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Engine & running faults

Black smoke from a diesel exhaust

Black smoke is unburnt fuel. On a modern diesel with a DPF it usually also means extra soot heading into the filter.

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Symptoms drivers describe

  • Visible black smoke under acceleration
  • Loss of power or limp mode
  • Poor fuel economy
  • DPF light appearing more often

Possible causes

  • EGR valve stuck open or heavily sooted
  • Injector wear or leakage
  • Boost problems from a faulty turbo or actuator
  • A restricted air filter or intake leak
  • Air-mass or pressure sensor readings out of range

What you can do

  • Do not keep driving hard — it loads the DPF further
  • Note whether it smokes cold, hot or only under load
  • Have it diagnosed before the DPF becomes the bigger bill

How we check it in the workshop

We compare live fuelling, air-mass and boost data against expected values, test injector performance where supported and inspect the EGR and intake.

Is it safe to keep driving?

Book it in soon. Over-fuelling wastes fuel and shortens DPF life.

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Related repairs

How we can help

Diesel DiagnosticsModern diesels combine high-pressure fuelling, turbocharging, exhaust gas recirculation and after-treatment. When one part of that system drifts, the symptoms usually show up somewhere else.Read more EGR Valve Repair & ReplacementThe EGR system recirculates a measured amount of exhaust gas back into the engine. When it sticks, everything downstream suffers — including the DPF.Read more Injector Diagnostics & Injector-Related RepairsInjector faults imitate a lot of other problems. Testing the injector data before replacing anything avoids fitting expensive parts the engine did not need.Read more DPF DiagnosticsA DPF warning is the end of a chain of events, not the start. Finding out why the filter is loading up is the part that saves money.Read more

Engine & running faults

Other symptoms in this group

Car stuck in limp modeLimp mode is a protection strategy, not a fault in itself. The control unit has seen a reading it does not trust and has reduced power to keep things safe.Read more White smoke from the exhaustColour, smell and whether the smoke clears once warm are what separate normal condensation from a coolant or fuelling problem.Read more Blue smoke from the exhaustBlue smoke points at oil reaching the combustion chamber or exhaust. When it appears — start-up, overrun or under boost — narrows the cause.Read more Car losing power when acceleratingLoss of power is either a fuelling, air or protection issue. Live data under load is what separates them rather than guesswork.Read more Car cutting out while drivingIntermittent cut-outs are among the most important faults to record properly, because the evidence disappears the moment the engine restarts.Read more Car overheating or temperature gauge risingOverheating is one of the few faults where what you do in the next few minutes decides whether it stays a small repair.Read more

Want this looked at properly?

Send us your registration and describe the symptoms — we will tell you what the next step is.

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