Thread: Catalytic Converter Questions

I've been reading about catalytic converters since I'm having trouble passings emissions inspection. I found some interesting stuff and would like to expand the knowledge by asking a few questions.

1. I read that OBDI cats are designed to remove 70% of polluting gases while OBDII cats have to remove 90%. Is there a real difference between pre-1994 Nissan cats and post 1995 Nissan cats?


2. More to the point, can I reduce my B13 emissions by swapping in a late model cat on my B13?


3. My original cat was ceramic core -- are all Nissan OEM cats ceramic, or are some metal screen?


4. I have read that ceramic core cats are more effective at emissions reduction than metal screen cats? Is this true?


5. Has anyone seen any testing for emissions reduction that might help to identify a good performing cat?


Thanks for your input! Still enjoying the ride and regretting the sale of my PL-510 in 1979.

What state are you in? CA and MA are the trend setters, and MA just stopped testing emissions for 1994 and older cars (OBDI).

i have a cat for sale...40 shipped?

most older catalytic converters are used to burn exsess fuel and not really used to convert nox emissions to N2 but they changes that with the newer ones.Why did you fail?

^^^ correct. The only difference is the newer cat convertors have palladium and rhodium in them to help catalyze different gasses. The older cats would do HC and the newer ones do HC, CO, and NOx.

There is supposedly some cars with 4 way cats now that will work to drop CO2 emissions but who knows what cars they are in.

I have not heard about 4-ways. Not sure co2 emissions can be reduced since that is the best combustion path. links?

Read it in tomorrow's technician article a couple of months back about the new convertor. It is supposed to catalyze CO2 into O2, not sure what kind of effect they have gotten with them though

i bet you would pass pretty good with a post 95 cat, what did you fail on?

HC too high + CO too high = Very rich/missfire
HC too high + CO good = Missfire
HC good + CO too high = Running too rich
CO good + NOx too high = Lean or too much timing

This is just a guide to help you figure it out. I have seen this in many cars, there are exceptions to this, but for the most part these readings are what you get.

Thanks for your responses, guys. I've been out of town and so have not been on line.

Let's see --

I'm testing in MD. It's the standard dyno test for emissions. I have not heard anything definite about stopping these tests for OBDI cars in my state.

I'm running 1.4 HC when the standard is 1.1. NOX is passing, but very close. The major problem with HC is early in the test when accelerating in 2nd and 3rd between 2000 and 3000 RPM. Cruising at 55 MPH later in the test is fine with low HC and NOX. You can see the test results here http://www.sr20-forum.com/showthread.php?t=9162

I called a cat distributor that had a good site on the web. The guy suggested that I lean out the mixture a little (I can drop fuel pressure -- I know that if I change the fuel pressure 3 psi it moves the AFR half a point across the board). Or, he suggested an OBDII cat as a possibility -- but no promises. Problem is there is no direct-fit OBDII cat for the OBDI exhaust. The OBDII cat that he sells is a different size (my stock cat is 13" long, he has a 16"x2.5" OBDII with no flanges).

Still considering options....

Thanks again for your input.

Bill