My 1994 Celica ST (7A-FE) is now 25 years old so today's emissions test will be the last! Im celebrating with a new exhaust system.

I already got the eBay stainless header, which I plan to have ceramic coated. I would like to use an aftermarket cat.

Should I install the downstream O2 sensor before or after the cat? The guide shows installing it in the downpipe, but in this thread Box (where are you Box?) says to install it after the cat. And what if i don't use a cat?

I also wondered where to get the proper flange for the sensor.



This post has been edited by bryanf: Jul 14, 2024 - 11:08 AM

Down stream goes after the cat, but that depends if you have one or two cats! If you have two cats then you have a total of 3 sensors, which I suspect to be the case since you're worried about the ebay set eliminating one of your cats. You could extend the wiring and have a bung placed after the cat under the center of the car or you could just use a spark plug non fouler to fool the O2 sensor into thinking a cat is present.

I have two sensors and two cats. The first sensor was in the manifold, then the first cat in the bottom of the manifold, then the second (downstream) sensor was in the downpipe, in between the two cats. The second cat was in the tunnel. No sensor after the second cat.

I'd like to try using the non fouler with no cat but that won't work with the flange type O2 sensor. Should I make a sensor extender with a flange? How long should it be?

Would a setup like the howto produce a CEL?

Ok, you could probably just extend the 2nd O2 to after the main cat (tunnel cat) and it would work.

>

I was thinking about doing that! Thanks for the confirmation.



I've finished fitting the header to the head so it's almost ready to take for ceramic coating.

This post has been edited by bryanf: Jul 14, 2024 - 11:06 AM

Please replace that radiator, the top tank should be black not light brown. It's ready to pop.

>
I replaced the radiator, radiator hoses, and thermostat. Thanks for the advice.