So I failed California emissions for High Nox. They also dinged me for visual on the downpipe. I passed this 2-years ago so I was surprised. I read through the forum as I always do whenever the FD needs some attention and I hit on that I was likely running lean. Looking at the O2 levels below from when I had high NO vs low NO that seems reasonable. Oddly I had the fuel injectors cleaned after the test 2-years ago so thought I would be less lean. Emissions tech advised me to put the pre-cat on to pass the test. I will need to put it on now that I have been dinged for it but not sure that is the issue with the Nox failure.

My question is why might I run lean on OEM computer and fuel setup? Anything I can do with a stock setup to run richer?

Thanks!

Mods:
99 Twins
Pettit Racing 3" downpipe

Changes to fuel system since 2019 emissions test
New fuel filter
New Fuel pulsation damper
Fuel injectors cleaned

Aug 6th, 2021
Test CO2 O2 HC CO NO
Max NA NA 88 0.52 704
15mph 12.2 4.43 63 0.0 841*
25mph 12.2 4.5 42 0.0 327

Sept 2019
Test CO2 O2 HC CO NO
Max NA NA 88 0.52 704
15mph 14.8 0.5 78 0.01 285
25mph 14.8 0.5 50 0.01 296

 

I would think it is running rich. Was it thoroughly warmed up for the test? Just curious.
California is such a pain. If I lived there I would have a whole stock setup including precats.

 

If I were you I would just find someone and pay the 300 to 500 bucks for a hot smog. It's only every 2 years.

 

Thanks for the replies. I was going off of these threads when guessing that I am lean. What's the best way to tell if I am rich or lean?

https://www.rx7club.com/2nd-generati...gh-nox-916766/

https://www.rx7club.com/3rd-generati...ssions-327316/

https://www.rx7club.com/2nd-generati...oxide-1079224/

I don't mind paying but this seems fixable.

 

Testrun, I forgot to answer your question. I did try to get it hot. I drove 25 minutes to get to the test shop and left it idling when I was checking in. The tech had other customer but pulled it on the dyno and left it idling while doing the other car.

 

i would try a new 02 sensor. Nox's change very fast, so it does not take much for that number to come way up

 

the HC and CO went down, and nox went up. pretty easy to see that its leaner.

 

My O2 sensor has 1100-1200 miles on it but is a Bosch. Should I be using OEM or is there another brand to consider?

 

ND is the OE, NTK is good too

 

When I replaced my O2 sensor, I used a generic Bosch O2 sensor (Bosch # 11027). It worked fine.

Link to related thread:
https://www.rx7club.com/3rd-generati...hrottle+plates

 

Tps could be out of range. Have you done a coolant flush or anything on the vehicle? Running a bit hot can also cause high NOX results

 

​​​​​​The coolant has not been flushed since I bought the car but it was drained and refilled 1100 miles ago. I have not noticed the water temp rising but could be. TPS was adjusted around the same time but I will check it. Couldn't hurt.
Current plan was replace FPR, O2, clean EGR, plugs/wires and oil change. Adding a flush and TPS adjust couldn't hurt.

​​​​​What about lower temperature thermostat and fan switch?

 

skip cleaning the EGR, its not on during the test (and even if it was it does f-all). unless it needs plugs/wires and an oil change anyways, these won't change your numbers at all.

 

Checked the TPS adjustment today.
3F = 0.8V closed and 4.95V WOT
3G = 0.32V closed and 4.16 WOT

It slightly out of range. I decided to adjust even though it was close because I was in there. And of course there is a stripped screw. So off comes the throttle body and out to the stores hunting the right bolt. If anyone is interested its M4x0.7 13 mm long. I found 12mm long and used it.

After getting it back together, I adjusted slightly and had everything in range.
3F = 1.03V closed and 4.94V WOT
3G = 0.41V closed and 4.21 WOT

 

Are you sure that the EGR is not on during the test. During the 15mph test my RPM was 1810 and for 25mph test RPM was 2820.
F125 chart has engine speed above 1700 rpm as EGR gas supplied.

 

the hole in the EGR gasket is like 1mm, it does nothing.

 

Reporting back. I passed emissions test. But not by much; only 1 ppm on NO.

The pre-Cat was reinstalled and TPS was adjusted (barely). The O2 sensor I ordered was supposed to have the correct wire for RX7 but did not. I will send it back and get another. Decided to retest anyway because I had the appointment.

Aug 20th, 2021
Test CO2 O2 HC CO NO
Max NA NA 88 0.52 704
15mph 15.24 0.35 54 0.01 703*
25mph 15.03 0.60 40 0.01 382

It appears that I am still running lean and will look into that some more. Thanks for all of the suggestions.