So my 2000 Maxima has failed emissions 3 times now.
The readings were:

Roller test(40km/h)
HC Limit: 65, Reading: 56 Pass
CO Limit: .34, Reading: .64 Fail
NOx Limit: 425, Reading: 29 Pass

I changed the front bank primary o2 sensor before the test(had a code for it).
After the test I got a Bank 1, Bank 2 too lean. Changed the MAF which I was suspecting was faulty for quite a while before(but got no codes). The car drives much better, no more cold start hesitation, idle is smooth(it would have slight mis-fires sometimes), and no pinging.
The readings were more or less the same though on the rolling test:
HC Limit: 65, Reading: 50 Pass
CO Limit: .34, Reading: .62 Fail
NOx Limit: 425, Reading: 39 Pass
They were lower than before at idle, but it had passed idle the first time anyway.

CO basically means it's running rich or incomplete combustion.
Anyone got any suggestions on what it could be? The coils are fine AFAIK, I replaced 1 of them a while back and I'm not getting any mis-fires or codes.
I cleaned the air filter, checked the 3 plugs on the front bank and they look fine, I will change all of them, but I doubt it will make a difference on the test.

 

Maybe a bad cat?

 

Is your max completely stock?

 

I was thinking that too, but it usually fails on other readings too when the cat is bad.

 

Yes

 

Hard to tell. Maybe you got some leaking injectors? Have you had bad mpg?

 

Your results are way off from what they should be. Our state stoped doing actual readings years ago, but I pulled out an Inspection Report from 2002. At that time my 2000 I30 readings were HC 0.0, CO 0.0, and NO 1.0.

Surprised you are not currently showing any codes. Sorry can't be more helpful.

 

It's not very hard to throw the readings off.. I used to do emission testing for a living, the readings aren't really that high.

 

Doubt it. The fuel consumption is still pretty good.
At this point I'm leaning towards low compression on one or more cyl or a bad catalytic converter.
I'm gonna change the plugs and do a compression test tomorrow.

 

are you using any fuel injector cleaner or stuff like that? Anychance there is coolant leaking in?

 

I am losing a bit of coolant. Where does it usually leak in?
I've never used injector cleaner, but I doubt it would help with the emission readings

 

Leaking coolant? I would do a compression check on your motor.

 

I have heard (experts chime in here) that fuel injector cleaners actually hurt the chance of passing emissions. Not that it matters if you dont use it. anyone out there answer my curiousity?