exhaust sys. ???'s O2 sensor - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

s14slide · 01-01-2003, 03:13 AM

well I've searched this forum high and low and have yet to find an answer. On an s14('95 specifically), w/ a hotshot header, high flow cat and cat back, how important is the second O2 sensor? Does it have to specifically be put in the exhaust stream after the cat, or does it matter? I've heard that it has to get a reading after a cat and that w/ it either not hooked up or hooked up before the cat, you'll get a lean mix which will rob power and cause engine damage and also get that damned check engine light. My headers did not come w/ a provision for the second O2 sensor. Again, this is all hear-say info and I'm hoping someone w/ maybe an FSM will be able to answer my questions. Thanks in advance.
And Happy New Year's.
This year call's for a KAAZ and a set of FLT-A2's. Wooohoooo!!!!

Edit for grammar and spelling.

logo20 · 01-01-2003, 01:45 PM

I don't know much about this but i'll try to help. the header is supposed to have only one o2 sensor. I don't know if the 95 model have a second o2 sensor, but if it does (go check) you should put a catback with the second o2 sensor. like you said the engine light is gonna come on, and fuel ratio is gonna be messed up.

**mrmephistopheles** · 01-02-2003, 01:42 AM

Both 02 sensors are necessary for your car to run right. I may be recalling incorrectly, but I think the 2nd 02 sensor is just before the cat. Someone with an S14, speak up.

edit: just before the FAKE CAT. someone slap me.

s14slide · 01-02-2003, 09:24 AM

I should have added that the second sensor was located right between the stock cat and the stock resonator(cat lookalike). But now w/ the full exhaust system, the o2 sensor won't reach to behind the new cat. I hope I'm not too confusing.

Foxcolt · 01-02-2003, 10:19 AM

The second 02 sensor is just their to make sure the first one is working correctly. As long as you have it in there somewhere you won't have a problem.

s14slide · 01-02-2003, 10:38 AM

cool thanks, I guess I won't have to extend the wires to reach behind the second cat. Hope your right cause I don't wanna tap a hole in the piping then have to fill and tap in a different location. Waste of time and money. Correct me if I'm wrong, but doesn't the second O2 sensor get after cat exhaust hence the "primary cat failure" fault code. Just wanna be sure be sure before my exhaust setup ends up being swiss. Not trying to come of like an a$$. Just want facts before I get drill happy. Thanks.

Anybody w/ an FSM for a '95 got anything. Sorry for seeming a bit paranoid about a small thing, but being a military aircraft mechanic makes you paranoid about "by the book."

01-01-2003, 03:13 AM	#1
s14slide Zilvia Addict Join Date: Sep 2002 Location: Nippon Age: 43 Posts: 630 Trader Rating: (0) Feedback Score: 0 reviews	exhaust sys. ???'s O2 sensor well I've searched this forum high and low and have yet to find an answer. On an s14('95 specifically), w/ a hotshot header, high flow cat and cat back, how important is the second O2 sensor? Does it have to specifically be put in the exhaust stream after the cat, or does it matter? I've heard that it has to get a reading after a cat and that w/ it either not hooked up or hooked up before the cat, you'll get a lean mix which will rob power and cause engine damage and also get that damned check engine light. My headers did not come w/ a provision for the second O2 sensor. Again, this is all hear-say info and I'm hoping someone w/ maybe an FSM will be able to answer my questions. Thanks in advance. And Happy New Year's. This year call's for a KAAZ and a set of FLT-A2's. Wooohoooo!!!! Edit for grammar and spelling. __________________ = My day

01-01-2003, 01:45 PM	#2
logo20 Zilvia Junkie Join Date: Apr 2002 Location: Houston, TX Posts: 345 Trader Rating: (0) Feedback Score: 0 reviews	I don't know much about this but i'll try to help. the header is supposed to have only one o2 sensor. I don't know if the 95 model have a second o2 sensor, but if it does (go check) you should put a catback with the second o2 sensor. like you said the engine light is gonna come on, and fuel ratio is gonna be messed up. __________________ http://community.webshots.com/user/logo20

01-02-2003, 01:42 AM	#3
mrmephistopheles Magnanimous Justice Distribution Service Join Date: Mar 2002 Location: BFE Age: 23 Posts: 14,372 Trader Rating: (9) Rides Gallery: mrmephistopheles Feedback Score: 9 reviews	Both 02 sensors are necessary for your car to run right. I may be recalling incorrectly, but I think the 2nd 02 sensor is just before the cat. Someone with an S14, speak up. edit: just before the FAKE CAT. someone slap me. Last edited by mrmephistopheles; 01-03-2003 at 12:48 AM..

01-02-2003, 09:24 AM	#4
s14slide Zilvia Addict Join Date: Sep 2002 Location: Nippon Age: 43 Posts: 630 Trader Rating: (0) Feedback Score: 0 reviews	I should have added that the second sensor was located right between the stock cat and the stock resonator(cat lookalike). But now w/ the full exhaust system, the o2 sensor won't reach to behind the new cat. I hope I'm not too confusing. __________________ = My day

01-02-2003, 10:19 AM	#5
Foxcolt Zilvia FREAK! Join Date: Apr 2002 Location: Northern VA Posts: 1,264 Trader Rating: (0) Feedback Score: 0 reviews	The second 02 sensor is just their to make sure the first one is working correctly. As long as you have it in there somewhere you won't have a problem. __________________ Driftec www.midatlantic240sx.com

01-02-2003, 10:38 AM	#6
s14slide Zilvia Addict Join Date: Sep 2002 Location: Nippon Age: 43 Posts: 630 Trader Rating: (0) Feedback Score: 0 reviews	cool thanks, I guess I won't have to extend the wires to reach behind the second cat. Hope your right cause I don't wanna tap a hole in the piping then have to fill and tap in a different location. Waste of time and money. Correct me if I'm wrong, but doesn't the second O2 sensor get after cat exhaust hence the "primary cat failure" fault code. Just wanna be sure be sure before my exhaust setup ends up being swiss. Not trying to come of like an a$$. Just want facts before I get drill happy. Thanks. Anybody w/ an FSM for a '95 got anything. Sorry for seeming a bit paranoid about a small thing, but being a military aircraft mechanic makes you paranoid about "by the book." __________________ = My day