94gsrcivic

ok, here we go, my buddy is having problems with his 98 civic with a d16y8. hes gone through 3 oxygen sensors, every time his check engine light comes on it tells us that there is a slow signal from the O2 sensor. this wouldnt be such a problem if Vtech didnt shut off every time. the only thing that he has ever done to the O2 sensor previously is a DC Header and an Air Fuel Ratio guage...please let me know if this is normal and if anything can be done to preven this. thanks.