The cats on my 1997 4.6L were plugged awhile back so they were removed and the O2 sensors that were in them were eliminated. The wires are just taped up and they've never thrown a check engine light or anything. However, my truck is getting about 12 miles to the gallon and the exhaust smells of gas strongly. I'm kind of thinking this is due to the lack of two oxygen sensors. What do you think?

I see some bungs you can purchase and weld in, but I'm not sure if these are considered the front or rear O2 sensors. Any help would be appreciated!

 

Get the bungs & re-install them, and change your front sensors while your at it. 12yrs old its definitely time for 4 new O2s.

 

Where are the front and rear O2 sensors located? I'm not even sure if the ones I'm missing are fronts or rears. Do you think it will help my gas mileage?

 

primaries should be right at after your exhaust manifold on each side. Yes it will help your mpg out alot! A faulty o2 usually makes the engine run way too rich.

 

Precisely. The rear O2s are down after the catalytic converters, your front ones are up just below the exhaust manifolds in the downpipes.

 

im about to get some new o2 sensors too. anyone know the best quality brand to buy?

 

OEM Bosch ones are fine.

 

I have a 99 f150 4.2 with 168K on the dial. The other day the "Service Engine Light" came on. The code I got was a P0174 bank 2 error code. I have cleaned the MAF and am replacing the plugs and wires. I am also going to replace the o2 sensors. But when I look at replacements, I get 3 different heated ones? Without pulling, is there a factory number to help me with ordering a replacement before pulling? Or does it matter concerning 02 sensors?