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Forum > Failed Smog Test > Question

1979 Chevy Monte Carlo failed to due to high NO (NOx).

replaced egr valve, had intake manifold remove & cleaned of carbon where EGR valve goes, timing adjusted & carburetor rebuilt. When retested the NO's were even higher than original tested. What could be the problem? Why are the NO's still high? Thanks
Answer:

Since you've already replaced your Chevy Monte Carlo's EGR valve, and cleaned the intake manifold passages, we can also suggest two things to further diagnose and if need repair: 1. You should ensure there is manifold vacuum reaching your Chevy Monte Carlos's EGR valve and that the vacuum is sufficient enough to open the valve as needed. 2. Check that your Chevy Monte Carlo is not running lean. If you've check the manifold vacuum and it's strong enough to open the EGR valve and reduce NO, then the problem is a lean fuel condition. Have a smog check repair station using the smog machine as a 5 gas analyzer fine tune your Monte Carlo's carburetor. Also check your smog check VIR, if CO is lower then average, you definitely have a lean fuel air mixture. posted by SmogTips Support

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