whats the deal with the oxygen sensors? me and my buddies have been argueing about this for days. my friend in the auto tech class at the trade school we go to swears up and down that you dont need your oxygen sensors and that your engine wont run any different without them. he says all it will do it throw a check engine light.

i was under the impression that an oxygen sensor reads the amount of oxygen in the exhaust to tell the computer if the engine is running lean or rich so that it can compensate for it. but i also read somewhere that if you unplug your oxygen sensor that the computer senses no reading and puts the engine into some sort of safe mode and makes it run rich which is what causes the bad mileage.

ive also heard of people, myself included on my old truck, that has had a bad oxygen sensor and actually gotten better gas mileage than with a working sensor. why is that?

whose right and whose wrong here? does it matter if the engine is speed density or mass air flow? does it differ between ford and chevy? or are all oxygen sensors the same?

 

Tell your friend to stay in school because he still has a LOT of learning to do.


Yes exactly, and I'll add that the O2 sensor is the ONLY feedback device the computer has to tell it how well it's doing it's job.

Right again.

It's because the computer is getting bad info from the sensor and it doesn't know any better.. it's just following the programming it has which is all based around feedback from the O2 sensor.

No.
No.. but don't tell the Chevy guys.. we like to keep them in the dark.
Yes.. mostly. There are two types of sensors a wideband and a narrowband. The narrow is the most common and the type found in a production vehicle, it just switches from a high voltage to a low voltage as it senses A/F ratios passing the stoic ideal of 14.7:1, so it can't tell you how rich or how lean a motor is but that's enough for an EFI computer to make adjustments to bring fueling back towards the ideal. A wideband on the other hand varies it's output voltage smoothly from about 0-5v over a range of A/F raios of about 8:1 to 20:1 so it can tell you exactly what A/F ratio the engine is producing at any given time. This type sensor is typically only used for performance tuning purposes where you want the motor to operate consistently at a slightly rich mixture of around 12-13.5:1 where it will make maximum power and detonation potential is at a minimum.

 

So what happens when you just unplug the sensor? I know the check engine light will come on but what else? I'm about half tempted to unplug mine for a week and drive it just to see what it's like. Maybe I would get better mileage? Then again maybe I'll get worse?

I know my other buddies 4.0 mustang has true duals ran on it and they didn't bother to put the o2 sensors back in it.

 

One other thing. I read on a mustang site that when you unplug them and it runs better that you may have another problem with your fuel. Such as a faulty fuel pressure regulator that isn't allowing the motor to get the right amount of gas it's needed under normal conditions until the computer causes it to run richer

 

But unplugging the ones after cat have no effect on the engine itself just says bad cat right?

 

on some cars with 02 sensors after the cats(maybe all ob2 cars?) you can run the after cat sensor unplugged and it will just throw a code,which you can have shut off by getting the computer programmed.

 

So maybe their talking about the sensors after the cats?

 

Garrett, try being more specific, in the makes, models and years....

 

It wasn't a specific make year and model or I would of lol. It's just the function of the oxygen sensors in general.

The debate was mainly over two 95 f150's, a 97 f150 , and a 99 mustang

 

Keep your forward o2 sensor. It helps the ECM do its job. Now if you have rear o2 sensors...those don't do crap as far as how the engine runs. I have the ones on my race mustang turned off due to the fact it doesn't have cats.