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Failed Smog Test

1992 Geo Prizm Failed For High NO and Ignition Timing

Hi. We have a 1992 Geo Prizm. We changed the spark plugs, replaced the oil & filter, and put in a new car battery. We went to get the car smogged & it failed due to "oxides of nitrogen" and "ignition timing". My question is, if we filled the car with a higher octane, drove it for about 100 miles would this take care of any carbon build up? Any feedback would be greatly appreciated. Thank you kindly, Mom & daughter ~ Kim


Ignition timing will need to be corrected first and your Geo Prizm given a second smog test. Incorrect ignition timing alone, can cause high NO emissions.

If this Geo Prizm is a California emissions certified GSI model it will also be equipped with an EGR valve; which if not function properly can increase NO as well.

Using higher octane gas will not remove carbon build-up. Follow the link below to learn more about NOx failure.

What causes high NOx?

posted by SmogTips Support 05-02-2016 02:16 PM
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