p0140 Need help desperately

[oosterveld]

So when I bought the car about a two months ago the cel was on and came up with p0140 which is the o2 sensor and po660. The VICS one I can deal with later but my tags have expired and I live in a county that requires emissions. I replaced the the downstream o2 sensor and cleared the cel, but it comes back on after about 25 miles. The car does also have a 3 inch exhaust and looking over paperwork for the previous owner it looks like he took it to the dealer for this issue and they brushed it off and simply states "with aftermarket exhaust code will likely never go away. I have also tried the spark plug non fouler on the o2 sensor method but that does not work either. I don't know if its related but the car did have an air fuel tuner spliced into the ecu which is now disconnected, but the cel was still showing those codes both now and while it was still installed. Could the wires from the ecu being cut or not connected properly be causing this? I'm really at a loss as this prevents the car from being legal and is my only form of transportation so any help is greatly appreciated.

 

[hornsfan10609]

I have the non-fouler trick on the secondary O2 and it has never thrown a code in the 4 years I've had it. Do you have both non-foulers stacked together?

 

[oosterveld]

yes I stacked both of them, but the code still remained even after I replaced it and tried without the non foulers at first. I guess I'll take a multimeter to the socket to see if it's even getting power or anything, any other ideas?