I've heard that the oxygen sensors need to be replaced at about 100,000 and can hurt gas mileage about 30%... is this true?

 

i did mine at 85k when i did my exhaust and it helped a little bit

 

How many would I need and about how much do they run? I have about 126k on the car

 

If you replace them all it would be a total of 4. You can get the oem sensor from like autozone for about 50 to 60 a pop. So your looking at about 200 maybe a little more in all of the sensors.

 

30% is a stretch, new ones will help though. You should see a bit of improvment if you do all 4 at the same time.

 

I would not use the crapy bosh ones they sell at autozone, period. Use only Motorcraft for the O2 sensors.

 

If you have longtubes and have the rear ones turned off with MIL eliminators, do your still need to replace those too?

 

nope. It's not even giving a reading.

 

i used my old ones though so it atleast looked good with the o2s

 

I would go with directfordparts.com, I got both the pre-cat o2's for roughly 120 and some change shipped to my house. These are oem o2 sensors, I agree with shizzle, don't get the cheap ones, get the oem's, there worth sixty a piece. GL

https://mustangforums.com/forum/6-cy...2-sensors.html