Having issues passing SMOG. All the numbers are good except NOX at 15 MPH max is 539 im at 736. Nox at 25 mph max is 792 im at 127. other 15mph measurements are Co2 14.6, o2 .3, HC 10, and CO .02. I know NOX is high combustion temps I triple checked all vacuum lines. Any other ideas before I buy a new cat?
Was the engine fully warmed up at its normal 210 temp? Running too low of a temperature thermostat or having let the engine cool off before running the tests can cause it to fail.
Draws in excess air Especially at lower rpm and lower exhaust pressure and the cat happily combusts the nitrogen in the exhaust with the excess oxygen that came in with the drawn in air
You gotta fix the exhaust leak to get the oxides of nitrogen back down
Because until you remove the excess oxygen coming in with the leak you won't pass
Don't buy a new cat your cat is working fine fix the hole or crack in your exhaust
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