o2 sensor - 89 240sx

[kerv]

Hi, I am noticing that my car is getting worse and worse gas milage every week.  I just had a recent tune-up so I don't think that could be the problem.  I have heard that it could be my o2 sensor.  How do I check if it is good still?  Is this an easy thing to change yourself?

Thanks,

Kev

[whateverjames]

the 89 should have one o2 sensor, right on the exhaust manifold. it's pretty easy to get to and costs $17. i don't know the answers to your other questions though.