Catco 3" and smog... yes another Q. - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Blues13 · 11-04-2003, 02:49 PM

Ok, done some searchin, but didn't find any answers on this..

I'm in cali and I'm trying to pass the sniffer test on my Sr20det..let's say I already passed the visuals. I have a 90' 240sx with blacktop sr and 3" exhaust/dp running @ 10psi.

Problem is: When I took it on the dyno sniffer with the stock cat that came with the car, I failed on the HC levels - max was 121, measured was 135.. so the tech told me to just get a new cat and that should fix it..

So, I come back with a brand new Catco 3" cat, and my car fails again, but this time the HC levels increased to 156 and the NO levels skyrocket so my NO levels fails as well (968max/1390meas @ 15mph and 895max/2145meas @ 25) it was 352 @ 15 and 830 @ 25 using the stock cat. The CO levels with the new 3" cat is better though.

My question is, what the freak is going on,... why is the brand new cat doing worse? And what can I do to fix it? I already changed my 02 sensor and drove the car 30 min prior to the test..

11-04-2003, 02:49 PM	#1
Blues13 Zilvia Junkie Join Date: Jul 2003 Location: OC Posts: 435 Trader Rating: (2) Feedback Score: 2 reviews	Catco 3" and smog... yes another Q. Ok, done some searchin, but didn't find any answers on this.. I'm in cali and I'm trying to pass the sniffer test on my Sr20det..let's say I already passed the visuals. I have a 90' 240sx with blacktop sr and 3" exhaust/dp running @ 10psi. Problem is: When I took it on the dyno sniffer with the stock cat that came with the car, I failed on the HC levels - max was 121, measured was 135.. so the tech told me to just get a new cat and that should fix it.. So, I come back with a brand new Catco 3" cat, and my car fails again, but this time the HC levels increased to 156 and the NO levels skyrocket so my NO levels fails as well (968max/1390meas @ 15mph and 895max/2145meas @ 25) it was 352 @ 15 and 830 @ 25 using the stock cat. The CO levels with the new 3" cat is better though. My question is, what the freak is going on,... why is the brand new cat doing worse? And what can I do to fix it? I already changed my 02 sensor and drove the car 30 min prior to the test..