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1997 Jeep Wrangler Failed Smog Check for High CO and HC.

My 1997 Jeep Wrangler failed emissions for high Hydrocarbons, and high Carbon Monoxide. I have installed a new Catalytic Converter and Oxygen Sensors as well as the Gas Cap (all of these PASSED on the inspection. Could the failure to pass emissions be attributed to the quality of gas I'm using? This Jeep has been parked for prolonged periods of time and perhaps needs a good hard running and better gasoline grade (91 octane for example). Any suggestions very much appreciated.

Answer:

The gasoline grade will not help pass your Jeep Wrangler pass the smog test, but fresh fuel might depending on exactly how old the fuel during the smog test was. If older than 2 months we recommend re-testing with fresh fuel. With that said if fresh fuel does not get your Jeep to pass and since you mention having already replaced the catalytic converter and oxygen sensors (and we'll assume the job was done properly) we have to recommend going back to square one with a hands-on diagnosis. The combination of high CO and high HC usually indicates a air/fuel control problem. Depending on how high CO is in comparison to HC we can determine whether the fault may be with the ignition system or fuel control system. Higher CO than HC emissions usually indicates a rich fuel mixture and would suggest inspecting all emission sensors which control fuel, such as the oxygen sensor(s), engine coolant temperature sensor, and mass air flow sensor. Read more about smog check failures here. posted by SmogTips Support

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