I know it seems like a stupid question, and quite probably it is, I'm kinda out of it. What I am asking is why do most posts about heated O2 sensors vs. single wire "stock" O2 sensors talk about it heating up from 12V versus from exhaust gas after cranking.

Maybe I totally am not following the way the O2 sensor plays a role in the grand scheme of things, but I was under the impression that the thing just gave input to the ECU to control fuel during closed loop, in other words, light load cruising, in an effort to conserve gas. If this is the case, then the ECU reads the O2 sensor not under WOT, but under partial throttle and leans the mixture to save gas. So when people bring up heated O2 sensors, why is race gas brought into the equation? Running race gas while cruising down the highway doesn't seem like the intended use to me. If you're running race gas, chances are that you're a drag strip and are going to be doing some serious WOT applications. Does the O2 sensor play into this at all? If I am running a Power FC with the O2 Sensor switched off, it's the same thing as having no O2 in the first place, correct? Someone please help me understand this.

My reason for worrying about this is because I have the Escort 3 wire in my car, and it's voltage readings are very low under WOT (supposedly a way to see how rich you are running, but these things are so crappy, I'm starting to realize what a waste of time writing this is). The low voltage readings would point to a lean condition, but after running at the dyno with a wideband O2, I'm actually running rich. It's just annoying to have this 3 wire be giving me bad readings and wonder why I even need to have one in the car. (Gas milage is the only reason I'm aware of)

Richard

 

There are two kinds of 02 sensors, the kind that comes with the car (which may or may not be heated), and a wideband sensor. The stock kind are only accurate at around 14.7:1 A/F- much outside of that range and they can't be trusted. A wideband sensor is accurate typically from 11:0 to 20:1, and includes a circuit that compensates for temperature (stock sensor outputs can change depending on temp, even with the same A/F). A stock sensor is <$100, a wideband one is usually $300, plus $700 or so for the circuit/display. Prices have been coming down though....

Many people tune just using the stock sensors but they really don't know what the real A/F ratio is. When a car is dyno tuned, a wideband sensor is used.

Yes, running with the PFC option turned off is like not having one at all.

If the output from the sensor in your car never gets above .5v and starts switching above and below 0.5v once the car is warmed up, then the sensor is bad and needs to be replaced.

O2 sensors are used for gas mileage, but mainly for emissions reasons.

Race gas doesn't change anything as far as the sensor is concerned. However, a tuner can safely lean out the A/F when using race gas (since it burns cooler than pump gas). This'll create more power.