since cats and o2 sensors have been a popular topic lately and since I have started hearing that familiar cat rattle combined with 44 and 45 codes (OBD I on a '95) I am at a point where I must replace my cats. The resonator in the tail muffler is rattling a bit too. Since I live in a state with no emissions testing I'm thinking about losing the cats completely and having a custom exhaust fab'd. Stock manifold into straight flow downpipe into tail muffler.

Has anyone done this and if so, what effects have you found?

 

I havent done it but I say go for it........ Im not lucky enough to live in a non emission state

 

I had to do the opposite, put cats back on, I bought mine with the cats cut out and the rest old stock. I didn't notice any power loss putting a high flow cat and flowmaster style muffler. its acctually quieter than the swiss chesse stock exhaust. I would say you won't see much difference powerwise, its a matter of how you want it to sound. you stilll have the o2s either way.

 

yes, new 02's will be installed... just looking to eliminate cats but I don't want to alter / decrease the backpressure too much.

 

I too have been seriously thinking about this, but I have rear O2's so I would need to find the dummy O2's first.
Let us know if you get any more power/mpg when done.
There are headers out there for these trucks if that helps.

 

i had mine taken out and had a local muffler shop install some "test cats". straight pipes (well, not so straight) in place of the cats which plugged up. my timing was off for almost a year and killed 'em. oh well. 200 bucks later and my truck sounds a little more throaty, has a little more power and fuel economy. its not huge, but every little bit helps. im happy i did it. now i dont have to worry about it. i did new o2 sensors at the same time along with new 8mm wires and plugs, cap, rotor, etc. definitely woke up the truck. hills i couldnt climb on the highway without slowing down a bunch now seem like flat roads. cats? I like to think so, the loss of backpressure is not that huge, still has two mufflers to go through.

 

First of all, I will take the DiscoMike approach and say it is totally illegal. Testing or not. Secondly, if you can't bypass the O2's (you can't) it will get funny readings and overfuel.

get some aftermarket highflow cats and weld them in. I have Magnaflows and like them. I paid $250 for them installed.

 

This thread shows that there must be alot of difference year by year, even country by country. My 97 only has front O2 sensors; the wire coming from behind each cat is a thermo - a temp sensor. They look completely different to the o2 sensors at the front. They are a fairly solid looking wire with a sprialled outer sleeve; these are what triggers the dashboard light when there is an over heat. On that basis ripping the cats out ??shouldnt?? affect the engine management as the the thermos dont act like the 02 sensors.

 

Rear O2's on any car do nothing more than tell the ECU that the cats are working or not, thats all.
No rear O2 codes and no problems.
Remove cats and you need to trick the ECU to thinking they are still there.

 

please keep in mind the 95 NAS only has 2 o2 sensors upstream from the cats. these can be installed into any exhaust config (with or without cats). as far as illegal...well i'll leave that topic up those who never speed, ALWAYS make a complete stop at intersections and believe cats are somehow saving the planet....after all, you did buy one of the most fuel hungry trucks on the planet. gotta love 13 mpg