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Chevrolet Malibu did not pass the smog test due to high HC

My 1999 Chevrolet Malibu failed the smog check because HC was to high. My Malibu's HC was 79 ppm at 15mph and 40ppm at 25mph. Can you tell what could be the problem. Thank you.
Answer:

High HC is typically caused due to defective, worn, and/or damaged ignition components (spark plugs, coils, ignition module, plug wires). However high CO (rich fuel mixture) or low CO (lean fuel mixture) can cause high HC as well. Even if your Malibu passed the CO portion of the smog inspection it may be possible CO is slightly high/low enough to cause a misfire resulting in high HC. A smog check repair station should ensure your Chevy Malibu is in proper fuel control and its Air/Fuel ratio is as close to 14.7:1 as possible. The diagnosis shold begin with inspection of the fuel injection “feedback” system. This test basically makes sure the oxygen sensor(s) is working properly, your Chevy's engine control computer (ECC) is receiving the signals from the oxygen sensor, the computer is computing the data properly and sending the correct signals to the fuel injectors to either increase or decrease fuel delivery. The smog technician must also ensure the ECT (Engine Coolant Temperature Sensor), TPS (Throttle Position Sensor) and MAF (Mass Air Flow Sensor) are functioning correctly as well. These components also control the amount of fuel the ECC commands the injectors to mix with air. Unless your Malibu's CO emissions are below the State's Average (AVE) results, and so long as your Malibu is not suffering from severe misfires, hesitation, or stalling, we recommend diagnosing the fuel control system. Should your Malibu be suffering from any of the conditions mentioned above, go ahead and inspect the ignition system (spark plugs, wires, coils). posted by SmogTips Support

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