1. • Raw fuel is primarily made up of Hydrocarbons (HC).
• Should be almost completely broken apart by the
combustion process.
• If there is a lack of combustion (misfire), some of the
Hydrocarbons pass through unburned and out the
tailpipe.
• Variations in the combustion event (imperfect
combustion) allow HC’s to pass through unburned.
• Catalytic Converter can only deal with a normal
amount of HC’s.

2. • Engine integrity issues (lack of compression, lack
of vacuum).
• Ignition timing.
• Ignition system malfunctions.
• Rich misfires (high fuel pressure, regulator and/or
injector leaks).
• Lean misfires (low fuel pressure, dirty
injector, vacuum leaks).
• Poor fuel vaporization.
• Air Injection system malfunction.
• Excessive EGR.
• Catalytic Converter operation