O2 Sensor and Cat bypass Pipe

[Swiftmotoring]

Is an O2 sensor necessary when the catalytic converter is replaced with a cat bypass tube? Thanks

[KNS]

If the rest of the system is in place then - yes.

[Roger 911]

Or you could change your chip to a Euro spec, which did not use an O2 sensor. This also assumes you don't have to pass an emission test.

Roger

[Swiftmotoring]

Thanks for the quick answers. Yes, the rest of the system is in place. The car is surging as if it is running very lean at normal speeds, it is fine when accelerating.

[Swiftmotoring]

And no, the emission test is not a requirement....

[theclaw]

If smog is not an issue plug the O2 sensor, disconnect it, get the chip mapped properly and zoom zoom.

[McLovin]

Originally Posted by Roger 911

Or you could change your chip to a Euro spec, which did not use an O2 sensor. This also assumes you don't have to pass an emission test.

Roger

Originally Posted by theclaw

If smog is not an issue plug the O2 sensor, disconnect it, get the chip mapped properly and zoom zoom.

What "chip" are you talking about in a 911SC???

[Roger 911]

Originally Posted by Swiftmotoring

And no, the emission test is not a requirement....

Oops, I just noticed this is an SC, so no chip. Not sure what you'd have to do to run without an O2 sensor with the CIS. But I'm sure there are plenty of posts if you do a search.

Good luck.
Roger

[theclaw]

Originally Posted by McLovin

What "chip" are you talking about in a 911SC???

oops.

(I just needed an excuse to replay my exhaust clip)

[Roger 911]

Originally Posted by theclaw

oops.

(I just needed an excuse to replay my exhaust clip)

And we thank you for that!

[KTL]

The O2 sensor on a SC is often recommended to be disconnected on the forums. Guys who have serviced these cars for many years just don't bother with it because it does a poor job benefitting the engine tune.

On the later Motronic equipped cars, yep you need the O2 connected or the ECU will run in "open loop" mode because it is looking for feedback from the O2 sensor and not receiving it.

Yes you can run without the O2 sensor on the Motronic if the chip is reprogrammed to Euro specs. Also some simple wiring you need to clip/jumper if i'm not mistaken? But I would think for the most part the O2 is a good thing? It's constantly monitoring the mixture and attempting to make what adjustments it can to maintain a certain lambda value, assuming everything is functioning properly. And you can have the best of both worlds with your O2 system intact. You get some economy when the O2 is functioning during part throttle operation and programmed performance when it is bypassed by design by the WOT (wide open throttle) switch.

[Bob Kontak]

Originally Posted by theclaw

(I just needed an excuse to replay my exhaust clip)

I did enjoy that.

Regarding 80 SC. Once the O2/Lambda system is even partially understood, there is absolutely no reason to remove it. In fact, it will waste gas if you do.

As Roger says, do some searches on CIS setup and member psalt recommends setting the CO a touch rich, but not so rich the 02 system can't throttle back the AF mixture to stioch at idle and when cruising. At WOT the 02 system disables and your car is like the earlier SCs w/o O2.

In 81 there is a WOT enrichment circuit that your 80 does not have. I don't fully understand the difference between the 80 vs. 81 at WOT because of this circuit but perhaps Porsche found they were leaving some power on the table?

Keep in mind these cars at 180hp are not fire breathers. Just do some reading and get it set up right and you will still have plenty of fun.

[Swiftmotoring]

Strange result when I disconnected the O2 sensor today. The surging disappeared completely. It normally takes 2 hits on the key to fire the motor, it now fires on hit one. I did notice a much "richer" smell around the car....too be expected I suppose. I disconnected the sensor with the motor off, tomorrow I will disconnect with the motor running and see if there is any change in RPM's. All I can say is it was very nice to drive around today without any of the surging that has been present over the last few years....!