o2 sensor question

[chris_2.5gt]

Hey guys just got a 97 legacy 2.5gt and I am getting horrible mileage. I get about 93 miles to half a tank. I tried running without the air filter, got brand new tires for winter and still no difference. So what I am thinking is maybe one or both of the o2 sensors are finished. I know there is a way to tell with a volt meter but what I was wondering about was the lifespan of an o2 sensor and if they would look a certain way if dead or dying?
I also have no CEL, and any suggestions on other possibilities would be good as well.
Thanks,
Chris

[LSiTo5Revo]

Do you drive the car with the pedal to the floor all the time? i noticed when i did my mileage was TERRIBLE. How often do you run fuel treatment through the system? Lucas is what i run and i def see a difference in it. out of curiosity what octane are you running?

[chris_2.5gt]

I wot sometimes but most often I drive slow to try and keep the consumption down. I have given it 1 fuel treatment in the last month. I run regular gas, should I be running super? I plan on changing to a neon ignition with the later wires as well as changing the spark plugs, I also have an exhaust leak between the midpipe and the muffler because the flanges have completed rusted around the bolt holes for all 4 holes. I made a custom gasket out of sheet metal to hold it together for the time being and will be getting either a wrx or sti muffler and then will just have to change the midpipe. Will the wrx or sti midpipe fit? I heard they are too short for the BD?

[anothernord]

I wot sometimes but most often I drive slow to try and keep the consumption down. I have given it 1 fuel treatment in the last month. I run regular gas, should I be running super? I plan on changing to a neon ignition with the later wires as well as changing the spark plugs, I also have an exhaust leak between the midpipe and the muffler because the flanges have completed rusted around the bolt holes for all 4 holes. I made a custom gasket out of sheet metal to hold it together for the time being and will be getting either a wrx or sti muffler and then will just have to change the midpipe. Will the wrx or sti midpipe fit? I heard they are too short for the BD?

If you think your O2 sensors are going out, replace only the front first, since its the one that the ECU actually uses to determine air-fuel ratios.

[LSiTo5Revo]

they require that you run 93 in the 2.5's. my legacy has the CEL on. I hooked it to the scan tool and pulled knock snsr, first o2, and evap flow. but thats only because my evap cant be hooked up. doesnt help you any but may be something that's causing it to send that code out.

[Brockley]

just curious; who runs 93 octane?

[anothernord]

just curious; who runs 93 octane?

If they sold it here I would.

[Huffer]

they require that you run 93 in the 2.5's. my legacy has the CEL on. I hooked it to the scan tool and pulled knock snsr, first o2, and evap flow. but thats only because my evap cant be hooked up. doesnt help you any but may be something that's causing it to send that code out.

What continent are you on?
In the US, the recommend fuel for a stock 2.5L normally aspirated Legacy from 97-09 is 87 Octane unless pinging/knock occurs (usually at higher elevations) in which case you can switch to 89.

[jey]

Just to add information in 1996 the premium was recommended for the 2.5L.

In run 93, but only certain stations carry it here. But I'm also running 6 psi of boost.

Sorry folks, I had to clean up the personal attacks on this topic - we need to stay on topic, and if you have something useful to say there is no need to back it up with attacks.