Black smoke from exhaust
Black smoke = excess fuel. Causes range from a clogged air filter to faulty injectors.
Black smoke is unburnt or partially burnt fuel — the mixture is too rich. For petrol engines this is often brief (on acceleration) and signals over-enrichment. For diesel, it's classic injector or DPF regeneration trouble.
Petrol: clogged air filter, faulty MAF (under-reporting airflow), leaking injectors, bad MAP sensor. Diesel: worn or dirty common-rail injectors, excess boost, failed DPF regeneration.
OBD-II: LTFT sharply negative (ECU cutting fuel), P0172/P0175 (system rich). For diesel — P2002 (DPF blockage), P0088 (rail pressure too high). Check MAF PID — is airflow under-reported?
First diagnostic steps
- Inspect and replace the air filter
- Read LTFT: if negative −15% or more — ECU is cutting fuel (system too rich)
- Check MAF g/s against spec for the engine displacement
- For diesel — check live Common Rail pressure PID
- Perform an injector return flow test
Likely fault codes
Click a code for detailed description, causes, and diagnostic plan.