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94 Geo Prizm, Nox emissions out of limit

11-19-2005, 03:11 PM
Recently my 94 Geo Prizm was inspected for emissions and failed because the Nox level was 2120, twice the acceptable limit. The catalytic converter appears to working well enough with no loss of power; though the MPG, which has been very steady, did decrease over the past several tank fills. The Haynes Auto repair for Corolla and Geo Prizm also associates EGR problems with this symptom (some detonation rattling). Their pictures and description show an EGR system, which is the stricter California arrangement. These components are not installed on my Geo and the vacuum diagram on the hood does not include an EGR circuit either. The diagnostic code read on the dash check engine light shows nothing visually; just a normal steady blinking light.

Does anyone have any suggestions to correct this excess Nox? In the mean time it’s back to the basics…

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