Symptoms
- Dark black or sooty smoke from the tailpipe
- Smoke worse under acceleration
- Possible strong gasoline smell
- Reduced fuel economy
- Possible rough idle
Likely causes
- CommonDirty or clogged air filterRestricted airflow throws off the air/fuel ratio toward rich.
- CommonFailing mass airflow (MAF) sensorA dirty or faulty MAF sensor misreports incoming air, causing overfueling.
- PossibleLeaking or stuck-open fuel injectorAn injector that doesn't seal properly dumps extra fuel into the cylinder.
- PossibleFailing oxygen sensorBad feedback to the engine computer can keep the mixture rich.
- Less commonBad fuel pressure regulatorOver-pressurized fuel delivery can flood cylinders with extra fuel.
What to do
- Get the check engine light scanned even if it's not on, since a pending code can point to the cause.
- Check and replace the air filter if it's dirty or clogged.
- Clean the mass airflow sensor with a proper sensor-safe cleaner or have it tested.
- Have a shop check fuel trims to confirm a rich condition and narrow down the cause.
- Have injectors and fuel pressure tested if the simpler fixes don't resolve it.
- Avoid extended driving with heavy black smoke, since it wastes fuel and can foul the catalytic converter.
Tools and parts
- OBD-II code reader
Engine air filterSearch: “engine air filter for [year make model]”
Mass airflow sensor cleanerSearch: “MAF sensor cleaner”
When to call a pro
A shop can read live fuel trim data to confirm the rich condition and its exact source faster than trial and error at home.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.