Volvo 240 high NO results during smog test Tech says maybe bad CAT

I own a 1993 Volvo 240 2.4 with 200K miles on it, and overall in good running condition. I consistently have problems with high NOx. Last year after I did a distilled water decarbonizing, tech said it was so close to passing he knew how to "blow it out" by engine acceleration in park prior to test and it passed. This year new tech. Finally passed 15/50 test with Nox reading of 917ppm allowed-970, but failed nox in 25/25 with Nox reading ppm-1255 allowed-878 test. New tech thought the earlier tests got it "hot enough" to make the 15/50 test pass? With the CO reading of .09% in the fail Nox test it appears the Catalytic converter is working, just too lean, otherwise the CO would be much higher? Cat needs CO to "reduce"? NOX.? Any suggestions? My guess your Cali. standards are more stringent than Ga. and so your computer review program may not be able to make recommendations with your $20 review? Or do you know of a similar service that is available in Ga. Fuel pressure regulator? Thanks for any suggestions.

Answer:

Original CAT or aftermarket? That's is the question. If you have not yet replaced this Volvo's Catalytic Converter you probably want to do it now. To play it say see if you can get a smog check station (or emissions test center) to conduct a CAT intrusive test (this is the test where they take an exhaust sample from before and after the CAT , and compare results). Since your Volve is not equipped with an EGR valve, Nox reduction is completely left to the CAT. The CAT will wear down. Now, if the intrusive test shows the CAT is good, you'll need to start looking into lean fuel problems... vacuum leaks are number one, then move into fuel management problems.

posted by SmogTips Support