This will depend on the age of the vehicle. Older carburetor fueled vehicles have needle adjustments to control the fuel air mix. Newer vehicles are computer controlled, and may need the computer codes checked for an issue.
It is the car running too rich. or the car is using more gas than air.
Your car is running too rich.
If a car is running too rich, the air to fuel mixture is not right. Running rich means that there is too much fuel (gas) going into the engine for the amount of air going in. On the opposite side, too lean would mean that there is not enough fuel going in for the amount of air. Cars can run rich when the oxygen sensors go bad, or on older cars, if the carburetor is not adjusted properly. Running rich can be accompanied by a distinct exhaust smell, and in the extreme cases, some blue smoke. The inside of the exhaust pipe will be black if a car has run rich for any amount of time (when it's cool, take a light colored rag and wipe it inside the end of the tailpipe-if it comes out black, the car is probably running rich).
Engine oil could be running too rich or rings!
14.7:1 --- Air : Fuel Ratio. perfect. not lean, not rich.
It is more than likely running rich. The Check Engine Light should be on if that is the case. Have the ECU scanned.
it sense oxygen come out from your engine to tell the PCM your car is running rich or Lean
Your civic could be running too rich because you used bad gasoline. It could also be running rich if a spark plug needs replaced.
if your car is running rich, then you need to either get your ecu tuned to adjust it. Or get a controller like a SAVC or Hondata. For a performance motor like an h22 a properley dyno tuned ecu makes all the difference.
It all depends if the car is running lean or rich, if its burning oil, if its burning coolant. a clean running car doesn't really have a strong smell. By the way, exhaust fumes are toxic. It contains carbon monoxide and it is highly toxic. So don't go around smelling car smoke.
if the spark plugs are black because your car is running too rich. your plugs are fouled.
If the fuel is running too rich in a car, it would be a good idea to adjust the EFI or Electronic Fuel Injector (carburetor). It would also be a good idea to make sure that all of the air cleaners and oxygen sensors are clean and functioning properly.