Oxygen sensors, probably a dumb question

[mustangphil]

So how do I know if I need them and what improvement can I expect after changing them? I got 145K on the car, changed them once but only because they came with used BBK catted h-pipe that I got on ebay. I cleaned them once as well with a wire brush and it seemed like it made the engine light go away for about 2 years. Thanks in advanve for all help.
Phil

 

[vristang]

After 2yrs the O2s are probably getting out of whack.

I think manuals suggest changing them every 60k miles?

You should see better fuel economy, and possible better part throttle response.

 

[srothfuss]

Yup every 60K miles. There is a ingredient in gasoline that deteriorates the performance of the 02's over time. I think it's Zinc, but I'll have to look it up