How can you tell if a cat is working?

[TSMacNeil]

...besides a smog test?

The exhaust guy I used for the 533 last year used a digital infrared temp gun on the cat while the car was running. He seemed very clever about it too. I know my E34 failed CA smog last year. It has a completely stock factory exhaust. I'm reluctant to swap out the OEM cat for an aftermarket based on the general consensus here. Any tricks to proving it works or not? If I recall, my muffler guy was looking for a particular minimum temp on the cat itself...I have a temp gun, and was wondering if I could ascertain it's operation.

I know even OEM cats can get killed by running super-rich for extended time. I don't think that's ever happened with this car.
The last smog test I read showed it was super high on NOX and missed CO too. I'm going to replace the VC gasket as it was recommended and deferred for about a year- and that's a potential VAC issue. I don't know what affects CO at all.

Ideas always appreciated.

[CoyoteStarfish]

http://www.youtube.com/watch?v=Qrj_ioWCkQI

[Patrick McHugh]

"it's gotta burn off the excess fuel"

I would not trust that man

[turbodan]

The only effective way to tell if your cat is working is an e test. Unless its gutted it would certainly work to some extent.

[firefirefire90]

best way to tell is to check your mail and see if it's W-2 has come in

[south26]

My cats never work, they only lay around sleep. So I am not sure how to tell if a cat is working.

Andy

[Mike W.]

The exhaust is supposed to be hotter leaving than entering a cat if it's working well. However BMW insulates their cats, and probably some of the piping on E34s so it may be hard to tell. And a 3 way cat is really two different cats, a front section that is supposed to take care of Nox and the rear which should do HC and CO. Nox is the tough part of course and the front half can fail completely independently of the rear half. In other words no way of knowing without hooking it up to a sniffer.

[TSMacNeil]

Thanks guys. I knew I'd get some feline responses too.
I'll post some test numbers when I get back home of the failed tests.

[wkohler]

I'd take it through here and get it nice and hot first. Test early in the AM if possible. Then see where you're at. You get the free retest in 60 days. No point at throwing cash at the cat before the test. My touring has 212k and has the original cat. I do have to test it this year, though.

[TSMacNeil]

Yeah

I crawled under it yesterday, the whole underside looks brand new. No discolorations. The numbers were horrible the last CA test it took. They put another new t-stat in it and a new 02 sensor. It still sucked.
I think I'll get a valve cover gasket on it, run some hooch through the fuel, and run it through emissions to see where we're at.

Mike, I think you are correct, now I'm recalling this guy was looking for a relative in/out temperature differential...and he kinda knew what it should be too.