cause of excess hydrocarbons in cars exhaust?

Answer 1

Mixture too rich, bad oxygen sensor, bad catalytic converter.

Answer 2

Emissions 101

HC = Hydrocarbons. Where your car is concerned, this is unburned fuel. It is fuel that went into the engine and right back out again. Never got the match, never burned. Causes can be very dirty oil, need for a tune-up, vacuum leak, oxygen sensor failure, bad spark-plug wire, mechanical problems in the engine, ignition timing etc.

CO = Carbon monoxide. This is fuel that went into the engine and got lit up, but went out before the burn was complete. Causes can be a dirty air filter, excessive fuel pressure, poor compression, oxygen sensor failure, ignition timing, engine temperature, etc.

NOx = Oxides of Nitrogen. Caused by very high combustion temperatures (> 2500 deg) and pressure. This is normal in an efficient engine performing well.There are devices on the engine and in the exhaust to reduce these emissions.

To determine the cause of your excessive HC, diagnostics are in order. If you cannot perform them yourself, or don't know about PATTERN FAILURES concerning your car, then your options are two ---
1) Pay for the diagnostics (Perhaps expensive, but efficient)
2) Start throwing parts at the car, and hope you hit the problem with one of them. (Inefficient and potentially very expensive)
Additionally, without a smog machine, you won't know how well you have done in correcting the problem.

Good Luck

Answer 3

HC is unburned fuel from incomplete combustion. check for poss weak spark, failed coil or wires, air/fuel mix, clogged air filter and egr problems.

Answer 4

Running rich or ignition missfire, worn valve guides/seals, worn piston rings, failed catalytic converter etc. etc. etc.

Answer 5

incomlplete combustion.