Because most heavily modified engines are noiser than stock engines, the knock sensor detects false knock. Some people wrap the knock sensor in a rag or something or move it to a quieter place, but if you know you have a good tune and use good gas then you don't really need it.
98.5 SVT
91 Escort GT (almost sold)
96 ATX Zetec (i brake to watch you swerve)
FS: SVT rear sway bar
WTB: Very cheap beater
CEG Dragon Run - October 13-15