97 Leg OBW: O2 Sensor

[Snowman]

Hey everybody,

 

The 97 outback has been getting less than stellar fuel economy recently, and since my mom commutes 60 miles a day, I want to fix this problem. Since I put in new plugs and wires as well as doing a bunch of other PM this last summer, I'm pretty sure that the oxygen sensor is the culprit and needs replacing. It's been in there since we got the car five years ago so I think it's probably getting old and the response time is slowing.

 

I looked on 1stsubaruparts.com and found that they list 2 sensors, it appears to be one before and one after the cat. Do I need to worry about the 2nd sensor at all? I would think that all that one does is tell the computer if the cat is working or not, but I wanted to ask here before ordering a new sensor to see if I need to get both.

 

Your thoughts please.

[JonOfScio]

kelly, first one does all the work. the second just monitors the cat to see if it's working correctly. if it's not inspec it will just default the motor to run lean.

 

it's important to run correctly as well. replace them both if you can manage it.

 

also, our exhaust manifolds tend to crack after alot of use and many miles... like mine has a slight leak, so it's altering the o2 sensor reading, not enough to throw a code, but enough to only be getting 24mpg on a motor that I used to get 30mpg out of!

[Snowman]

Thanks Jon!

 

It's my parents' car, so I'll see if I can convince them to pay for both sensors. I'll also look into the possibility of a manifold crack, which is probably more likely to occur up here with the temperature extremes.