My 2002 Series II (105,000 miles) has never had the oxygen sensors replaced. My fuel economy is terrible these days. After I replace the ignition wires are the oxygen sensors a good thing to replace at this point? Is there a point when you know they need replacing?

 

Plugs and wires, do an induction cleaning, clean the t/body, a can of B&G 44K in the tank and yes 4 new 02 sensors, consider buying them while on sale at Atlantic British.
What octane gas are you running?

 

They need to be replaced when you notice a huge reduction in MPG and you have replaced the plugs and wires but still have a major MPG drop.
So yes, go ahead and replace them.
As long as your tire pressure is good, air filter is clean and you dont have a Fridgedair strapped to the roof.

 

Great thanks I saw them on sale so I figured I might as well get them. So there are 4 of them, thanks.