I know it's a stupid question, but I'm really clueless...
 

I know that by running your car without an oxygen sensor, you will waste 30% of your fuel, the car will hesitate, etc. Then why to people run without oxygen sensors?

My SC didn't come from the factory with an 02 sensor. It runs great.

What year car do you own?

I was trying to replacemy O2 sensor the other day and the old connector broke. I haven't noticed the slightest difference. That said, my wrench buddy adjusted teh mixture while I was trying to find a replacement part online so I don't know how much of an adjustment he had to make.

However the plan is to put on a cat bypass (reduced heat mostly) and run the O2 sensor when I fix the connector.

So I too am curious as to the reasons folks would run without one given that they still have the original fuel delivery system (CIS, Motronic,Etc...)

Different fuel systems have different uses for the O2 sensors, so unplugging it on one car may be differently than unplugging it on another car. For example, my 959 does not use an O2 sensor - it gets all the information it needs from the airflow meter and other sensors on the car. Yet, on more modern 911s, you can run into "limp mode" and other problems if you have faulty O2 sensors (plus your car won't pass emissions tests).

In general, it's best to run with the O2 sensor connected as it helps to keep the mixture properly adjusted on most cars.

-Wayne

P.S. There's no such thing as a stupid question here! :)

I have been running my '87 911 with the o2 sensor disconnected for about 3 years now, I only connect when I have the car smogged.

With the sensor connected the car runs much rougher at idle and low speed. It's still drivable but much more smooth without the sensor connected. Now maybe my car has an underlying problem, but for me its better without the o2 sensor.

In the case of the early O2 sensor systems, the sensor only functioned at idle/partial throttle. It was very much a "clever hack" to make sure the car provided good emissions. In reality, a non-O2 CIS should perform the same if tuned properly.

I think the real reason is that its easier to tune off-design with the O2 system not interfering in your attempts to run the system a bit more rich for power.

Of course, in some cars removing the O2 will cause problems because the fuel map is setup specifically to be corrected by the O2 sensor. In this case, the engine will run poorly as its running the safest setting it has.

If the car is tuned right is should proform well without the O2.

CIS cars however can save a fair amount of fuel with the O2 hooked up.

I have mine disconected on my 3.2.

Running it with the 02 sensor causes mine to hesitate. It may not be noticeable to most people as it is very subtle - but it is enough to bother me so I disconnected it.

On the highway I still get 25 mpg. I don't think that the 02 sensor would provide much (if any) improvement.

No O2 on mine for about 17 years. Runs great! And recently when it didn't, it wasn't because of the O2 being disconnectd.

The sensor on my 911SC was disconnected by a previous owner and the car runs great. Passed WA emissions as well, although John Walker had to tweak it a bit.

No O2 sensor in my '86 3.2. Better throttle response, idles better, runs better. I did get a drop in mpg. With the O2 plugged in I got around 22 mpg in mixed driving. Without the O2 sensor I now get 18 mpg in mixed driving. Worth the trade off IMHO.

Al