O2 sensor and emissions

[Vegeta]

My 91 240sx failed emissions. HC and CO were high, but NO was OK. I replaced the exhaust, cat, and thermostat and it failed again.

I got some NGK Vs and an O2 sensor, and I'm trying Marvel Mystery Oil and Techron treatments too. Is there anything tricky with replacing an O2 sensor? It looks like I could just jack the car up, pull the old one near the front exhaust, then plug in the new one. How long should it take? Will I need to measure and cut wires?

By the way, I'm gonna do a write up on my new performance brakes and exhaust soon.

[Vegeta]

After closer inspection, it looks like I can reach the O2 sensor from the top. I haven't pulled it yet. It gets dark too quickly after work this time of year. Still, any advice would be appreciated.

[1991S13]

I have never changed an O2 sensor on any Nissans, but I have on a Jetta and an Avenger. Did your new O2 sensor come with the plug on the end of the wire, or is it just a short little pigtail? On the Avenger I just unplugged the harness and plugged the new in. The Jetta though I had to cut the old sensor off and splice two wires from the new one onto the old wires. It was easy, it helps to know how to solder, but it's not hard at all.

If there was never any antisieze put on the threads when it was installed it will be a ***** to break loose.

Good luck.

[Vegeta]

The new O2 sensor has a metal connector like for car stereo speakers. I'm hoping the old one under the hood has the same. That would be really easy. If not, I've spliced electrical wires before. Thanks.

[TheOne]

it should be easy to change the O2 sensor, go from the top and take it out, it takes a big wrench:)(forgot size).

also spray some WD40 around it before you take it out.(after the engine has cooled down)

[1991S13]

WD40 works good, but B'laster works the best!

Sorry, Im a big fan of B'laster. Works on anything, lol.

[NateDogg]

I would recommend buying an O2 sensor socket. Makes things much easier since it has a slot on the side for the wire to go .

[Vegeta]

Cool. Thanks.

[Vegeta]

I replaced my O2 sensor tonight. I stopped by the autoparts store where I bought an O2 sensor socket ($25) and a 22mm wrench ($8). When I got out to the parking lot, I couldn't wait to try it. I used the 22mm wrench first and the sensor came right out. It is BLACK! This could be why I didn't pass emissions. I'm still gonna replace the plugs and wires and clean the throttle body before I get it inspected again.

Anyway, I took the sensor socket back into the store and showed them my burnt O2 sensor. I got my $25 back and I feel pretty good. Thanks for all your help. NICO good! I'm gonna take some pics and include my O2 sensor in my write up along with my brakes and exhaust.

[Ni2s4s0aSnX]

The O2 sensor the 240sx isnt hard to replace at all. Its right on the side of the header, and if you are going to replace it, its easy to take out because you dont have to worry about damaging it. and if replacing the 02 sensor doesnt solve the problem, then check the egr for leaks in hoses and such.

[driftin2trance]

Anyway, I took the sensor socket back into the store and showed them my burnt O2 sensor. I got my $25 back and I feel pretty good. Thanks for all your help. NICO good! I'm gonna take some pics and include my O2 sensor in my write up along with my brakes and exhaust.

how did u manage to get ur money back?

[ShortyS14]

Apparently he only used the wrench and not the socket.

[Vegeta]

Yeah, I kept the wrench and returned the socket. Good news, I passed today. All of the parts I replaced made a big difference, but it wasn't enough to pass. I replaced the plugs, wires, O2 sensor, thermostat, exhaust and cat, and cleaned the throttle body. Still failed. I finally had to adjust the timing to get it to pass.