97 SE, 112K miles. I've done the CAI, 180 thermostat, TPS tweak, and have the Magnaflow muffler installed. I'm ready to buy my MaganaFlow/Carsound Hi Flow Cat. I've been trying to get smart on exactly which p/n to purchase. What I'm wondering is this:

1) My car has the factory #2 HO2S, is there any advantage or disadvantage to getting a cat without the downstream O2 port, and using an O2 sim/resistor?

B) I'm considering replacing the factory #1 HO2S just because it'* got 112K on it, (though it still seems to be working fine). I know there are some strong opinions and evidence about O2 sensors here, and I've heard too many stories to be confiident one way or the other right now. What I want to know is... since it seems to be working fine, would this help or just be something to thow money at for small benefit. :?

Thanks, Mark.

A shorter high flow CAT from ebay will probably be fine if you don't want to spend big bucks on one and no, you do not need a rear O2. From my understanding, all the rear o2 does is tell the computer you have a working CAT. The o2sim/spoof just sends a "ok" signal the PCM telling it there is a working CAT.

If the rear 02 is bad, it can throw your gas mileage down a little bit. I know from experience though.

there are two O2 sensors, one is behind your manifold, the other behind the cat. The one behind the manifold helps your mileage, while the one behind the cat just makes sure the cat is working.

Are you sure it was the one behind the cat that went bad?

Twister,
A rear O2 will have no effect on mileage. All it does is throw an emissions fault. Your mileage was probably suffering because of a partially clogged Cat.

No, it wasing throwing a code, and I had allready replaced my cat before it went off. It actually started going off right after I had exhaust work done on it. The mechanic said it wasnt reading as fast as it should of, ok to drive it but the car was not functioning up to par like it should.

they are more of a pain in the *** than anything. O2 sensors arnt cheap.

Twister, your mech is dead wrong. The rear O2 has absolutely no effect on vehicle performance whatsoever.

Ok, opinion noted

Not opinion, Twister. Statement of fact. It'* clearly outlined in the FSM'* for OBD2 vehicles. All it does is sniff the exhaust to determine if the Cat is doing it'* job, or if it'* failing and passing nasty emissions to the enviroment.

This O2 will set an emissions fault (and SES light) to warn you of the possible emissions problem.

The front O2 sensor is the one that determines proper AFR and can affect mileage and performance.

If your performance was restored, it was a fluke, or something else done about that same time.