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Two possibilities come to mind, strictly theoretical since I don't work as a mechanic, I am an engineer: 1. Running too rich. This lowers the combustion temperature which keeps NOX low but the unburned hydrocarbons and incomplete combustion result in high HC and CO emission. Check O2 sensor, airflow/airmass sensor, computer codes, injectors, etc. 2. An alternative theory is that the catalyst is no longer effective, or perhaps if it has air injection, the air pump is no longer doing its job - the catalyst cannot burn off the pollutants because there is no oxygen available in the exhaust stream or the material is no longer usable.

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โˆ™ 2007-07-12 19:06:50
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Q: Why would a 1992 Accord EX fail an emissions test with high hc CO2 but pass the nox in the 40 kmhr test?
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