay on
bank 2. If they move to bank 1 then sensor 2/1 (now on bank 1 of course)
needs replacing before anything else can be checked.
--
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)


  #6  
Old June 21st 05, 04:12 PM
Martijn van Duijn
external usenet poster
 
Posts: n/a
Default

aarcuda69062 wrote:
> In article <pDSte.73237$on1.52630@clgrps13>,
> "MasterBlaster" > wrote:
>
>
>>"Dave Baker" wrote
>>
>>
>>>>I read out their voltages during idle when warm using my Elm ODB
>>>>scantool, and plotted them.
>>>>
>>>>http://www.duijn.info/OxygenSensor.jpg
>>>>x in seconds, y in volts

>>
>>
>>
>>>1/1 appears to be fine. 1/2 should have a relatively flat output though
>>>which appears to indicate that the catalytic converter on that bank isn't
>>>doing much.

>>
>>1/2 is pretty flat... (it's below 1/1, not beside it).
>>Of course, that's assuming Martin labelled the charts correctly.

>
>
> If bank 1 catalytic convertor was storing oxygen properly, what
> would/should B1S1 be doing?
>
>
>>>2/1 is either dead or genuinely indicating a very weak mixture. However if
>>>the mixture really was very weak then 2/2 wouldn't be displaying higher
>>>readings so it appears that 2/1 really is dead. Until you replace 2/1
>>>there's little point in trying to decide if that converter or 2/2 are ok or
>>>not.

>>
>>2/1 (top right) is all over the place, with 2/2 (bottom right) following
>>close behind.
>>
>>Sticky/plugged injector, misfiring plug, bad wire, vacuum leak?

>
>
> Yup, something is amiss.
>
>
>>>Sensors just unscrew so if you can handle a spanner I very much doubt you
>>>need a 'pro' to do it for you.

>>
>>Yup.

>
>
> The OP would be wise to scrutinize the fuel trims.


When I recorded the traces, both long terms were -1, short terms
fluctuating a bit between 3 and 9.

Martijn

  #7  
Old June 21st 05, 04:20 PM
Martijn van Duijn
external usenet poster
 
Posts: n/a
Default

MasterBlaster wrote:
> "Dave Baker" wrote
>
>
>>>I read out their voltages during idle when warm using my Elm ODB
>>>scantool, and plotted them.
>>>
>>>http://www.duijn.info/OxygenSensor.jpg
>>>x in seconds, y in volts

>
>
>
>>1/1 appears to be fine. 1/2 should have a relatively flat output though
>>which appears to indicate that the catalytic converter on that bank isn't
>>doing much.

>
>
> 1/2 is pretty flat... (it's below 1/1, not beside it).
> Of course, that's assuming Martin labelled the charts correctly.
>
>
>>2/1 is either dead or genuinely indicating a very weak mixture. However if
>>the mixture really was very weak then 2/2 wouldn't be displaying higher
>>readings so it appears that 2/1 really is dead. Until you replace 2/1
>>there's little point in trying to decide if that converter or 2/2 are ok or
>>not.

>
>
> 2/1 (top right) is all over the place, with 2/2 (bottom right) following close behind.
>
> Sticky/plugged injector, misfiring plug, bad wire, vacuum leak?



Would you guess on of the above are more likely than the sensor itself
being bad?
Easy enough to swap 1 and 2 and try, judging from the other posts.
Platinum plugs and wires are 20.000 miles old, I'd be a bit surprised if
they were bad. Wouldn't vacuum leaks affect both banks equally?
Injector? Perhaps... The engine seems to run OK though. I can try a
cleaner at some point.


Thanks for the comments

Martijn




>
>
>>Sensors just unscrew so if you can handle a spanner I very much doubt you
>>need a 'pro' to do it for you.

>
>
> Yup.
>

  #8  
Old June 21st 05, 08:35 PM
Comboverfish
external usenet poster
 
Posts: n/a
Default



Martijn van Duijn wrote:

> Would you guess on of the above are more likely than the sensor itself
> being bad?
> Easy enough to swap 1 and 2 and try, judging from the other posts.
> Platinum plugs and wires are 20.000 miles old, I'd be a bit surprised if
> they were bad. Wouldn't vacuum leaks affect both banks equally?
> Injector? Perhaps... The engine seems to run OK though. I can try a
> cleaner at some point.


The highly active bank 2 sensor would typically indicate a poor
catalyst on that bank, or an exaust that hasn't reached temperature yet
(not likely since the other side is OK). The bank 1 sensor on that
side shows a less than ideal trace, so you could simply be overloading
that catalyst with excess fuel or air. Since you are using your OBD
data stream to create a graph, your result is a low resolution and
inaccurate (in terms of real time) chart. Note the random pattern of
plot points compared to B1S1.

Anyway, look for something that would cause a mixture issue with one
bank, like pluged EGR ports in the intake, leaking vacuum hose(s)
exiting from a specific runner of the intake, bad injector, wire, etc.
Do you have any cylinder misfire codes? Can your scanner read live
misfire data engine running?

Toyota MDT in MO

  #9  
Old June 21st 05, 08:43 PM
Comboverfish
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Posts: n/a
Default



Martijn van Duijn wrote:

> Platinum plugs and wires are 20.000 miles old, I'd be a bit surprised if
> they were bad. Wouldn't vacuum leaks affect both banks equally?
> Injector? Perhaps... The engine seems to run OK though. I can try a
> cleaner at some point.
>
>
> Thanks for the comments
>
> Martijn


The highly active bank 2 rear sensor would typically indicate a poor
catalyst on that bank, or an exaust that hasn't reached temperature yet

(not likely since the other side is OK). The bank 1 sensor on that
side shows a less than ideal trace, so you could simply be overloading
that catalyst with the incorrect amount of fuel or air. Since you are
using your OBD
data stream to create a graph, your result is a low resolution and
inaccurate (in terms of real time) chart. Note the random pattern of
plot points compared to B1S1.

Anyway, look for something that would cause a mixture issue with one
bank, like pluged EGR ports in the intake, leaking vacuum hose(s)
exiting from a specific runner of the intake, bad injector, wire, etc.
Do you have any cylinder misfire codes? Can your scanner read live
misfire data engine running?


Toyota MDT in MO

  #10  
Old June 21st 05, 08:55 PM
Martijn van Duijn
external usenet poster
 
Posts: n/a
Default

Comboverfish wrote:
>
> Martijn van Duijn wrote:
>
>
>>Would you guess on of the above are more likely than the sensor itself
>>being bad?
>>Easy enough to swap 1 and 2 and try, judging from the other posts.
>>Platinum plugs and wires are 20.000 miles old, I'd be a bit surprised if
>>they were bad. Wouldn't vacuum leaks affect both banks equally?
>>Injector? Perhaps... The engine seems to run OK though. I can try a
>>cleaner at some point.

>
>
> The highly active bank 2 sensor would typically indicate a poor
> catalyst on that bank, or an exaust that hasn't reached temperature yet
> (not likely since the other side is OK). The bank 1 sensor on that
> side shows a less than ideal trace, so you could simply be overloading
> that catalyst with excess fuel or air. Since you are using your OBD
> data stream to create a graph, your result is a low resolution and
> inaccurate (in terms of real time) chart. Note the random pattern of
> plot points compared to B1S1.


Yeah, I noted the erratic curve, my sampling rate is just insufficient
indeed. But I assumed it would normally be similar to bank 1. I am
hoping that excess fuel overloads the cat (would be consistent with poor
mileage), not particularly looking forward to getting a cat replacement.


>
> Anyway, look for something that would cause a mixture issue with one
> bank, like pluged EGR ports in the intake, leaking vacuum hose(s)
> exiting from a specific runner of the intake, bad injector, wire, etc.
> Do you have any cylinder misfire codes? Can your scanner read live
> misfire data engine running?

I'll give it a try this weekend. I'll start by swapping sensors, an
trace the other options as far as I am able to.
No misfire codes, I will have to check on 'live' misfire options. I have
had an EGR code come up (excessive flow detected), but the code comes
randomly and either goes away after 3 drive cycles or I reset it sooner
than that. As the engine runs fine, I blamed the code to a flaky DPFE
sensor that I couldn't be bothered to replace. I think the EGR is common
to both banks though, but not 100% sure on that.

No codes active at this time though.

Martijn



>
> Toyota MDT in MO
>

 




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