How hard to change the cats on 96 3.8l

I have been driving for several months with an expired inspection sticker because of a CEL on. I think I have fixed the P0401 that was causing the light. Replaced DPFE,EGR.Cleaned EGR ports in lower intake, replaced whole engine vac harness (they were all breaking due to age).
But now I am getting a P0420 code with no CEL on. The CATs have never been replaced. I need to keep from spending too much more on this car since it has 180k mikes on it. The car has always run well despite the codes.
I am thinking of replaceing the CAT(s). If I can do it my self, it would be preferable. The Haynes manual says to take it to a shop, but I am a DIY when ever possible.

Thank You for any advice.

Hi,

I know Wiswind changed his. As you may know, you buy the whole Y pipe with both Cats on it. Rockauto has it at $350. I don't think the job is a snap, but is do-able. I'm sure Wiswind will chime in, but in the meanwhile you could search his posts.

I did it to my 96. It was a pain but it wasn't too bad. I don't know why the manual says that. There are plenty of other things in the manual that are alot harder to repair. You will need to use plenty of penetrating oil but make sure to have all the oil gone before you start it as penetrating oil is very flammable. The last time I had to remove it one of the studs on the rear manifold broke so be carefull of that. You can't drill and tap it while it's on the motor and removing and reinstalling it was a BIG pain.

Not that bad. I had to drop mine to do the motors lower end. Use a LOT of lube on the manafold studs!!!! Snapping a stud on the rear manafold will take it from a dooable job to a REAL PITA!!!!!!!!!!!!!!!!!!!!

I will have to wait to look at the CATs . Now I have a problem with a P0174 (lean) condition and rough idle when cold.

FIRST thing to think about is if they need replaced.
I replaced mine due to ratting...........my replacements are makeing some rattleing noise....a different sound......but still a sound.
I am certain that my original OEM units had broken ceramic internals....which is why I replaced them.

In the case of a rattle, I would FIRST determine that the heat shields are not loose.
FORD had a TSB about that......and.....I read it.
The solution to broken weld joint(s) on the heat shields.......is giant hose clamps.......so....instead of FORD's.....I went to the plumbing section of my local hardware store....and got those big oversized hose clamps that are for the big piipes.....and used them.

In my case......it was internal....but well worth checking.

If the catalytic conveters are NOT woriking.....you WILL get a CEL with a catalyst inefficiency code.
You have 4 oxygen sensor.....2......which are called "downstream" sensors have only 1 mission is life......monitor the catalytic coverters to make sure that they are doing their job.
In other words....if they are not working......the OBDII system WILL tell you ( and the 1995 windstar is OBDII compliant)

If the internals are not rattling to heck.....and you don't have a catylist inefficienty code.....you are BEST off leaving the OEM units in place.

The BEST replacemtent would be a OEM unit......with Walker a cheap man's (that would be me) 2nd choice.