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?
That hasn't been my observation, but maybe possible that a few manufacturers that I'm not familiar with have adopted that strategy...
The same way it tests for proper HC and CO handling.
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.
aarcuda69062 wrote in news:nonelson-A83C49.22013905112010@reserved-multicast-range-NOT-delegate d.example.com:
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.
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.
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 O? against known NOx output conversion efficiency. once measured out of the mapped range, it has to presume the cat's NOx conversion is bad.
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.
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.
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.
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.
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...
translation: it's typically faster than 5 seconds.
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:
formatting link
let us know when anyone starts using nitrogen sensors...
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.
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?
Yup, that's the way GM did it back in 1982.
There is a lot of erroneous information out there and an awful lot that has been taught wrong, even by the OEMs.
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.
see above. you need oxyhen to reduce CO to CO?. NOx you can just split
- per the wiki link.
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 N? and O? or you'd get NOx again.
yup. and it wouldn't be the first time in the automotive world. but it might be the maximum interval also. i don't know what honda do, but if they cycle slower as catalysts degrade and become less responsive, that might explain. just guessing.
show me something [authoritative] that says different then! i've told you what i understand the chemistry to be.
Nothing there to disprove anything I've said so far. The picture shows two ceramic bricks, it doesn't however define that there roles are separate or different.
And that test has long ago been refuted. It is a worthless waste of time.
Precisely my point. (thank you veddy much). Much of what is thought to be true comes from space limited articles in Popular Science type magazines. Things like using an IR temperature gun to diagnose whether a catalytic converter is working for instance...
Are you asking??? Where in any of this did I state that CO is reduced? Do you even understand the difference between reduction and oxidation?
You need oxygen to OXIDIZE HC and CO, if that oxygen can be obtained via the reduction of NOx to N2 and O2 it would certainly make sense to do that process upstream of the oxidation rather than downstream as you assert.
Yes, that is the reduction.
There is, it is attached to the nitrogen (NOx).
Rather than state "modern fuel injection systems" substitute 'modern catalytic converters.'
If I showed you a O2 sensor signal from a 1982 Chevrolet Caprice side by side with an O2 sensor signal from a 2007 Chevrolet Tahoe, you'd be hard pressed to distinguish one from the other. The feed gasses are essentially the same, the O2 content is the same, it's the catalytic converters that have gotten much more efficient. 95% efficiency could only be dreamed of 20 years ago.
That increased efficiency is due to the things I stated earlier, things you said I was wrong about.
The cat is going to heat to 2500* F and reform NOx? Ain't happening.
Which is why I choose to believe what is taught by places like the National Center for Vehicle Emissions Controls and Safety... The "Jim" I know there, have met in person, hosted in -my- government entity emissions testing and training facility 14 years ago at this point is much better credentialed than the one posting here.
Well, I'm not buying you a membership to SAE, so how about you show me where in the above link they describe a different catalytic process between the front brick and the rear brick in that cat-con illustration? They show different feed gasses versus output gasses, hell, they even colored them differently. Hmmm... they show an input O2 sensor but no output O2 sensor, is it possible that drawing is too old to be relevant anymore?
You have no point then. Which part of "This may change in the future" did you not understand?
Word in the pipeline is there may well be a NOx sensor. Then again, we were supposed to have 42 volt electrical systems by now also.
"Rhodium shows some advantages over the other platinum metals in the reduction of nitrogen oxides to nitrogen and oxygen:[31]
2 NOx ? x O2 + N2"
and then:
"palladium forms a versatile catalyst and speeds up hydrogenation and dehydrogenation reactions, as well as in petroleum cracking. A large number of carbon-carbon bond forming reactions in organic chemistry (such as the Heck and Suzuki coupling) are facilitated by catalysis with palladium compounds"
if that doesn't make sense to you, then this conversation can't achieve much.
??? as i said before, one reaction runs at a higher temp than the other. if there's no increase in temp towards the rear of the cat, it's not working properly. /neither/ reaction will occur unless each portion of the cat is above its operation temperature.
non-understanding of catalyst chemistry can lead to fundamental misunderstandings about fault diagnosis - like failing to use an i.r. temperature gun to diagnose whether a catalytic converter is working for instance...
typo. oxidation, not reduction. [i'd have thought that obvious.]
no, modern injection systems do not dump excess gas, thus there is sufficient oxygen in exhaust to ensure conversion. that's why you have "oxygen" sensors.
yes, catalysts /are/ more efficient. but that's helped by the quality of the injection and combustion feeding it. "sensor signal" doesn't determine exhaust content - its just a signal that the injection system utilizes for feedback - it's the injection system that creates the exhaust.
i said you were wrong about the cat. and you were.
then you need to better understand the chemistry! uncontrolled cats overheat, and apart from causing cat problems in their own right, they upset the conversion reaction.
whatever dude. if your "jim" doesn't know what the catalyst materials are and how they work, and he doesn't if you're repeating what he's said to you, then you're both working with what is to you, a "black box" and shouldn't make presumptions about what is inside.
so show me a modern converter that's the single matrix that /you/ think is used. show which regions of the single matrix are palladium-rich and which are rhodium-rich.
i understand it perfectly - and they're not in use, so i bleating about them is a red herring.
aarcuda69062 wrote in news: snipped-for-privacy@news.eternal-september.org:
Well, the reason I asked all this in the first place has to do with Honda's OBD-II system. In addition to the usual P0420, Honda also has a manfuacturer-specific DTC (P1420) that is identified in Honda literature as being: "NOx Adsorptive Catalyst System Efficiency Below Threshold."
Cosidering that Honda uses ordinary O2-sensors downstream, it got me to wondering how it was possible for the ECM to know to set P1420 as opposed to P0420.
Then... I stumbled on a Honda document I've got that explains it. I had found the document earlier, but in my haste I didn't read it carefully enough. It turns out P1420 is set on certain ULEV vehicles that have TWO cats: One is a normal TWC, the other is a "NOx adsorptive TWC". P1420 means the NOx cat has failed its OBD-II test.
100% consistent with my first reply to Tegger. i.e., "rhodium shows some advantages over the other platinum metals." IOWs, all of the noble metals in the cat react with the pollutants, some work better than others. Just as my first reply to Tegger stated.
it won't and not because the above doesn't make sense to me, more because even though you're looking right at it, you refuse to understand it.
So what? That doesn't mean that the temperature will be higher at the outlet.
Anecdotal at best. A test based upon more myth than science.
Oh, so your proof is that the cat won't work unless it's at its operating temperature? Well DUH!.
Indeed!
If that really were the case, then the OEs would have mounted a temperature sensor at the outlet of the cat instead of an O2 sensor to monitor whether it is working. Some functioning cats DO have a higher outlet temperature, some functioning cats however DO NOT have a higher outlet temperature, but to state that all functioning cats must have a higher outlet temperature is flat out wrong. It has been tested and proven to not be the case.
If it weren't the case, I'd be happy to state it as such, but unfortuneately with thousands of temperature tests against thousands of cat efficiency tests under my belt, I can't bring myself to such fabrications.
No, given the erroneous information you've offered so far, I wouldn't have chanced it.
Huh? Who said anything about "dumping excess gas?"
"You have" oxygen sensors because that is currently the cheapest easiest way of determining if the fuel system is in control. Were it not for the necessity of emissions monitoring, the O2 sensors could be eliminated and the engine run solely on the engineers programming.
Apparently, like most, you believe the role of the O2 sensor to be to tell the PCM how much gasoline to introduce to make the engine run properly.
Yes they are, the reason being is due to what I've described here, not because of the obsolete beliefs about design that you've offered.
Hogwash. Take any engine where the injectors go into batch fire mode as limp in mode, you won't be able to measure a difference in exhaust pollutants nor would you feel a difference in driveability.
It doesn't? Funny, I repair stuff every day where the exhaust emissions exceed allowable levels due to a sensor outputing the wrong value.
Really? I fire injectors all the time doing injector balance tests and there is no exhaust coming from the tailpipe.
I'm certain that you believe yourself. Thing is, you're wrong.
An overheated cat caused by what? Are you going to introduce a different premise here?
And your credentials are?
Your last vehicle emissions controls design was when?
It was how long ago that you authored a OE technical service bulletin?
aarcuda69062 wrote in news: snipped-for-privacy@news.eternal-september.org:
I have an infrared thermometer (it cost $75). When I first got it, one of the things I tried to find out was whether or not the temperature of the cat was in fact higher at outlet than inlet.
My results with two cars (both with cats that were known to be working very well) were inconclusive. The aftermarket cat on my Integra showed COOLER at output. But I know from my emissions-test results that this cat was doing a superb job of processing the measured chemicals. The OEM cat on the Tercel showed about 30F WARMER at output. Both cars were driven the exact same manner and distance before I did my measuring.
aarcuda69062 wrote in news: snipped-for-privacy@news.eternal-september.org:
Somewhere I have a magazine article written by a particular Ford engineer (Bill Cannon). This fellow was involved with the very earliest catalytic converter development efforts from the early-'50s up to the mid-'70s.
In the article, Cannon recounts his research team's quest for a suitable catalyst. It was discovered very quickly that the mining industry had already been using platinum-based cats for at least a decade, to control CO in the mines. But since the proposed automotive device needed to be compatible with tetra-ethyl lead (mine-gas was unleaded sub-regular), platinum was unsuitable. This prompted the lengthy search for a different material.
The government body that drove all this in the first place (can't remember the name of it) was initially not concerned with CO, only HCs, which set the focus for the search.
After many years of testing and research -- which revealed that a very large number of metals had considerable HC-catalyst properties -- they settled on tungsten. The test tungsten cats survived satisfactorily for
80,000 miles, this in a day when cars rarely went much past 100,000 miles. Cannon gives charts which show the relative performance of the various tested metals.
Unfortunately, by that time, the government body (can't remember if it was the EPA by this point) suddenly decided that CO must be controlled as well. This junked 20-years of research, and forced everybody back to the original metal, platinum. And that's why they started to phase-out leaded gas.
Since that time, palladium and rhodium have been adopted as well.
This is all from memory, mind you. I'd need to go through a 2-ft stack of magazines to find this article.
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