My inspection is up this month. I have replaced:

O2 sensors, MAF Sensor, and installed a new Cat. My car failed the NOx sniffer test. Limit is ~800 and my car was reading ~1300.

The Cat was brand new, and I was told to drive it for a week and come back. I am concerned it will still not pass and wanted suggestions on how to get it fixed or get around this issue....

Car is a 95 SC300.

 

How long had you changed the park lugs, rotor, cap rotor? Had fuel injection been service?.. remember air filter is important
Hope this help

 

In addition, make sure you have driven it for at least an hour before you test it, preferably on the highway where the cat can get hot. Also check your PCV valve and make sure it is clean...relatively cheap piece to replace under $5 USD.

 

Fuel injection has not been serviced. plugs, rotor, cap, wires were replaced 1 month ago.

PCV valve was replaced also

The mechanic did mention the cat needed to heat up and we sat in the parking lot revving it for 30 minutes. That brought the NOx reading down, but not enough to pass.

 

wow... my car, all original 14 years old, passes with almost 0 reading across the board when warm, and only read 25-35 when cold...

what modifications (if any) do you have???

 

There are no mods. Everything is stock. The previous owner cut the cat out, but I installed a new one, so I would think it would be fine... Guess I will drive it for a week and take it back in hopes the cat needed broken in...

 

cats don't need broken in... we've replaced one and literally smog tested it within 30 minutes of install and it's worked...

did you replace all of the o2 sensors?

is there a check engine light at all?

might be worth getting it scanned to look at the fuel trims and see whats up...

it definitely wouldn't hurt to clear the ECU and drive, maybe there was some bad gas or something at some point in time that has caused the fuel trims to be skewed...

in 95, our cars had a almost obd-2 system, meaning all the sensors were in place, just not the software...

 

Is there anything I can add to the fuel to lower the emissions? I am already running 93octane.

 

Could the timing being off be causing this?

 

most definitely...

 

There are some high end scanners and computer programs (w/cable), would figure a good enough mechanic would have one that could check out the O2 sensors, some of those computer programs can even check a lot of other variables.

 

We do diagnostic work at my shop here. Even the most experienced guys, with the best tools, still go back to basics, and pull wiring schematics and put voltmeters directly on the sensors. Resolution in the ECU is never as good, and faulty wiring can play a part as well...