1996 chevy blazer 4x4

my code says to change o2 sensor bank1 sensor 1,I was told it's the one
before the converter and I have only 2,but when I was under the vehicle I
see 4 1 before the converter 1 after and one coming from each exhaust
manifold which one is it.
plus I have a slight misfire of the engine during take off, then it will
go away,and sometimes come back, I changed plugs,wires,cap and roter and
that did not do the trick. Any suggestions.thanks

I would change all of them ,cheap insurance.

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85 S-15,Jimmy,2.8 5 speed.
91 S-10 Blazer 4.3 auto.
"fabricationman" <[email protected]> wrote in message
news:[email protected]...
> my code says to change o2 sensor bank1 sensor 1,I was told it's the one
> before the converter and I have only 2,but when I was under the vehicle I
> see 4 1 before the converter 1 after and one coming from each exhaust
> manifold which one is it.
> plus I have a slight misfire of the engine during take off, then it will
> go away,and sometimes come back, I changed plugs,wires,cap and roter and
> that did not do the trick. Any suggestions.thanks
>