Ever since I started putting aftermarket exhaust on my car, I've been running into this problem. I had it when I had manifolds, and my old bassani catted x-pipe and mac catted h-pipe, and now with my headers and x-pipe. I know it is the passenger side upstream 02 sensor that is reading slow. I've had Ford replace that sensor twice and it still comes on. I'm running MIL's on the back o2's. My last alternative is to change both front o2 sensors with some quality/performance aftermarket o2's.

Does anyone have this problem? Do any of you guys drive around with the Check Engine Light going, knowing that this is the code and just don't worry about it?

I'm wondering if I'm doing any damage to my cats or the engine it self (maybe running lean or rich). But I guess if that where the case I'd be getting that code too.

The only advice I've gotten from the dealership is to put the stock system back on, but who wants to do that?

 

The 02 sensor code will run your car rich. That's why you need the MIL's. But if your still getting the code then you really should replace your 02's. Long term it'll make your car run like poop...[:'(] Good luck with whatever you do though...

 

I have MIL's on the back two sensors. Has this happened/is happening to anyone? Do I need to buy two new upstream sensors? If so, what brand? Denso, NTK, Bosch. . .?

 

You have long tube headers with 02 extensions? All the wiring is long enough? If you just spliced into it then I recommend buying the extensions. They are MUCH better.