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1997 Honda Civic HX - 219,000 miles - Fail smog check for high NOx.

my car failed smog - NO (ppm) 15 mph - max = 487; ave =57; meas=741 (fail) ; 25 mph - max = 774; ave = 50; meas = 773 - went to smog repair shop for diagnosis tech said he is unable to do diagnosis on the dyne due to low response from upper oxygen sensor. told me to replace oxygen sensor, which i did. he ran it again on the dyno, then he said he still can't get a reading, told me to fill car up with gas and add the gum out fuel additive. after which drive and make sure it runs close to empty then refill with gas. after which i can go to shop and have it retested. pls help, i need second opinion on this.
Answer:

Your Honda Civic is probably non-EGR valve equipped, and the bulk of NOx reduction is handled by the Catalytic Convertor. We recommend three things. 1. Insure the CAT is not defective. A CAT intrusive test will verify this. 2. Insure your Honda is not running lean. 3. Insure you do not have a high compression problem. The gum out is good to clean carbon deposits from the combustion chambers but it will not work with one tankfull. In fact if carbon build-up is severe, it will not help at all. A de-carbonization process might be required, and should be conducted only by a smog check repair station. posted by SmogTips Support

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