Smog test NOx very high, in So Cal.

[Neuromancer]

88 3.2 Carrera coupe, daily driver, stock, 110,000 miles, seems to be running OK.

Passed smog successfully for 20 years by just warming the car up properly. Then in 2020 I failed HC & CO by a wide margin, NOx barely. After installing new O2 sensor, and new cat I passed easily: 25MPH: CO2 = 15.3, O2 = 0.0, HC = 6, CO = 0.02, NOx = 0

This year failed again, this time with extremely high NO: 25MPH: CO2 = 14, O2 = 1.4, HC = 9, CO = 0, NOx = 1250 (lambda calculated = 1.070)

Changed spark plugs, oil & filter, unconnected/reconnected O2 sensor wire, and verified brown wire connected. Tested again and NOx increased to 1800

Idle is OK, but will stumble occasionally like it has for many years. Remove oil cap and RPMs go down slightly, so there may be a vacuum issue? I've also read about adjusting the AFM for a lean condition, looked at how to do it but didn't feel confident changing it, also don't know if just changing it would resolve the NOx issue. The mechanic I had been using retired 4 years ago. So looking for some help. Located in the 909.

[sparkysvega]

Mine failed on the nox. My mechanic replaced o2 sensor, plugs and richened the mixture quite a bit . He said lean condition causes hi nox . Funny thing , mine passed at the california smog referee the first time easily . 2 years later at standard smog station, I fail with high nox. They really lugged the car down on the dyno , I want to say 3500 lbs . I wonder if that is why, or California decreased the limits to make it harder on old cars? Also the cat I have is a Magnaflow , I think I want to find a stock one for the next smog . Took it to my mechanic and had him take to the smog guy and make necessary adjustments.Thats what in doing from now on .

[DucRS]

I just failed for the same reason 1986 911 150K miles in Cali

From some quick research I found that high NOX is caused by running too lean. Remedy is to decrease the airflow on the Airflow Sensor. My problem is, I can't seem to figure out how accomplish this...Following

[PeteKz]

If you still have the original O2 sensor in the car, it's past time to replace it. That may fix your problem.

[Neuromancer]

bump

I need to get my baby back on the road before the end of May so expanding my search to anywhere in So Cal. Looking for a shop that might be able to deal with this NOx issue. TIA

[FloydPink]

High engine temps can cause high nox too, I believe. My car recently failed with high nox because it sat idling for too long (10/15 minutes) and got too hot before going through the test.

I've heard some pelicans recommend a shop called Black Forest in San Diego, might be worth getting in touch with them. Can't vouch for them personally, I haven't worked with them before.

[proporsche]

I think you are running a little too lean..

Ivan

[proporsche]

I think you are running a little too lean..

Ivan