Help! Catalytic? Sensor? or something else?

[medtrust]

Not long after buying my 03 expedtion 5.4 started missing and running crappy on the low end. I was told by someone he saw something like fireballs fly out of my exaust as I was climbing mountain so, I had a tune up with plugs, boots and such... The expy started running better but still sounded like crap (exaust wise).
Well now I have replaced the engine (swapped) due to spark plug blowing out of head damage and high mileage 196K.
Anyway mechanic told me I need to have cats replaced but I'm not spending 2K for factory crap. Has 4 of em' and O2 sensors behind. I don't have to worry bout emissions here but I dont want the eng. light to come on either. And it still causing some crappy running on bottom end.
I have heard about dummy sensors, and after market cats but want to verify if this will work.
Any suggestions?
Thanks for any and all help.

 

[walnuts4x4]

I know some programmers with custom tunes can be written to avoid the CEL... not 100% but pretty certain... I know the 03s can run the SCT programmer and I believe 5 star tuning can make custom ones... others will chime in or might wanna google "custom tuned programmers" for your year

 

[rburch]

You could replace the cats yourself for 1/4 the price!

 

[toms89]

I just have two high flow cats in my custom exhaust set up. The tuner has rear 02 sensors turned off in my tune but they are installed. The front 02's are used by the ecu to tune. Rears are to check emissions performance only and not required to run properly but you will likely get CEL if they are active with no converters.

 

[medtrust]

Thanks all for the help, I check into the tuners and doing it myself.

 

[dougmcp]

You can get around the cost of tuners if you just install O2 extenders on the rear O2 sensors.