So I've been getting CEL error code P0420 for about 8 months now, on my 96 f150 4.9L. I finally have some extra cash, and would like to take care of it, (and maybe boost my mileage a bit, but no high hopes for that...)

If I were to just replace the cats, and leave the rest of the system the same, can I use any of these, like the magnaflow?
Catalytic Converter - 1996 Ford F-150 | O'Reilly Auto Parts
I want to say I've read that one of the cats on these trucks is just hollow, so does that mean it is likely not the culprit of the error code and can be left there? which one is that? According to magnaflow's website, the replacement front and back are both filled with catalyst?
I know the 93190 is the direct fit one with the pipes, but it is also much more expensive and I have a friend who's a mechanic, and he will weld in the new cat, so is there any need to buy the direct fit one?

And then, if I wanted to replace my entire exhaust system with say a flowmaster muffler or a magnaflow muffler, should I just cut out the entire exhaust system then have him weld in new piping to get to the muffler, rather than buying an entire cat-back system?

Thanks

 

Save up and swap it all out at once...do the magnaflow cat for sure, grab a flowmaster or whatever you like and get some good pipe welded up and you will be set!!!
Matt

 

If you don't have emissions tests where you are you could simply buy(or make) an O2 eliminator and replace the rear cat with straight pipe. $4.50 DIY O2 Sensor MIL Eliminators

 

we do have emissions testing.
my only question is, with error code P0420, or a bad cat, should just replacing the cat fix it, or is it likely a new one will stop working as well? the truck runs perfectly fine, and there have been no other error codes triggered in the last year.

So too sum everything up, I can replace the front cat, cut out the back one, weld in new piping to a muffler and I'm set? or should I leave the rear one in, and cut behind that to weld in piping to a muffler?

 

Have you already checked that the downstream O2 sensor(s) are working normally?