Does direction of catalytic converter matter?

[foomanji]

Hi all,

Yesterday I installed a new catalytic converter on my car, but forgot to look at the orientation of the old one before I yanked it off. I put the new one on with (I think) the correct vertical orientation (perforated heat shield up), but I'm not sure about that. Even more importantly, I'm not sure whether it matter which front-to-back direction the converter has? Does it, and if so which way goes forward?

Could someone please glance under their car and let me know:

1. whether the perforated (~1/4") presumably heat-shield/heat-sink should be up or down?

2. which front-to-back orientation the converter has. E.g., point out some bolts that are only on the front or rear side.

Thanks!!!

-Steve

[ShawnM]

If its not clearly marked with an arrow to show the direction of flow or marked with an "A" for inet and "B" for outlet, then the direction really dosent matter. The shield area should face the vehicle though.

[Streetglower]

well if the o2 sensor doesnt reach the hole then its backwards.

[trdcorolla]

there is no o2 sensor on the cat. only before and after the cat on the exhaust pipe in obd2 cars. If I remember right the end with the screen does face the front of the vehicle. The direction of the cat should be important. They are built to flow one way to clean the emissions.

[foomanji]

What do you mean the end with the screen?

Before I put it on, both sides looked the same: about 2" back the honeycomb started.

Yesterday I realized I still had the old cat attached (via a wonderful amount of rusting) to half the old front pipe. The only distinguishing feature I found was two bolts on the front pipe side. I glanced under my car and saw that I have installed the new cat with same two bolts on the front pipe side, so I think I got it right.

[RedAE102]

Sounds like you've figured out that mystery. On the lambda sensors... many OBD-I cars have two of them, my Corolla included. The first resides (conveniently) on top of the exhaust manifold, accessible and visible from above the engine compartment, and the second resides after the warm-up catalytic convertor and before the main cat. Unlike OBD-II though, the ECU never actively checks for the presence of the second sensor; it just assumes that it's there and working when it never gets a signal. I learned this from a friend, who removed his when he installed an exhaust header and cat-back system that doesn't have the second O2 sensor bung, and never had the ECU throw a code.