Hydrocarbon (HC) is basically raw fuel, otherwise known as gasoline. The
main reasons vehicles fail for high HC is defective spark or ignition
system. Out of the 3 systems your engine relies on to produce combustion
(air intake, fuel delivery, and spark ignition control), the ignition system
has components which require replacement most often. Sparkplugs and spark
wires are constantly exposed to high temperatures and high voltages. You
must ensure your engine's ignition system is working properly by inspecting
all the sparkplugs and sparkwires. If any of the plugs look worn out or have
excessive carbon build-up replace them immediately. You may use any brand of
product designed to work in your vehicle. The distributor cap should also be
inspected for cracks or excessive carbon deposits. If it appears that the
cap may be faulty, you will need to replace it. More then likely you will
see an instant performance increase once these corrections are made, as well
as a decrease in HC.
This is an excerpt from a SmogSmart VIR report, and is not intended to
replace a hands-on diagnosis.
