Ok - I have a 04 Edd. Bauer 5.4 expedition. Looking for better fuel economy like everybody else is. I have a open intake, free low exhaust and looking at 2 other options. Electric fans how much do they really help on mpg. and I keep hearing different stories on removing the cats. I heard form diff. people that removing the cats will improve the performance a great deal, but I also heard it will improve and will not improve the mpg. If I put in the dummy o2 sensors it is worth the time to remove the cats. Thanks in advance.

 

On that vehicle, you probably won't see the gains in fuel mileage that you're looking for by removing the cats. You CAN see improved performance numbers, but the gains in economy will be minimal, if any. My brother-in-law calibrates these things for a living and says that on newer Ford vehicles, they tend to richen up with the cats removed...to where they'll make more power...but use more fuel to do so. You're also very likely to set a "Check Engine" light if retaining stock downstream HEGOs, but if the "dummy" ones are employed to send an "all good" reading back to the processor, you may get around that.

Still, in answer to your question...you probably won't notice much, if any improvement in fuel economy with the cats removed...and it can in fact be WORSE than before, although the trade-off being it will make a little more power.

It's your call!