My '99, 3.8, is throwing po420 at me when scanned, but that's all. I've read the other posts about this cost and I think every ove have them has it accompanied with po301-306 to indicate a misfire. I had this code come up a few months ago and I read (in another forum) that cleaning the Mass airflow sensor can help that, and I also found a vacuum leak. Don't know if they are truly related, but I did those things, cleared the code, and all was well until very recently.

My car seems to be running fine.

Please tell me there is another common cause for this code BESIDES a cat that's possibly going bad!

Thanks,
^JR^

 

found this on the net

The PCM copares switch rates between the front O2 sensors and the downstream catalyst moniters. The catylist moniters are often mistaken as O2 sensors, and they are, but that is not their job, or what they are called. By comparing the switch rates between the front (before cat) and rear (downstream of cat) the PCM knows if the cat is affecting the exaust, and how much it is affecting the exaust. If it sees little or no effect o the exaust gases that have passed through the cat, then it decides that the cat is not working anymore, ad sets a P0420, or a P0430, depending on which bank it is. To check this yourself, you will need to bring up data stream on your scanner, watch the upstream and downstream O2 parameters and see if they are following each other closely. If the cat is working right, you should see a fairly rapid switch rate, probably 5 or 6 times a minute on the front O2, but almost a flat line just above .5 volts on the rear. If the rear is switching often you proabably need a catalytic converter.

 

haha pretty much what the guy above me said i do emissions inspections for the state of nevada and the only reason for a p0420 code is failing or disconnected oxygen sensors or a bad catalytic converter... and catalytic converter are usually only good for about 10 years

 

Thanks for the info.

I don't personally own a scanner. Can I use a voltmeter to check those sensors?

I'm thinking that if the cat has to go, it will be time to do some stuff I've had my eye on like add a set of pacesetter headers.

All I can find on Summitracing.com are direct fit cats that would have to be cut to fit the headers. I'm sure I can find what I need elsewhere. I'll keep looking. The question now is (and I apologize in advance if its a stupid question) does the cat HAVE to be welded to the Y-pipe? Can I get away with clamping it? I don't know how to weld and can't think of anyone I know that does or even has the equipment. The object, of course, is to keep from being reamed by a muffler shop for boat loads of $$$$.

Thanks again.

^JR^

 

ummmm to the best of my knowledge cats need welded.... my personal favorite cat is gunna be magnaflows high flow cat.... idk where you are but the shop i went to in vegas welded the cat in place for 40 bucks.... i did buy the cat through them though

 

If I went the new header/cat route, I guess I'll have to have the S pipe fabricated since I can't seem to locate one that comes with a cat and is vehicle specific to mine (is that what its called? - the outlet pipe leaving the cat).

Guess I can still hope the sensor is going bad.

^JR^

 

u mean like this

http://www.summitracing.com/parts/MPE-23466/

 

I was probably confusing in my last post. A chronic failing of mine.

That's a direct fit which would be fine if I didn't want to add headers (providing my cat needs to be replaced to start with). But the y-pipe that comes with pacesetters, for example, is different (obviously). To use the cat in that link, I'd have to cut the y-pipe off of it and have it welded to the pacesetter pipe.

Maybe I'm just a little timid about cutting a brand new $300+ part to make it work.

I've found plenty of cats by themselves, but no s-pipes. So, I figure I'd have to have one fabricated to fit. More $$$.

Oh well...The headers are more of a want, than anything else. So I'll probably end up keeping my manifolds and using a direct fit, then add a cat-back system. Anyone using the Flowmaster American Thunder system on their 3.8? That one looks easy enough to install.

Thanks, again, for the replies
^JR^