this was my reply in another thread just a day or two ago:
Originally Posted by Dgerow12 View Post
Spark plug defoulers?
Spark plug defoulers are adapters that screw onto the spark plug and then screw into the cylinder head. The idea is that it sets the spark plug outside the combustion chamber a bit. If you have bad rings, or bad valve guides your plugs can get fouled from excessive oil accumulation.
They are also the same threads that an O2 sensor uses. By inserting a defouler onto the O2 sensor it pulls the sensor back out of the exhaust stream thereby altering the signal that the sensor sends to the computer.
Many times (but not always) it will alter the signal enough to fool the computer into believing that you have cats when you don't.
At least this is the way it was explained to me................. never tried it myself though.
01 V6 5 spd
Windstar upper, shorty headers, high-flow catted X, American Thunder catback, SCT Tuner, ASP 25% UDP, FRPP T-Lok