Solving Exhaust Gas Failures: High HC
Failure to achieve a pass on HC emissions is usually due to an excessively high ratio of fuel to air, thus causing high levels of unburned HCs. Start by checking the following in the order suggested here.
1: Spark plugs & wires
2: Timing spark/advance
3: Vacuum leaks
4: Other ignition problems
5: 02 Sensor
6: Evaporative fuel system
Plus…Fuel Injection system, Air/fuel mixture adjustment, PCV system, Catalytic converter(s), Throttle position sensor, MAP sensor, MAF sensor, Other sensors/switches, Computer PROM, Internal engine repair, Other repairs/unknown.