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Old 07-22-2016, 06:44 PM   #1
Join Date: Apr 2016
Location: los angeles
Posts: 25
Failed California smog; need new cat?

Well, I'm trying to register my 89 325iC. It failed smog when I first picked it up, due to a capped vac. line and high HC and NO. The car had been neglected for awhile, and I knew it wouldn't pass smog as is.

It was running with a rough idle and was running rich, so I changed the ICV, spark plugs, replaced the fuel injectors, air filter, and coolant temp sensor. Castro Motorsports found a vac leak, adjusted the valves, and adjusted the TPS. At this point, it's idling pretty well.

Went back into the smog test, and my numbers were slightly worse.

I checked the temperatures of the exhaust pipes with an IR gun-style thermometer and found that the pipe was around 280-300F before the catalytic converter, and maybe 280-350F right after. Also, can NOx get that high with a good cat?

So, have I missed anything obvious, or am I due for a new cat? Did running the car rich by PO ruin the cat?

If I am, any good shops in the San Fernando Valley? Or is this easy for any muffler shop? I've never had to get a new cat on any car, but I figure it's not a DIY job unless you've got a welder.

Here's the numbers:
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chemprof is offline   Reply With Quote
Old 08-06-2016, 09:57 AM   #2
Join Date: Mar 2014
Location: Sacramento, CA
Posts: 89
The IR measurements you got imply you may need a new cat. In fact barring some other issues with the motor (which it sounds like you've gone over pretty extensively) those numbers seem quite high as well.

Every car i've smogged after getting a new cat (all of them 80's cars with over 200k miles on the motor) have passed with barely registering any emissions. I'd say bite the bullet and get a new cat see where it gets you.
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Old 08-06-2016, 02:03 PM   #3
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Streichholzschächtelchen's Avatar
Join Date: Jan 2009
Location: Alameda, CA 510
Posts: 1,596
Rev the piss out of it for an extended period of time, 3rd and 4th gear on highway. Get your cat so hot nothing escapes.
Jah bless!
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Old 08-19-2016, 01:09 PM   #4
Join Date: Apr 2016
Location: los angeles
Posts: 25
As a follow up to anyone who finds this...

One aftermarket Cat = passed smog! Win!

NOx was 13 and 9 (!)
CO was 0.03 and 0.02 (!)
and HC went to 49 and 23 (about average)

I didn't even bother getting it particularly hot before I got to the test too.

And if you're looking for an OEM cat, the dealer told me the only ones were in Germany for $1500.
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Old 11-26-2016, 08:04 PM   #5
Join Date: Aug 2016
Location: Los Angeles
Posts: 86
New cat may be a temporary fix. I'd recommend performing compression and leakdown tests. I have the same issue, slightly rough idle that feels like a cylinder is missing. Turns out cyl 6 had leaks from both valves and wasn't firing at all, instead dumping fuel through the exhaust. New cat will clear out the unburnt fuel but only work for a year at most before rare metals burn out inside.
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