Hi!

I have a 1999 ford ranger with the 3.0L. All stock, really.
Recently my fuel economy has been shit, like 16mpg mostly highway, and a couple months ago I got a check engine code for an O2 sensor. I only very recently found out WHICH O2 sensor (left bank upstream) and replaced it two days ago. Too early to say how my fuel economy may or may not have improved! But will see when I've burned through this tank.

The old O2 sensor had a nice white and orange film over its steel shroud.
I checked the sparkplugs, too, they were just a little white and still in good shape though I replaced them anyway. They had spots of blue and purple around the threads from heat.

So my question is, any thoughts on what made it go bad?
And, should I consider replacing my 2 other O2 sensors? Just because this one got bad enough to trip the check engine light, the others could be on their way out...

As a friend told me, can I try just cleaning the sensor off with a bristle brush and some acetone? Test it with a volt meter and a torch to get it hot enough. and see that it falls in parameters?

It was also suggested by the guy at the parts store, to try cleaning the fuel injectors, that the white could mean it's running lean and the injectors are clogged?

thanks for the advice!