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Catalyst Control Function

Catalyst Control Function

Catalyst Control Function

(OP)
I would appreciate information on catalyst emission control function.
It looks like this is the board to get that information.

The particular car,  '98 Buick 3.8 liter.
It ran ok up to about 70 K miles where upon the check engine light came on.
Code check says low catalyst activity.
There is no after-market catalyst available.  GM 's price $500 and about $1000 installed.
I bought an after-market catalyst which is the same size and looks similar.
Cut the flanges off the original catalyst and welded them on the after-market unit.
Well that ran about 15 K miles and we get the low catalyst activity code again.

Now for the questions:
1.  I understand the engine control modulates the air/fuel ratio each side of stoichiometric.
     What is the frequency and approximate swing of this modulation?

2.  How do the O2 sensors work?  I understand that the voltage swings from about 0.9 to 4 volt.  
     Do they self generate this voltage or is it sinking externally supplied current?
     What is a typical internal impedance of a sensor?

3.  I read about various "washes" to activate catalysts.  
     Are these available?  Would it do any good to do this myself?

Thanks, Km

RE: Catalyst Control Function

To start you off..
1. the ox sensors modulate the fuel system in closed loop configuration. The sensor is an input for control.
2. the ox sensors must operate at over 600 degrees (as well as the cats) and generate a voltage output related to oxygen content.  The output swing is normally .1 to about 1 volt.
The impedence can't be measures by the standard meter without risking damage.  The actual impedence may be quite different at operating temp.
3. there are some chemicals that will tend to clean off deposits from the catayst substrate.
...
My sense is that you have some other fault causing the problem.
Air injection, if the car uses that system may not be operating the cat at high enough temp.
An air leak ahead of the cats.
Fuel system running to rich.
Leaking fuel injectors.
Something in the fuel may be contaminating the cats.
Since the problem has returned, I would assume the cats are a secondary result problem and is the only way the engine control system has to alert you by lighting the MIL lamp and setting a code as the (end) result.
Forgive me a bit if I am inaccurate about GM, as I am totally familuar with Ford systems in relating to these functions but they all work much the same.

RE: Catalyst Control Function

Or, you are blowing enough oil through the piston rings to foul and/or poison the catalyst.

RE: Catalyst Control Function

EP additives in oils can poison cats if the engine is burning oil.

Regards
pat   pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Catalyst Control Function

There are two types of O2 sensor, narrow band (which is probably what you have) and wide band. Not electrically interchangeable. Narrow band jump between lean and rich at approximately 0.45 volts. Wide band are nearly linear with F/A ratio. If you bought the K&L F/A meter ($200) you wasted your money. The narrow band sensor cannot give meaningful output on how rich or how lean, only rich or lean. A dot mode driver, bargraph LED and sensor is all it is.
There are several different types catalytic converters available. The first only converted hydrocarbons, the later CO and then NO2. Find out which yours is supposed to have. Some also use air injection.
You can check your sensor with a propane torch, digital volt meter and a pencil. Heat the sensor with the torch, then burn the pencil between the torch and sensor. Check fo a lean/rich voltage change. Look up O2 sensors on a search and you will find lots of information. For $35 or so for a new sensor it may not be worth it.

RE: Catalyst Control Function

I didn't see you mention- how is the health of your downstream O2(s)? Is it working correctly? OBD2 mandates that the catalyst function, and anything else that can affect emissions must be monitored. If the ds O2 is bad it might be false coding.

TurboTR

RE: Catalyst Control Function

(OP)
Great info.   Thanks a lot.

More on the car:
1.  The car runs great. I change oil when ever it tells me to which is about 6K miles.
     The oil is not down much and we have never added any oil.
     It gets low to mid 20s mileage.

2.  I understand the catalyst is a 3 way.
     There is no build up in the exhaust system .
     The catalyst brick is clean.

3.  I did change both O2 sensors.
     The first one did go bad according to the code reader.

4.  I have not purchased any analyzer equipment other than a OBDII code reader.
     But I was considering building a virtual O2 sensor for use in leu of the second sensor.  
     The signal would be derived from the first sensor, delayed and sent to the control system.

RE: Catalyst Control Function

Hmm. So you say the primary O2 went bad? When did you replace the sensors? Does the car lose any coolant at all? Are the exh headers tubular low grade stainless? If so they can crack, and that might throw things off severely. The turbo Buicks were notorious for cracking the ps side.

TurboTR

RE: Catalyst Control Function

(OP)
TurboTR,  It is not turbochanged.  The exhaust system is tight as far as any inspection can show.  There is no noise like a leak makes.
We have never had to add coolant.  But one time about 80 K miles I noticed some coolant on the floor under the car.  I could not define where it was coming from other than it was high up on the engine.  I was hard pressed for time right then so I took it into the dealership.  They changed the intake manifold which I understand is plastic and all go bad.  Some coolant could have gotten in the engine but it wasn't much.

As for the O2 sensors,  The car started showing codes around 70K miles. The codes were P0131, O2 sensor Low Voltage Bank 1 Sensor 1 and P0420, Catalyst System Efficiency Below Threshold Bank 1.  I changed the first O2 sensor.  It then showed P0420 code only.  So I changed the second O2 sensor.  It still gave the P0420 code.  So I changed the catalyst.  No more codes for about 15K miles where upon the P0420 code is back.  

RE: Catalyst Control Function

Could you clarify which O2 sensors you changed?  I was under the impression that these cars had three sensors, two pre-cat and one post-cat.  This sort of problem, as TurboTR says above, is usually indicative of the post-cat sensor going bad and this would be consistent with the mileage on the vehicle.

RE: Catalyst Control Function

(OP)
Eric,  This car has two O2 sensors.  One before and one after the catalyst.
Both of the sensors got changed but not at the same time.  See sequence previous post.

Thanks for your interest and info.

RE: Catalyst Control Function

As far as the frequency and swing of the a/f modulation, roughly, at low speeds it could be in the range of 10-30+ or so per second say. At higher speeds maybe 40-60+ or so. Again, roughly; your mileage may vary :) The older GM scheme used a variable called O2 crosscounts that maintained a running, rollover count of the number of crosscounts. The time period we were used to looking at per counter update ('87 Grand National 3.8L) was 1.4 sec, the udpate rate of the ALDL scantool data output from the ecu.

The a/f swing, I would guess probably say +/- 1 a/f ratio or less might be a reasonable goal. Just a guess though in this case...

TurboTR

RE: Catalyst Control Function

Re: a/f swing, FWIW, I do SCT tuning for late model Fords, and we generally have a wideband hooked up to the car as well. I generally see an a/f swing that fits what I posted above. Hope that helps some.

TurboTR

RE: Catalyst Control Function

(OP)
TurboTR,  I believe you are telling me that the a/f ratio crosses stoichiometric 10 to 50 times a second!  What then is the criteria for showing a P0420 code?

Some GM literature I saw someplace said the low catalyst activity code (P0420) was determined by the time difference in transitions between the first and second sensor.  But if the a/f swings are fast enough a rich or lean edge may never break through the catalyst.

RE: Catalyst Control Function

Yes. Who knows, maybe there is even a special diagnostic routine the ecu runs occasionally to check the catalyst health :) Unfortunately I don't know the details of how that part is monitored.

TurboTR

RE: Catalyst Control Function

The ecu looks for the upstream O2 sensor and downstream O2 sensor output to be "in phase" so to speak,  rather than looking purely at lean vs rich.
If they're out of phase, it assumes the cat's gone bad.
Something you could expect in 15K miles from an aftermarket cat - why do you suppose it was so much cheaper?

 - R

RE: Catalyst Control Function

Unfortuneately, you've made a mistake. It isn't your fault, but you're down the road already.

You've got an OBD2 vehicle. The fore and aft O2 sensors monitor oxygen storage in the catalyst. As the catalyst deteriorates, O2 storage also decreases. The light illuminates when the control system determines that catalyst function has deteriorated to the point that the car is emitting more than 1.5 times the regulated amount of some pollutant. The cat efficiency is probably 85-95% at that point. By hooking up an aftermarket catalyst that isn't designed for the engine, you're burning it up in the same manner only faster.

The mistake you made is that the catalysts (as well as the O2 sensors and the ECU) are emmission related components that, by law, are warranted to 120,000 miles or 8 years, regardless of the warranty on the rest of the vehicle.  If you would have taken it to the dealer, it'd be free.

Sorry.

RE: Catalyst Control Function

Aquaduct

CCycle did not say where he is. Are you sure that law applies to everywhere a 1998 Buick 3.8 litre might live.

If the law does apply to CCycle's location, it might be a bit naughty, but fair seeing as the original cat failed, if he was to use a second hand cat and get that replaced under warranty if it fails.

Regards
pat   pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Catalyst Control Function

Pat,

I was in Powertrain Engineering at GM's crosstown rival for most of the '90s.  I've been in heavy trucks for the last 5 or 6 years, so my memory may be a bit fuzzy on some details, but I'll try to help.

OBD2 is a mandated part of the emission system both Federally and in California (there are some minor non-technical differences).  Canada adopts US standards so it's good there too.

Different states and smaller jurisdictions have different ways of enforcing it, however. California, for instance, requires that the Check Engine light be functioning but not illuminated (comes on for a couple seconds at start and then goes off) before they'll renew your plates. If CCycle lives in one of these jurisdictions, there's a paragraph or 2 on the emissions warranty in the Owner's manual (small and tough to find, but the Feds say it's gotta be there) and if he went to the dealer and told the sad story of what he's done, he may be able to talk them into doing the warranty work (heck, they'll just bill it back to the General). Some proof like receipts may help and I'd bet the old parts would really do the trick but that's up to the warranty system.

Most jurisdictions don't enforce it at all. Several years ago my light came on in my '96 Aerostar (I live in Virginia) for a similar Evaporative Emission system problem. The EVAP stuff isn't under that warranty. I ignored it and 2 years ago, the light burnt out. No more problem. These failures don't cause operating problems, they just annoy the crap out of you. If he's too impatient to wait for the "burnt bulb" fix, some black electrical tape will do.

RE: Catalyst Control Function

Aquaduct

Are Buicks sold or privately imported into areas outside USA and Canada?

We haven't seen them here since the 60's, But GM here uses their V6 in a locally designed and made car, and we require OBD2 standards to be met and maintained, and checked via yearly roadworthy inspections after the car is 3 years old, and occasional impromptu or random inspections by the EPA

Regards
pat   pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Catalyst Control Function

Sorry Pat, not paying attention to the fact that you're outside the US.  I assume CCycle is in the US since his post is in miles.

Don't know about Buick in Australia.  The 3.8L has been a fairly common engine in many GM vehicles for years.  I'm guessing GM builds cars in your country, although possibly not as we'd recognize them over here.  They can also be imported. They certainly could borrow components from other countries even if they're unique to Australia.  My old company built Falcons in Australia although we never saw them over here.

Typically, there are 3 major automotive standards in the world, Europe, US and Japan.  Most other countries adopt some variant of those 3.  For instance, although the US has 2004 standards, many countries have adopted US standards from 1984. Depends a lot on infrastructure, particularly available fuels, etc.

Don't know specifically about Australia, but it wouldn't be surprising if you had adopted OBD2 from the US.  In which case, yeah, it's probably the same system. Of course, the US Environmental Protection Agency isn't enforcing anything over there.

RE: Catalyst Control Function

OK

I must admit I missed the miles clue.

They don't import Buicks here, and it would be very difficult to convert to right hand drive unless a RHD model is made which I doubt.

We have a GM locally produced car called a Holden. It competes head on with the Falcon. It used until very recently a GM 3.8 litre 90 deg V6 with a gen 111 5.7 litre V8 option.

The coup version is exported to the US as Pontiac, so you probably have seen one.

We do use similar emission standards to the USA I think. We certainly do have OBD2 conformance.

I do get a bit sensitive (maybe over sensitive) when Americans presume that all posts are made from the USA, or that US law applies to the rest of the world.

Anyway, this is enough of the off topic digression, ans sorry for getting a bit to toey about the other than USA thing.

Regards
pat   pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Catalyst Control Function

And I am sorry for that.  You're right.  I'm new here and not quite acclimated.  In general, I should be pretty good about it.  My company's headquarters is in Sweden and we sell in Australia also.  I should be used to it by now.

RE: Catalyst Control Function

Aquaduct are you sure it is 120,000 mile or 8 years?
I have only found reference to 80,000 miles.
I would like to know for sure.

RE: Catalyst Control Function

No, I can't be sure anymore. Emissions durability was 120K, but, like I said, that was a long while, another industry, and a whole bunch of similar sounding numbers ago. I know they have to spell it out in the manual. If it says 80K there, then that's it. Sorry.

RE: Catalyst Control Function

(OP)
I spent an hour looking through the owners manual.  I do not find a single reference to the catalyst system.  The owners manual is most intellectually insulting.

My opinion, and note that this is just an opinion based on my experience and the experience of others I have observed, there is a lot more trouble with catalyst systems and check engine lights that is generally admitted.

I am in the States, fortunately in a state that does not hassle people on emission systems.

Thanks much for the discussion.  I have learned.  This board has great info.

RE: Catalyst Control Function

A couple of things...
The ECU needs to see the pre-cat 02 swinging between appx .2v and .8v very rapidly;  and the post-cat 02 swinging from appx .4 to .6 very slowly so that it can verify that the cat is doing its job.
Cats on OABD-11 cars are finely tuned to the engine management  system, and the fact that the generic cat failed to set a code  immediately was pure luck.
You'd be lucky to get a dealer to honor their emissions warrantee with that cat welded in, and in California at least, selling used cats is illegal, so you'll be hard pressed to find a used one to bolt in....
Lastly, most cats are killed by long term exposure to slight misfires. You'd be wise to get a *very* competent tech (one experienced with scanners, dso's, current ramping etc) to give your car a close look to see what caused the cat to fail.

hth,
Ben

RE: Catalyst Control Function

OBDII also contains misfire monitors to look for the level of misfire that can kill catalysts. Usually in the range of 1-5%. Your catalyst didn't die. It just wore out prematurely. Could be caused by anything from a tank of off-spec fuel to unusual driving habits to normal six sigma wear.

If you take it to a tech, no matter how competent, and get him chasing misfire levels that low (particularly if there's no misfire codes) you'll be spending another butt load of money chasing phantoms that you can't reach. I think you've over spent on this already. Let it go.

And thank heaven you don't live in California.

RE: Catalyst Control Function

Hello

Regarding warranty:  It is my understanding that the vehicle manufacturer may not be obligated to provide warranty coverage beyond 3years if the vehicle is garaged in a state/province where there are no emissions testing programs implemented.  

Regarding the P0420 Catalyst efficiency code:

The test runs at idle, after the catalyst has been warmed up.  The PCM is testing OXYGEN STORAGE CAPACITY of the converter.  If you have installed an aftermarket converter, it probably is not meeting the minimum oxygen storage capacity requirement for OBD2 .  Pre-obd2 converters will work quite well at reducing emissions output, but be prepared to live with the check engine light if you choose to install one on this vehicle.

During this test (done at idle after a minimum drive time as specified below) the mixture is driven rich and lean.  The amount of time it takes for the POST CATALYST oxygen sensor to respond to these mixture changes indicates the amount of oxygen storage in the converter.  

Here are some specifics on the code:

DTC P0420
Conditions for Running the DTC:

Meet conditions for engine warm up. Use the scan tool catalyst data list in order to verify the following.
 
No VSS sensor, TP sensor, EVAP, HO2S sensor, misfire,
IAT sensor, MAP sensor, IAC sensor, Fuel trim, EGR, ECT sensor, MAF sensor, or CKP sensor DTCs set.

Engine has been running longer than 10 minutes.

Engine coolant temperature (ECT) is above 76°C (168°F).

Baro is above 75 kPa.

Vehicle is in Closed Loop.

Intake air temperature (IAT) is above -29°C (-20°F) and less than 100°C (212°F).

Warm up the catalyst.

Fully open hood.
Transmission is in park (automatic) or neutral (manual).
Set the parking brake.
Engine speed is greater than 1500 RPM for 1 minute.
Return to Idle.

Test the catalyst.

Transmission is in drive (automatic) or neutral (manual).
With in 5-20 seconds the air fuel ratio will go lean above 15.3 for up to 7 seconds, then it may go rich below 14.1 for up to 7 seconds.
Using the scan tool check and see if DTC P0420 has passed or failed this ignition cycle

Conditions for Setting the DTC
The PCM determines that the catalyst's oxygen storage capacity is below a threshold considered acceptable

Hope this is of help.

G.McNally
Ontario, Canada

RE: Catalyst Control Function

Aquaduct (Automotive)      Dec 28, 2004
<<OBDII also contains misfire monitors to look for the level of misfire that can kill catalysts. Usually in the range of 1-5%. >>

Misfires are counted and reported by the scantool as the number of misfire events per number of revolutions.

<<Your catalyst didn't die. It just wore out prematurely.
 Could be caused by anything from a tank of off-spec fuel to unusual driving habits to normal six sigma wear.>>

Normal lifespan for that cat is appx 10 years or 150K miles.
Something killed it (wore it out..whatever...) Maybe a slug of bad fuel (ever run leaded fuel?) or maybe the coolant leak you mentioned or using the wrong oil, or the missfire thing.

<<If you take it to a tech, no matter how competent, and get him chasing misfire levels that low (particularly if there's no misfire codes) you'll be spending another butt load of money chasing phantoms that you can't reach.>>

What if there are misfire codes, and there is a minor problem that is easily repaired, maybe even under warantee?? Minor misfires will not turn the check engine light on, but can be detected by a scantool. If left alone for the next few years, how much fuel will be wasted? Enough to make it worth the $150 or so a *good* technician will charge to take a look?? A crap shoot for sure, unless you live where emissions inspections are done.. then its kinda unavoidable.

<<And thank heaven you don't live in California.>>

I kinda like it here, and can remember the days before the smog check program and the brown skies, watery eyes etc.
I *have* to keep all my cars running well enough to pass emissions tests to keep them registered, and dont mind at all. Small price to pay for clearer skies.

Ben

RE: Catalyst Control Function

OK, CCycle, if you've got misfire codes, get 'em fixed.

However, he made no mention of them and he said that the car is running fine otherwise.  I don't think there's a detectable significant misfire problem. And paying someone $150 to look around for something that in all likelyhood isn't there will only agravate his present situation. Of course, that's if the tech is really, really knowledgeable and honest. Most guys, if you insist there's something there that needs fixing, they'll be glad to find something wrong, which may be more than $150.

And, like I said, he's only talking about a cat that's running 80-90% when it sets the light. I know, I was there when the whole system was dreamed up. His cat would have easily lasted 150,000 miles with at least 50% efficiency. He'd never have known the difference if the light hadn't have triggered.

Actually killing a catalyst is usually due to misfire or some other high exhaust temp situation. But normal catalyst deterioration has many other causes like sulfur poisoning, water degradation, thermal gradients, manufacturing variability, etc. If the catalyst were actually dead (yes, the semantics make a difference), than he'd probably have an engine problem that a tech could fix.

The guy's probably got $200 into a problem that really impacts him very little and by not knowing about the emissions warranty, he was aced out of the only effective repair (replace the catalyst with the OE one). If the burden of his conscience so moves him, he can do something about it.  But his local area doesn't have California's problem, so they don't require such draconian measures. One of the benefits of not living there. He should know the situation accurately before he makes the decision to drop more of his dough.

And I'm glad you like California. Stuff lke this is one reason I don't.

RE: Catalyst Control Function

fyi being one of the guys who fixes this stuff, most of the time a po420 will not come back if reset for some time if at all usually not at all, I have seen this repeatedly in the field, perhaps a bad tank of gas or some other transient condition that reduces combustion efficiency enough to effect the catalyst in the short term.  An aftermarket catalyst will seldom make it past a year without a repeat of the code, and in my experience most don't last more than a couple of years anyway.  After all, how much platinum can you put in a 100 dollar cat anyway?

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