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

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)

"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.

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.

MasterBlaster > wrote in message
news:pDSte.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)

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

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.
>

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

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

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
>