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Honda Civic 250,000 Miles Failed High NO

I've tried passing this car for smog multiple times and it always fails due to high NOx. I've replaced the plugs, checked the cat and the honeycombs look fine, and threw in a new radiator to lower the engine temp but still no luck. Also checked for exhaust leaks and I can't visibly see anything. Looking for the cheapest way to get the car to pass, since it doesn't hold much value. Any thoughts?

Answer:

We'd suggest checking cylinder compression to ensure your engine doesn't have heavy carbon build-up which could cause the engine to run hot; causing high NOx. Also make sure the engine is not running lean. If your smog test results indicated 0.00 CO levels, chances are the engine is running lean. Look at the oxygen sensor first for proper operation, and than the remaining emission sensors... mainly the MAP and TPS. This Honda Civic more than likely doesn't have an EGR valve, so that's one component you need not worry about. If it did however, it would be our first selection of emission components to test. On EGR valve equipped vehicles, the EGR valve is primarily used to control NOx. Non-EGR equipped vehicles rely on proper fuel control, engine temperature, and catalytic converter function. posted by SmogTips Support

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