Service Engine Soon Light, Helllllllpppppp!!!!!!!!

[COBRAon18s]

I just put in an offroad hpipe in my 99 cobra a couple days ago, it works great. I ordered Mil Eliminators from www.mileliminators.com I have 4 o2 sensors but the guys at ramchargers told me i only need the mileliminators on the front two sensors closest to the headers. So i did that and everything went fine. I had no check engine light for 3 full days. Then all of a sudden, i was driving and the check engine light came on. Is it possible i need two more of those elimiators for the back o2 sensors or is it possible that the ones that i put on just work. I made sure all the wiring was done correctly exactly with the diagram and now that stupid yellow light on my dashboard is pissing me off, any suggestions will be very helpful, thanks!!!