IS200 Exhaust / Catalytic Converters / O2 Sensors / Emissions

[andykao]

The back box on my IS200 has been damaged (it has a few dents here and there - probably the previous owner hit it somehow) and it's leaking. I might also have a leak in the middle section, not sure but i think i can see some gas escaping. I also have a P0420 error code - Catalyst System Efficiency Below Threshold. And also a bad O2 sensor (bank 2 sensor 1 - precat) - already purchased it and it's going to be replaced next week.

The car has almost 400k kms - engine has been rebuilt 20k kms ago and runs fine.

The exhaust is probably the original one, so i'm planning to replace it with a custom made stainless steel one. And now here are my questions :

1) any way to check if the precats are working ok? is the code P0420 for the main cat or the precats (or both)? i believe the chances of them still working properly are small (after almost 20 yrs and 400k kms) but i'd like to test them out first (only if possible).

2) if the precats don't work properly, i'd like to replace the standard exhaust manifold with a decat one - so question is, with the precats removed, will the car still pass emissions?

3) the O2 sensors, how many of them are there? i saw there are 4 of them, 2 just before the precats (checking the AFR) and 2 after the precats. But the 2 after the precats, are they between the precats and the main cat or are they both after the main cat? I saw a picture of an exhaust manifold the Bank 1 Sensor 2 was right after the precat (so before the main cat). And also read somewhere that Bank 2 Sensor 2 is on the Y-Pipe, just after the manifold (but also before the main cat). If that's the case, does it mean there's no sensor to check the operation of the main cat? Or am i missing something here?

4) regarding the main cat, where's that located? is it on the Y-Pipe, where the 2 pipes meet? or is it after the Y-Pipe?

5) the whole exhaust system is as follows : exhaust manifold with 2 precats (6-2) > Y-pipe (2-1) > main cat section > middle silencer section > back box section. Please correct me if i'm wrong.

[scudney]

The p420 code could be a simple blow in the exhaust near the sensor as I had this on my IS200 when I had a stainless steel exhaust fitted(so happened there was a small pin hole near the sensor that caused my eml to come on)

[andykao]

9 hours ago, scudney said:

The p420 code could be a simple blow in the exhaust near the sensor as I had this on my IS200 when I had a stainless steel exhaust fitted(so happened there was a small pin hole near the sensor that caused my eml to come on)

that's probably the best case scenario, there's definitely a leak in my exhaust right under the front seats area (can smell it when the engine starts), so that all makes sense. will head over to the exhaust shop to have it checked out and hopefully welded or fixed without replacing the whole thing...

[scudney]

Good luck and all the best,keep us posted 👍

[andykao]

Still not sure about the O2 sensors and if removing the precats would still allow the car to pass the emissions test...

[scudney]

Did you take it to the garage?and what was the outcome?

[andykao]

didn't take it to the garage yet, will do that tomorrow, but i've asked around and no one seems to know exactly where the 2nd row of o2 sensors are placed exactly - after the precats or after the main cat...

[eddiea1]

On 12/4/2019 at 8:40 PM, andykao said:

didn't take it to the garage yet, will do that tomorrow, but i've asked around and no one seems to know exactly where the 2nd row of o2 sensors are placed exactly - after the precats or after the main cat...

 

These pages from the repair manual cound be of help

https://1drv.ms/b/s!Agw5WaqnlFk9g7ob6hxKT8g6VTV4zg?e=JlEKNf

 

https://1drv.ms/b/s!Agw5WaqnlFk9g7kNyYvYuGu1Hsam1w?e=zRm5I6

[andykao]

18 hours ago, eddiea1 said:

 

These pages from the repair manual cound be of help

https://1drv.ms/b/s!Agw5WaqnlFk9g7ob6hxKT8g6VTV4zg?e=JlEKNf

 

https://1drv.ms/b/s!Agw5WaqnlFk9g7kNyYvYuGu1Hsam1w?e=zRm5I6

found these but i thought i they might be wrong... but since you confirm...

i see all 4 o2 sensors are before the main cat, so there's nothing to check the operation of the main cat... so strange...

so it seems the car relies mostly on the precats? or what's the deal here?