Guest bang847 Posted January 17, 2003 Share Posted January 17, 2003 here is a weird problem... my buddy has an old cadallic seville and it failed smog... the NOX level was in gross polluter status.... but all other gases were very low.. after failing we replaced replaced the EGR valve and the car passes.... the weird thing is that after the EGR replacement the hydrocarbon levels went up by alot! from 12ppm to 107ppm also the CO level went up ten folds too... is there an explanition for this? it is a 86' cadallic seville 4.1L V8 Quote Link to comment Share on other sites More sharing options...
Guest greimann Posted January 17, 2003 Share Posted January 17, 2003 Not weird at all. High NOx and low HC and CO indicate high combustion temps and possible lean mixture. Replacing a faulty EGR introduces exhaust gas into the combustion mix, effectively reducing combustion temps. NOx comes down HC and CO will go up, but still within parameters. Passing smog requires striking the fine balance between too lean and too rich. You just can't tune too lean and expect pass because NOx will be through the roof. Quote Link to comment Share on other sites More sharing options...
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