Catalyst Control Function

[CCycle]

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

 

[Aquaduct]

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.

 

[patprimmer]

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.

 

[Aquaduct]

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.

 

[icrman]

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.

 

[Aquaduct]

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.

 

[CCycle]

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.

 

[ben91932]

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

 

[Aquaduct]

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.

 

[GMcNally]

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

 

[ben91932]

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

 

[Aquaduct]

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.

 

[toytech]

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?