Interesting Emission Test Results

I have had my 1990 since 2010, the first time I had it to be inspected at 175K I put some plugs in it. They put it on the rollers for the emission test.
High Speed
CO Std 1.33 Reading 0.14 Pass
NOx Std 1512 Reading 1449 Pass

Low Speed
CO Std 1.20 Reading 0.17 Pass
NOx Std 1657 Reading 1635 Pass

I was like whew!!! Barely squeeked by!

2011 178K went to same place, only thing new was did timing belt, water pump, and fuel filter. Though they did not put on the rollers so I thought whew again as I was concerned that I was so close that last time I would not be surprised to not pass
High Speed
CO Std 1.20 Reading 0.09 Pass
NOx Std N/A Reading N/A

Low Speed
CO Std 1.20 Reading 0.17 Pass
NOx Std N/A Reading N/A

Ok so here we are in 2012, again went to same place, 182K and again was put on the rollers, only prep I did was put a full tank of Shell premium fuel.

High Speed
CO Std 1.33 Reading 0.16 Pass
NOx Std 1512 Reading 1274 Pass

Low Speed
CO Std 1.20 Reading 0.16 Pass
NOx Std 1657 Reading 1292 Pass

Wow, I was pleased to see the numbers were so much better, makes little sense to me, but could it have been the fuel?

Quote:

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Originally Posted by Yeller90

IWow, I was pleased to see the numbers were so much better, makes little sense to me, but could it have been the fuel?

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Was the car 'hotter' this year, or did you jump in and drive to the inspection station? (You'll typically get better emission results if you drive the snot out of it and then go get it inspected)

I believe it was pretty much the same the same weatherwise each year (August), and I drove it about 3 miles to the station each time with no hotdogging, just made sure the car was up to temp.

If you did thi in the last week the air temp is 10-15*f cooler than last year which means lower NOx

Looked up the temperatures on the days I got the inspections, the 2010 and 2012 were nearly identical temperatures 90 degrees, 2011 it was over 100