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1997 Oldsmobile Aurora 4.0 Northstar failed smog test for high HC.

My car won't pass the HC at 15MPH 47PPM is max and my reading is 67PPM this is the reason I'm failing the smog test. I use 91 octane fuel Chevron. The technician said I have no computer codes and all systems are working fine. I passed the HC at 25MPH 31PPM max and I have a reading of 27PPM. O2 reading 15MPH 0.0% and 25MPH 0.1%. CO reading max 15MPH 0.46% my reading 0.07% 25MPH 0.43%max and my reading 0.02%. NO 400PPM max at 15MPH my reading is 41PPM and at 25MPH 687max and my reading is 30PPM. C02 reading 14.7 at 15MPH and 25MPH and RPM's were 1628 at 15 MPH and 1214 at 25MPH Any suggestions the car is running perfect. I changed the engine oil before the test. The air filter is clean. Thank you for the help. I'm at a loss and so was the technician who tested the car. He thought the HC level required for this vehicle were too stringent.
Answer:

Assuming all your Oldsmobile Aurora's emission systems are function properly (particularly the ignition system, i.e. sparkplugs, sparkplug wires, coil) it might be time to change the catalytic converter. The Bureau of Automotive Repairs actually disallows replacement of the CAT until all other emissions components have been inspected and no faults found, or found and repaired, and a vehicle still produces high emissions. The Catalytic Converter, commonly referred to as the CAT is a component designed to continue the combustion process within itself and emit a more thoroughly burned and less harmful emission containing exhaust. A good CAT should dramatically reduce HC, CO and NOx. The CAT is a catalyst, it plays a very small part on how well your engine runs and it only begins working after slightly rich exhaust has exited the engine's combustion chambers. The most accurate way to find out if your Oldsmobile's CAT is working properly is by using an exhaust gas analyzer (smog machine). You should visit a local smog station and have the smog technician inspect the CAT with their smog machine. posted by SmogTips Support

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