ok so the problem is i need to replace all 4 o2 sensors on my car to get it to pass smog.i have already replaced 2 sensors wit the red pigtails on it, the ones closest to the cat converter. now i am lookin for the 2 wit the black pigtails, or closest to the engine block.ive been under the car and cant see them or through the hood and still cant spot them...i need help folks.please if you hav detailed information or even pics would b the best. thanks