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What could cause high HC emissions on a 93 Mazda Protege that failed the last three smog checks in a row?
Hsugiyama
Elevated hydrocarbon (HC) emissions usually indicate ignition misfire due to fouled spark plugs or a bad plug. But high HC emissions can also be caused by burned exhaust valves (check compression), lean misfire (check for vacuum leaks, low fuel pressure or dirty injectors), or rich fuel conditions (fuel saturated carburetor floats, excessive fuel pressure, leaky injectors or a dead O2 sensor). An extremely lean condition will only cause HC to rise abnormally Elevated HC readings during acceleration indicate ignition misfire under load. The causes could be: Defective knock sensor; Weak ignition coil(s); Excessive resistance in spark plug wires; Arcing inside the distributor cap; Worn, fouled or incorrectly gapped spark plugs; Over-advanced ignition timing; or Lean air/fuel mixture. High HC emissions are caused by only one thing, incomplete combustion, this could be due to an engine misfire, an intake air system leak, a burned valve or low cylinder compression on any of the cylinders.
What this means is that the engine is not burning all of the fuel in the combustion chamber and expels most of the fuel out of the tailpipe without converting it into CO, which means there is a problem with one or more of the cylinders.
It could be simply a bad spark plug or spark plug wire or a loss of engine compression in one or more of the cylinders, I recommend having the basic engine functions checked for a misfire condition
Wiki User
∙ 16y ago
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