I was getting rid of my old crusty catalytic converter today and was curios about this attachment. It has a rubber hose a few inches after the metal ends and runs up into the body. I know some ceramic catalytic converters used to have air tubes to add oxygen to the catalytic converter for cooling purposes. This one doesn't appear to have an opening. What do you guys think?

I'm guessing it IS an air tube, which would mean it is the wrong cat for these cars, and some joker either picked it up cheap or picked it up planning to do something odd with it. If that tube has been taken up inside the cabin? Seal it up and get rid of it, it could also push exhaust gas & monoxide into the car, a very bad thing.

This kind of thing is why I'm a firm believer in buying the FSM for any car. It will almost always show you what it supposed to be there, and if you have it around it is easier to find out "WFT? That can't be right?"

I have some PDFs of service manuals, but my car is JDM. There are some slight differences I have found when referencing the USDM manuals aside from MAP vs AFM and the steering wheel being on the right.

The tube has a proper grommet and looks to be factory cut. Maybe someone with a JDM market car can chime in. I'll probably trace this thing, since there could be an air pump somewhere.

Still seems odd. "Rule Number One" is that you never mix any part of the exhaust system with the interior of the passenger cabin, because no matter what you do, there's a chance you'll kill someone with the exhaust gasses. Which doesn't make it impossible, just terribly unlikely.

The cat replacement doesn't have the attachment for this, so no worries. If it was part of cooling the old ceramic cat, then I doubt anything would have gotten into the cabin. It should have functioned as a one way system adding air to the cat.

"No chance" is why *no* exhaust line is ever taken into the cabin. Even if there was a one-way valve, or a suction venturi in the line, those devices can and do fail regularly, and the flow can reverse through them.

And that's the problem: There's just no safe way to run an exhaust fitting into the cabin. Even when the exhaust is totally outside the cabin, people manage to get killed by it. If you notice, any time the ignition is "on" even when the engine is off, the fan blows at a low speed. You cannot turn off the fan completely, no matter what you do. This was mandated as a safety requirement (I think in the 70s in the US) to bring in "fresh" air from the base of the windshield because the only way to keep exhaust out, is to pressurize the cabin with fresher air. And again, even with that annoying fan, people still find ways to get monoxide poisoning. Its no fun.

But on the bright side, at least you've got a readymade fitting to hook up a relief tube.<G>

my old jdm car had that, always ran a straight pipe, so it was tucked onto the top of the heatshield. had to have it for the inspection, when the cat was on the car, OE cat had a little air pipe on it and a clip kept in there. no clue what it did, or why we never unplugged it. `

Red wrote:"No chance" is why *no* exhaust line is ever taken into the cabin. Even if there was a one-way valve, or a suction venturi in the line, those devices can and do fail regularly, and the flow can reverse through them.

And that's the problem: There's just no safe way to run an exhaust fitting into the cabin. Even when the exhaust is totally outside the cabin, people manage to get killed by it. If you notice, any time the ignition is "on" even when the engine is off, the fan blows at a low speed. You cannot turn off the fan completely, no matter what you do. This was mandated as a safety requirement (I think in the 70s in the US) to bring in "fresh" air from the base of the windshield because the only way to keep exhaust out, is to pressurize the cabin with fresher air. And again, even with that annoying fan, people still find ways to get monoxide poisoning. Its no fun.

But on the bright side, at least you've got a readymade fitting to hook up a relief tube.<G>

What fan? I have never seen this. I can turn it on or off with the key on ON. Strange.

I may be confusing which cars I'm in but I think ours are already covered by the fan rules. Try something newer. Nice warm car in the winter, you pull over and shut it down to wait for someone, and the car pulls in icy cold air if you've left the key on to listen to the radio, etc. Same thing in the summer, nice cool cabin, but unless you keep the engine running that same fan pulls in the hot air if you've left the key on for the radio.

Of course if it gets new enough, you can shut it down entirely and the radio still runs until the door is opened. Some of the newish Nissans actually have a "power management computer" buried in there now, because there are so many things that don't just turn on and off anymore.

4ag MAP ecus had a provision for exhaust temperature sensor. When the cat was near melting point a light in the japanese cluster will show you a symbol for the converter with heat lights coming off of it. My guess is because there was no EGR or knock sensor on the JDM blue tops, a dummy light is the best they could muster to warn of catastrophic failure

Makes perfect sense. This doesn't appear to have any openings.