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Hi All,

2005 hyundai accent at 160,000 miles, new spark plugs and MAF sensor.
I took the car couple times for smog-check but it tailed always with high Noax values.
I also tried C-poam and it did not work either. There is NO engine lights/codes on. Smog guys said it is the Catalytic convertor but I want to make sure that is the problem before replacing it because it will cost $600-$800 since it comes with manifold

Any kind of help appreciated. Thank you.
 

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High NOX comes from high heat lean exhaust temps.. and possibly bum catalyst..

Accent (USA) model does not use EGR for NOX control..

Wanna try and cheat it,,, go get some methanol (race alcohol) and add some to tank.. do not fill up, as mixture for alcohol is around 6:1, where as gasoline is around 14.7:1 for perfect air-fuel ratio.. E85 be easier to get, but is ethanol instead.. just want enough to keep engine running, not so much the engine wont run (too much alcohol).. might tip off the smart emission guy when he see numbers on smog report..

Seems kinda odd they doing tailpipe emissions, thought everybody was plug in OBD, and if readiness tests complete, and no DTC found, PASS,, you got sticker and on your way ??

Make sure engine temps not high either, nothing over 200 degree water temp, not overheating are you ?

Lastly, OX logic in PCM would typically set DTC for weak/dead catalyst, might have dealer do graph of Ox sensor values and see what happening.
 
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