OBD-II: testing cat for NOx adsorption

I know the ECM tests the cat's oxidation-side for O2 storage by
1) commanding rich for 5 seconds to drain the cat of O2, then
2) commanding lean for 5 seconds to load the cat with O2 while
3) counting the time that passes before the secondary HO2S flips.

But how does it test for proper NO (NOx) handling?

The reduction side adsorbs and splits NO into N (releasing the O), joining
the adsorbed Ns together into N2s and then releasing them, but what's the
sequence that tells the ECM that this is occurring in a compliant manner?

--
Tegger

In article >,
Tegger > wrote:

> I know the ECM tests the cat's oxidation-side for O2 storage by
> 1) commanding rich for 5 seconds to drain the cat of O2, then
> 2) commanding lean for 5 seconds to load the cat with O2 while
> 3) counting the time that passes before the secondary HO2S flips.

That hasn't been my observation, but maybe possible that a few
manufacturers that I'm not familiar with have adopted that strategy...

> But how does it test for proper NO (NOx) handling?

The same way it tests for proper HC and CO handling.

> The reduction side

There is no reduction "side." The oxidation and reduction processes
occur at the same place, same time on the noble metals within the
cat-con. Some of these metals are more efficient at NOx reduction, some
are more efficient at HC/CO oxidation but they all participate in the
process. A loss in efficiency treating one pollutant will result in a
loss of efficiency in the other two.

> adsorbs and splits NO into N (releasing the O), joining
> the adsorbed Ns together into N2s and then releasing them, but what's the
> sequence that tells the ECM that this is occurring in a compliant manner?

aarcuda69062 > wrote in
news:nonelson-A83C49.22013905112010@reserved-multicast-range-NOT-delegate
d.example.com:

> In article >,
> Tegger > wrote:
>
>> I know the ECM tests the cat's oxidation-side for O2 storage by
>> 1) commanding rich for 5 seconds to drain the cat of O2, then
>> 2) commanding lean for 5 seconds to load the cat with O2 while
>> 3) counting the time that passes before the secondary HO2S flips.
>
> That hasn't been my observation, but maybe possible that a few
> manufacturers that I'm not familiar with have adopted that strategy...



A training document I have says that's how Honda does it.

My concern has specifically do with an OBD-II Honda, but I had the
(evidently erroneous) idea that the general processes were the same across
automakers.


>
>> But how does it test for proper NO (NOx) handling?
>
> The same way it tests for proper HC and CO handling.



Do you mind giving me a quick overview of what your observations are
regarding this?

I'm particularly interested in how the ECM uses the secondary O2 sensor to
tell the difference between HC/CO and NO handling.




>
>> The reduction side
>
> There is no reduction "side." The oxidation and reduction processes
> occur at the same place, same time on the noble metals within the
> cat-con.



Thank you. I didn't know that.


--
Tegger

On 11/05/2010 05:34 PM, Tegger wrote:
> I know the ECM tests the cat's oxidation-side for O2 storage by
> 1) commanding rich for 5 seconds to drain the cat of O2, then
> 2) commanding lean for 5 seconds to load the cat with O2 while
> 3) counting the time that passes before the secondary HO2S flips.
>
> But how does it test for proper NO (NOx) handling?
>
> The reduction side adsorbs and splits NO into N (releasing the O), joining
> the adsorbed Ns together into N2s and then releasing them, but what's the
> sequence that tells the ECM that this is occurring in a compliant manner?

absent an "N" sensor, and i'm not aware of any vehicles that have such a
thing, it just, as you say, reads the time the cat takes to flip from
one oxygen state to the other, and using prior lab testing, maps
secondary Oâ‚‚ against known NOx output conversion efficiency. once
measured out of the mapped range, it has to presume the cat's NOx
conversion is bad.


--
nomina rutrum rutrum

On 11/06/2010 06:01 AM, Tegger wrote:
> > wrote in
> news:nonelson-A83C49.22013905112010@reserved-multicast-range-NOT-delegate
> d.example.com:
>
>> In >,
>> > wrote:
>>
>>> I know the ECM tests the cat's oxidation-side for O2 storage by
>>> 1) commanding rich for 5 seconds to drain the cat of O2, then
>>> 2) commanding lean for 5 seconds to load the cat with O2 while
>>> 3) counting the time that passes before the secondary HO2S flips.
>>
>> That hasn't been my observation, but maybe possible that a few
>> manufacturers that I'm not familiar with have adopted that strategy...
>
>
>
> A training document I have says that's how Honda does it.
>
> My concern has specifically do with an OBD-II Honda, but I had the
> (evidently erroneous) idea that the general processes were the same across
> automakers.
>
>
>>
>>> But how does it test for proper NO (NOx) handling?
>>
>> The same way it tests for proper HC and CO handling.
>
>
>
> Do you mind giving me a quick overview of what your observations are
> regarding this?
>
> I'm particularly interested in how the ECM uses the secondary O2 sensor to
> tell the difference between HC/CO and NO handling.

it doesn't and it can't - it's an oxygen sensor. however, the efficacy
of the cat's carbon and nitrogen catalysis go hand in hand, so if one
end is degrading, the other is presumed to be degrading too.


>
>
>
>
>>
>>> The reduction side
>>
>> There is no reduction "side." The oxidation and reduction processes
>> occur at the same place, same time on the noble metals within the
>> cat-con.
>
>
>
> Thank you. I didn't know that.

hopefully because it's not correct. there are two different honeycombs
in the modern cat. first one [engine end] deals with carbon. the
second, [tailpipe end] deals with nitrogen. the metal mixes on the
ceramic matrix at each end are slightly different.

http://www.ridelust.com/wp-content/u...cconverter.jpg


--
nomina rutrum rutrum

In article >,
Tegger > wrote:

> aarcuda69062 > wrote in
> news:nonelson-A83C49.22013905112010@reserved-multicast-range-NOT-delegate
> d.example.com:
>
> > In article >,
> > Tegger > wrote:
> >
> >> I know the ECM tests the cat's oxidation-side for O2 storage by
> >> 1) commanding rich for 5 seconds to drain the cat of O2, then
> >> 2) commanding lean for 5 seconds to load the cat with O2 while
> >> 3) counting the time that passes before the secondary HO2S flips.
> >
> > That hasn't been my observation, but maybe possible that a few
> > manufacturers that I'm not familiar with have adopted that strategy...
>
>
>
> A training document I have says that's how Honda does it.
>
> My concern has specifically do with an OBD-II Honda, but I had the
> (evidently erroneous) idea that the general processes were the same across
> automakers.

I won't dispute that the injector pulse width alternates between
slightly lean and slightly rich, the 5 second interval though does not
jive with conventional wisdom or what can be observed when one views O2
sensor activity on a lab scope and injector on time on a lab scope via a
low amps probe.

>
> >
> >> But how does it test for proper NO (NOx) handling?
> >
> > The same way it tests for proper HC and CO handling.
>
>
>
> Do you mind giving me a quick overview of what your observations are
> regarding this?

The best opportunity is right after you replace a catalytic converter
using OEM parts. First step is making sure the PCM has proper fuel
control including proper airflow measurement. Test drive the vehicle
under varied operating conditions, typically the upstream O2s will be
cycling during idle and cruise. The down stream O2s will be outputing
near 900mv and you may see the occasional swing to low voltage as the
cat burps off O2 as the cat-con becomes saturated.

> I'm particularly interested in how the ECM uses the secondary O2 sensor to
> tell the difference between HC/CO and NO handling.

It wouldn't necessarily see a difference such that it would specifically
identify NOx exceeding the FTP threshold, NOx, CO and HC treatment are
all part of the same catalytic process. As that process degrades the
downstream O2 sensor output begins to mimic the upstream O2 sensor
output.

This may all change in the future if and when the OEMs begin using
dedicated NOx sensors in the exhaust stream. Prepare for some
astronomical sensor prices when that happens...

>
>
>
> >
> >> The reduction side
> >
> > There is no reduction "side." The oxidation and reduction processes
> > occur at the same place, same time on the noble metals within the
> > cat-con.
>
>
>
> Thank you. I didn't know that.

On 11/06/2010 07:58 AM, aarcuda69062 wrote:
> In >,
> > wrote:
>
>> > wrote in
>> news:nonelson-A83C49.22013905112010@reserved-multicast-range-NOT-delegate
>> d.example.com:
>>
>>> In >,
>>> > wrote:
>>>
>>>> I know the ECM tests the cat's oxidation-side for O2 storage by
>>>> 1) commanding rich for 5 seconds to drain the cat of O2, then
>>>> 2) commanding lean for 5 seconds to load the cat with O2 while
>>>> 3) counting the time that passes before the secondary HO2S flips.
>>>
>>> That hasn't been my observation, but maybe possible that a few
>>> manufacturers that I'm not familiar with have adopted that strategy...
>>
>>
>>
>> A training document I have says that's how Honda does it.
>>
>> My concern has specifically do with an OBD-II Honda, but I had the
>> (evidently erroneous) idea that the general processes were the same across
>> automakers.
>
> I won't dispute that the injector pulse width alternates between
> slightly lean and slightly rich, the 5 second interval though does not
> jive with conventional wisdom or what can be observed when one views O2
> sensor activity on a lab scope and injector on time on a lab scope via a
> low amps probe.

translation: it's typically faster than 5 seconds.


>
>>
>>>
>>>> But how does it test for proper NO (NOx) handling?
>>>
>>> The same way it tests for proper HC and CO handling.
>>
>>
>>
>> Do you mind giving me a quick overview of what your observations are
>> regarding this?
>
> The best opportunity is right after you replace a catalytic converter
> using OEM parts. First step is making sure the PCM has proper fuel
> control including proper airflow measurement. Test drive the vehicle
> under varied operating conditions, typically the upstream O2s will be
> cycling during idle and cruise. The down stream O2s will be outputing
> near 900mv and you may see the occasional swing to low voltage as the
> cat burps off O2 as the cat-con becomes saturated.
>
>> I'm particularly interested in how the ECM uses the secondary O2 sensor to
>> tell the difference between HC/CO and NO handling.
>
> It wouldn't necessarily see a difference such that it would specifically
> identify NOx exceeding the FTP threshold, NOx, CO and HC treatment are
> all part of the same catalytic process.

no, they're separate processes. there are typically two separate
matricies on a modern catalytic converter - platinum/palladium on the
[front] carbon end, platinum/rhodium on the [rear] nitrogen end.

again: http://www.ridelust.com/wp-content/u...cconverter.jpg


> As that process degrades the
> downstream O2 sensor output begins to mimic the upstream O2 sensor
> output.
>
> This may all change in the future if and when the OEMs begin using
> dedicated NOx sensors in the exhaust stream. Prepare for some
> astronomical sensor prices when that happens...

let us know when anyone starts using nitrogen sensors...


>
>>
>>
>>
>>>
>>>> The reduction side
>>>
>>> There is no reduction "side." The oxidation and reduction processes
>>> occur at the same place, same time on the noble metals within the
>>> cat-con.
>>
>>
>>
>> Thank you. I didn't know that.


--
nomina rutrum rutrum

In article > ,
jim beam > wrote:

> On 11/06/2010 06:01 AM, Tegger wrote:
> > > wrote in
> > news:nonelson-A83C49.22013905112010@reserved-multicast-range-NOT-delegate
> > d.example.com:
> >
> >> In >,
> >> > wrote:
> >>
> >>> I know the ECM tests the cat's oxidation-side for O2 storage by
> >>> 1) commanding rich for 5 seconds to drain the cat of O2, then
> >>> 2) commanding lean for 5 seconds to load the cat with O2 while
> >>> 3) counting the time that passes before the secondary HO2S flips.
> >>
> >> That hasn't been my observation, but maybe possible that a few
> >> manufacturers that I'm not familiar with have adopted that strategy...
> >
> >
> >
> > A training document I have says that's how Honda does it.
> >
> > My concern has specifically do with an OBD-II Honda, but I had the
> > (evidently erroneous) idea that the general processes were the same across
> > automakers.
> >
> >
> >>
> >>> But how does it test for proper NO (NOx) handling?
> >>
> >> The same way it tests for proper HC and CO handling.
> >
> >
> >
> > Do you mind giving me a quick overview of what your observations are
> > regarding this?
> >
> > I'm particularly interested in how the ECM uses the secondary O2 sensor to
> > tell the difference between HC/CO and NO handling.
>
> it doesn't and it can't - it's an oxygen sensor. however, the efficacy
> of the cat's carbon and nitrogen catalysis go hand in hand, so if one
> end is degrading, the other is presumed to be degrading too.
>
>
> >
> >
> >
> >
> >>
> >>> The reduction side
> >>
> >> There is no reduction "side." The oxidation and reduction processes
> >> occur at the same place, same time on the noble metals within the
> >> cat-con.
> >
> >
> >
> > Thank you. I didn't know that.
>
> hopefully because it's not correct. there are two different honeycombs
> in the modern cat. ^^^^^^

That may have been the design back in the 80s, it isn't how it's done
now. There may be two ceramic bricks but they contain the same metals
and function the same way.

> first one [engine end] deals with carbon. the
> second, [tailpipe end] deals with nitrogen.

Not only is that statement backwards, it makes no sense.
If the "tailpipe end" of the cat is the NOx reduction part, it wouldn't
be able to contribute oxygen molecules to assist the oxidation of HC and
CO.

But let's go back to the 80s when they did use an air tap into the
cat-con, that tap was typically placed in the center of the cat-con,
does it make sense that a NOx reduction could be accomplished using the
addition of Nitrogen as part of the process?

> the metal mixes on the
> ceramic matrix at each end are slightly different.

Yup, that's the way GM did it back in 1982.

> http://www.ridelust.com/wp-content/u...cconverter.jpg

There is a lot of erroneous information out there and an awful lot that
has been taught wrong, even by the OEMs.

In article > ,
jim beam > wrote:

> On 11/06/2010 07:58 AM, aarcuda69062 wrote:
> > In >,
> > > wrote:
> >
> >> > wrote in
> >> news:nonelson-A83C49.22013905112010@reserved-multicast-range-NOT-delegate
> >> d.example.com:
> >>
> >>> In >,
> >>> > wrote:
> >>>
> >>>> I know the ECM tests the cat's oxidation-side for O2 storage by
> >>>> 1) commanding rich for 5 seconds to drain the cat of O2, then
> >>>> 2) commanding lean for 5 seconds to load the cat with O2 while
> >>>> 3) counting the time that passes before the secondary HO2S flips.
> >>>
> >>> That hasn't been my observation, but maybe possible that a few
> >>> manufacturers that I'm not familiar with have adopted that strategy...
> >>
> >>
> >>
> >> A training document I have says that's how Honda does it.
> >>
> >> My concern has specifically do with an OBD-II Honda, but I had the
> >> (evidently erroneous) idea that the general processes were the same across
> >> automakers.
> >
> > I won't dispute that the injector pulse width alternates between
> > slightly lean and slightly rich, the 5 second interval though does not
> > jive with conventional wisdom or what can be observed when one views O2
> > sensor activity on a lab scope and injector on time on a lab scope via a
> > low amps probe.
>
> translation: it's typically faster than 5 seconds.

But Teggers' training document says 5 seconds. Are you suggesting that
there may be some bad information being offered Jim?

>
> >
> >>
> >>>
> >>>> But how does it test for proper NO (NOx) handling?
> >>>
> >>> The same way it tests for proper HC and CO handling.
> >>
> >>
> >>
> >> Do you mind giving me a quick overview of what your observations are
> >> regarding this?
> >
> > The best opportunity is right after you replace a catalytic converter
> > using OEM parts. First step is making sure the PCM has proper fuel
> > control including proper airflow measurement. Test drive the vehicle
> > under varied operating conditions, typically the upstream O2s will be
> > cycling during idle and cruise. The down stream O2s will be outputing
> > near 900mv and you may see the occasional swing to low voltage as the
> > cat burps off O2 as the cat-con becomes saturated.
> >
> >> I'm particularly interested in how the ECM uses the secondary O2 sensor to
> >> tell the difference between HC/CO and NO handling.
> >
> > It wouldn't necessarily see a difference such that it would specifically
> > identify NOx exceeding the FTP threshold, NOx, CO and HC treatment are
> > all part of the same catalytic process.
>
> no, they're separate processes. there are typically two separate
> matricies on a modern catalytic converter - platinum/palladium on the
> [front] carbon end, platinum/rhodium on the [rear] nitrogen end.
>
> again: http://www.ridelust.com/wp-content/u...cconverter.jpg

Again: 1980s watered down wisdom not to mention backwards.

>
> > As that process degrades the
> > downstream O2 sensor output begins to mimic the upstream O2 sensor
> > output.
> >
> > This may all change in the future if and when the OEMs begin using
> > dedicated NOx sensors in the exhaust stream. Prepare for some
> > astronomical sensor prices when that happens...
>
> let us know when anyone starts using nitrogen sensors...

I will.

On 11/06/2010 08:30 AM, aarcuda69062 wrote:
> In article<ZIednWtSc6Jc9UjRnZ2dnUVZ_vkAAAAA@speakeasy .net>,
> jim > wrote:
>
>> On 11/06/2010 06:01 AM, Tegger wrote:
>>> > wrote in
>>> news:nonelson-A83C49.22013905112010@reserved-multicast-range-NOT-delegate
>>> d.example.com:
>>>
>>>> In >,
>>>> > wrote:
>>>>
>>>>> I know the ECM tests the cat's oxidation-side for O2 storage by
>>>>> 1) commanding rich for 5 seconds to drain the cat of O2, then
>>>>> 2) commanding lean for 5 seconds to load the cat with O2 while
>>>>> 3) counting the time that passes before the secondary HO2S flips.
>>>>
>>>> That hasn't been my observation, but maybe possible that a few
>>>> manufacturers that I'm not familiar with have adopted that strategy...
>>>
>>>
>>>
>>> A training document I have says that's how Honda does it.
>>>
>>> My concern has specifically do with an OBD-II Honda, but I had the
>>> (evidently erroneous) idea that the general processes were the same across
>>> automakers.
>>>
>>>
>>>>
>>>>> But how does it test for proper NO (NOx) handling?
>>>>
>>>> The same way it tests for proper HC and CO handling.
>>>
>>>
>>>
>>> Do you mind giving me a quick overview of what your observations are
>>> regarding this?
>>>
>>> I'm particularly interested in how the ECM uses the secondary O2 sensor to
>>> tell the difference between HC/CO and NO handling.
>>
>> it doesn't and it can't - it's an oxygen sensor. however, the efficacy
>> of the cat's carbon and nitrogen catalysis go hand in hand, so if one
>> end is degrading, the other is presumed to be degrading too.
>>
>>
>>>
>>>
>>>
>>>
>>>>
>>>>> The reduction side
>>>>
>>>> There is no reduction "side." The oxidation and reduction processes
>>>> occur at the same place, same time on the noble metals within the
>>>> cat-con.
>>>
>>>
>>>
>>> Thank you. I didn't know that.
>>
>> hopefully because it's not correct. there are two different honeycombs
>> in the modern cat. ^^^^^^
>
> That may have been the design back in the 80s, it isn't how it's done
> now. There may be two ceramic bricks but they contain the same metals
> and function the same way.

untrue.

http://en.wikipedia.org/wiki/Rhodium#Catalyst
http://en.wikipedia.org/wiki/Palladium#Catalysis

catalysis occurs at different temperatures too - that's why people are
taught too use an i.r. thermometer on a cat to see if it's working
correctly.

i'm not giving you a hard time - it's just that a lot of car tech
teaching and information on this subject is "black box" - you don't
/need/ to know what's really going on inside, and most people don't know
anyway.


>
>> first one [engine end] deals with carbon. the
>> second, [tailpipe end] deals with nitrogen.
>
> Not only is that statement backwards, it makes no sense.
> If the "tailpipe end" of the cat is the NOx reduction part, it wouldn't
> be able to contribute oxygen molecules to assist the oxidation of HC and
> CO.

see above. you need oxyhen to reduce CO to COâ‚‚. NOx you can just split
- per the wiki link.


>
> But let's go back to the 80s when they did use an air tap into the
> cat-con, that tap was typically placed in the center of the cat-con,
> does it make sense that a NOx reduction could be accomplished using the
> addition of Nitrogen as part of the process?

good point, but what i understand is that in modern fuel injection
systems, there is sufficient oxygen in the exhaust stream to oxidize the
carbon/hydrocarbon content, so that's done first to raise temperatures
that allow the nitrogen conversion to happen efficiently. you don't
want to re-heat Nâ‚‚ and Oâ‚‚ or you'd get NOx again.


>
>> the metal mixes on the
>> ceramic matrix at each end are slightly different.
>
> Yup, that's the way GM did it back in 1982.
>
>> http://www.ridelust.com/wp-content/u...cconverter.jpg
>
> There is a lot of erroneous information out there and an awful lot that
> has been taught wrong, even by the OEMs.

true dat!

--
nomina rutrum rutrum