Failed NCT Emssisons - High CO

Pops_20

Hi All. First time failing NCT emissions on my Nissan 180sx. Would appreciate any advice on what's causing this.

Low Idle

CO: 1.32 % Above: 0.50% FAIL

HC 129ppm Above: 0ppm N/A

High Idle

Lambda: 1.00 Not between 0.97 and 1.03 PASS

CO 0.37% Above 0.30 % FAIL

HC 114ppm Above 200ppm PASS

So I am close enough to passing the high idle CO, but not the low idle. Lambda is perfect so it doesn't seem to be a bad O2 sensor or exhaust leak. Could this be solved with dipetane and getting the exhaust very hot before NCT?

prawnsambo

Got this on another forum. Limits are from the UK MOT, so ignore them.

Pops_20

So in my case, would it be correct to say I have CO high, HC low? I don't know about O2 or CO2 as the test doesn't check for those.

In that case, rich mixture?

prawnsambo

https://www.boards.ie/discussion/comment/122169731#Comment_122169731

Yeah. With the proviso that we don't know the other figures.

Possible problem with your MAF or air filter.

Pops_20

Just wondering how can the Lambda value be 1.0 if the car is running rich? Sure the lambda would be off if the high CO is caused by such a rich mixture?

mk7r

This will be a bad cat, the car could only be running rich if there was an exhaust leak after the cars first O2 sensor thst leaked just enough air to make the mixture perfect at the tailpipe, not likely

Pops_20

https://www.boards.ie/discussion/comment/122172361#Comment_122172361

Any tricks to revive the cat? It's been perfect for the last 7 NCTs. What causes it to go bad?

User1998

https://www.boards.ie/discussion/comment/122172370#Comment_122172370

Oil burning destroys them. You’ll probably need a new one. €200 or so