Joe '87 S4

I just had my car smogged. The results were pretty good except for the NO (PPM) compared to two years ago. What would cause the measurement to get worse in the last two years.

Here are the results two years ago compared to today:

.............Test....CO2%.....O2%.....HC.(PPM).....CO%.........NO.(PPM)
................................................Max...Meas....Max...Meas ...Max...Meas
2005....15.MPH..14.1......2.0.......108......42.....0.71...0.04....767.. ..197
...........25.MPH..14.1......1.7.........83......33.....0.58...0.03....7 06....175

2007....15..MPH.13.5......2.1.......108......37.....0.71...0.03....767.. ..465
...........25..MPH.13.3......2.6.........83......23.....0.58...0.02....7 06....336

The O2% went up a little from last time but the NO doubled from two years ago. I did take the car on a 40 minute drive before the test and the car ran really smooth after the run.


sweanders

IIRC high NO can be due to high combustion temperatures - maybe lower octance gas, vaccum leak or running slightly leaner. But you are far away from any concern IMHO.

Bill51sdr

You've got noooooooo problems, don't sweat it. The O2 reading is just a reference # and is an indication of how efficient the combustion process is. It is not a pass/fail reading.

Joe '87 S4

I always go with premium gas but I think you're right about it running a little lean. The next time I have it over at DEVEK, I'll have them look things over. I'm happy with the 20-year-old's results.

sweanders

Get it dynoed with a 02-sensor up the pipe - that will get you real numbers that you can use for diagnosis in case you think anything is amiss.

Joe '87 S4

That's a good idea. Thanks guys.