OK I got a new cat thanks to StrangeRanger, it's one cat that will be replacing both of my cats and will be installed in the pre-cat location, stock my o2 sensor is between the 2 cats and I have 2 other's on each exhaust manifold, my new cat has a bung hole (lol) for an o2 sensors but it is on the inlet pipe, so since I’m only having one cat now do I locate the o2 sensors before the cat or after it between the cat and muffler?

 

The O2 (HEGO) should always be before the cat and as close the manifold or header as possible. It must be hot to function properly, hence closer the better and before cat so it will sniff what's coming from the engine, not catalized emissions.

The only systems that I am aware of with after cat o2's are the newer systems like on my 2002 mustang and I'm sure the newer trucks. It has four total O2's, a pair before and a pair after, that's what requires a mil eliminator to use an offroad pipe, because if you remove the cats, your ECU will "know" they are missing.

I'm not sure what you are talking about in your manifolds, as far as I know in 96 the only change was the air injection tubes were piped directly into the manifolds instead of into the heads. Never seen any O2's in manifolds on our trucks.

 

In '96 Ford switch to the OBD-II computer system so I have a total of 3 o2's. One on each exhaust manifold and one between the cats.
I know of of plenty of people who run with no cat's on there newer F150's and don't have any computer problems like a CEL so I’m not worried of that, just not sure how it may effect the performance of where it's located.

 

The third HEGO sensor on a 96 does not control the EFI like the upstream sensors, it monitors cat function. It has to go AFTER the cat so it can measure how well the cat is cleaning up your exhaust. If you put it in front you'll get all sorts of ugly codes puking out of your check engine light.

On mine the third sensor is located about 3" behind the cat outlet and located at about 30° from vertical angled towards the centerline of the truck

 

Ah ha, you guys do have the sniffer O2!!!

I didn't realize that crap started in 96, I stand corrected StrangeRanger, thanks for the "edumacation", LOL.

So there is a single post cat O2 on the trucks since they only have single exit exhaust, right.

I wonder if you could use a mil eliminator on that single one like on mustangs, it seems to be doing the same thing (the post cat HEGO).

 

OK so I'll put it after.....thanks for the help.

 

Ok another quick question StrangeRanger. I was thinking I could just use my old tubing after the pre-cat to utilize the stock o2 port but the pipe between the cat's look's like it's 3", the catco is 2.5" so I guess I'll just have to find some new tubing. It would be nice to use the stock tube after the cat because of the o2 and also the shape of the stock tubing because it's curved for that tranny cross member.

 

Just weld a new bung on the 2.5" tube. It'll be less work by the time you're done trying to make the old part fit.

 

ok, plus I'd like to look under there and see all new pipes

thanks