Hi there, I'm getting pretty terrible gas mileage and am going to try changing out my o2 sensors, but i need to know how many are there, and where are they located? I've been seeing answers of ranging from 1-3. It's a 2001 XLT 3.0L

Thanks for the help!

 

Depends if its flex fuel or not I have 4 on my 03 flex fuel and i think the regular has 3 it has to at least have two you should be able two see them all from the bottom look right after the manifolds then before and after the cats.

 

On a "V6" engine there should be 1 O2 sensor on each exhaust manifold.
Bank 1 sensor 1
Bank 2 sensor 1

Then on OBD II vehicles(after 1995) there will be 1 O2 sensor after the catalytic converter(sometimes 2), this sensor is mainly for monitoring if the cat converter is working well enough, i.e. cleaning up the exhaust, these often last the life of the vehicle since they get "cleaner" exhaust.
Bank 1 sensor 2

The Bank 1 sensor 1 and Bank 2 sensor 1 O2's are used to fine tune lean/rich condition.
Then the average between these 2 sensors is compared to Bank 1 sensor 2 to see if cat converter is working to lower emissions, so the back O2 sensor has some effect on lean/rich but not much.

O2 sensors are rated for 80,000 miles but often work fine much longer.
Burning oil or long term "running rich" will shorten an O2 sensors life.
Since there are two O2 sensors monitoring lean/rich, if one was causing a false lean, so computer was running one Bank richer you would probably get a CEL(check engine light).
You can use a live OBD II scanner to monitor the sensors.


The MAF sensor is what tells the computer the volume and temperature of the in coming air, this sets the gross lean/rich, so would effect MPG more than O2s.
MAF sensors are easy to clean, but use MAF sensor cleaner not carb cleaner.

EGR system issues can effect MPG as well, but you would usually get a CEL if that's the case.


The returnless fuel system you have runs at 65psi of pressure, so even a small leak will cause a change in MPG.
You can rent fuel pressure testers that hook up to the fuel rail.
Start engine make sure pressure is approx. 65psi, then shut engine off and watch the pressure, it shouldn't steadily drop, it should hold.

At the end of the fuel rail is a pressure damper with a vacuum line attached, engine off, remove that vacuum line and smell it for gas smell, if you smell gas then replace damper.


Cold weather means denser air, which means more fuel is needed to get correct fuel/air mix, so lower MPG in winter is not abnormal but it is not a big change.
Also in colder climates gasoline often gets ethanol added to prevent freezing, ethanol does not have the same "energy" per gallon as gasoline, it has less, so MPG will go down, but again not much.
But combine these two things together and you may notice the difference.

 

Had problem finding locations. Your previous answers on where location of 02 Sensors helped. Mine runs on regular, and O'Reillys told me it had only one sensor. Found 3 on it. Changed out the two upstream that come off of each exhaust manifold with Bosh 02 Sensors. And changed the one that is past the Catholic Converter with a Walker downstream 02 Sensor. The ranger had 250,000 miles on it with the original factory sensors. It was throwing a code that showed problem was with 02 Sensors. And had a check engine light. After changing Sensors it runs good without a miss, and has no check engine light showing up. Your explanation in your previous message helped me to understand what sensors I needed.

 

Good work, and thanks for post your fix

 

Found it much easier to remove them without ruining threads to apply a good penetrating oil to base of sensor's, and let it soak in for a couple of days prior to removal. Makes the job much easier without ruining existing threads.