which o2 sensor do i put the antifouler plugs on and how many
 

which o2 sensor do i put the antifouler plugs on and how many?i have one on the intake manifold and right after the cat.

One should go on the exhaust manifold- not the intake

i meant exhaust not intake.what about the 2nd o2 on the cat?

IMHO the most important one to put the extender on is the one between the engine and cat, as far as I know, its not a bad idea to put the one on the post cat sensor as well.

i agree if you put one upstream, that sensor will send one signal, and the sensor downstream(after the cat) will expect a certain change. unless you have identical setups on both sensors, then it will more than likely throw a code.

I remember reading somewhere that they shouldn't be used on the downstream sensors, but don't remember where I read it so I have nothing to back that up. I can't even remember what the reason for that was. I have heard of people using one per sensor and have also heard of people using two per sensor to move the sensor further out of the exhaust stream.