Where is the Oxygen Sensor Connect?

[amersbell]

I have an 81 SC. I am replacing the cat with a bypass because it is clogged and old. I was told by previous owner that the oxygen sensor had been deleted, but it is still in the cat. I don't think the wire went to anything. Where does the oxygen sensor connect in the engine compartment and how do you know if they have really deleted it correctly?

[Joe Bob]

Lookin at the motor...there's a port on the left side fire wall.

[amersbell]

But where does it connect to the motor or CIS?

[sjf911]

The wire runs to the Lambda control unit under the passenger seat in a large wiring harness that goes through the fire wall above the right side of the shift-coupler housing.

[amersbell]

How do you know if it was disconnected properly (if there is such a thing)?

[aigel]

Well, it is not correct to disconnect it, unless you go back to a pre O2 sensor CIS setup. You will want to run the O2 sensor in your bypass pipe. If you just unplug the sensor, your cold start and cold idle will be pretty bumpy and you mileage will suffer as well. I had my O2 sensor disconnected at times on my SC, thinking that it made a difference on the butt dyno, but if you read about it, it makes no sense as at WOT the O2 sensor is not taken into account. Maybe the throttle response is a bit snappier, but that's only "maybe"...

George


George

[amersbell]

Is there something that would tell me if it had been backdated to pre 02 sensor time?

[aigel]

Highly unlikey that someone would go back to non O2 sensor setup. But one thing that would be missing is the electronic control box under the passenger's seat. There are other components, like the frequency valve that should not be there. I am not positive where the frequency valve is located on the 911 CIS but you could do a search on that.

Honestly, I don't think it is a good idea to go pre lambda sensor if it is all already there. Most bypass pipes come with a bung for the O2 sensor already installed. If you don't have it, it's a matter of $20 at your nearest muffler shop ...

George

[amersbell]

George,

Thanks, I will keep looking. I do have the lamda box under the seat. I'm guessing it was just unplugged.