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Black smoke

Black smoke = too much fuel or not enough air. Diagnose sensors, boost leaks, and injectors.

MED RISK

Common symptoms

  • Sooty exhaust
  • Poor mpg
  • Lack of power
  • DPF/EGR warnings (diesel)

Cost expectations

DIY: £0–£80. Garage: £120–£500+.

Note: prices vary by car and region. Use this as a planning range.

Most likely causes (ranked)

  1. Air restriction — Dirty filter, collapsed intake.
  2. Boost leak / underboost — Less air than expected.
  3. MAF/MAP reading wrong — ECU overfuels.
  4. Injector fault — Stuck/leaking injector.
  5. DPF/EGR issues (diesel) — Combustion efficiency reduced.

Quick checks (fast, low-cost)

  • Check air filter/intake for blockage.
  • Inspect boost hoses and intercooler connections.
  • Scan fuel trims / airflow readings.
  • If diesel, check DPF pressure and EGR codes.
  • If fuel smell is strong, investigate injector leak.

Recommended tools

These tools make diagnosis faster and stop you buying random parts.

Related fixes

If your symptoms don’t match perfectly, check these next.

UnderboostDPF / EGR problemsPoor fuel economy

What to do next

  • Fix air/boost first.
  • If diesel, avoid repeated short trips until resolved.
  • Injector faults can damage DPF/cat if ignored.

AutoSolveHub helps you narrow possibilities. Always confirm critical repairs with proper testing and safe procedures.