Engine
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    Why Is Black Smoke Coming From My Exhaust?

    Typical repair cost: $20–$3,500

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    Common Symptoms

    Black sooty smoke
    Smell of raw fuel
    Poor fuel economy
    Loss of power
    Sooty residue on bumper

    Most Likely Causes

    1

    Running rich (gas engine)

    Failed O2 sensor, leaky injector, or bad MAF. Codes P0172/P0175.

    2

    Clogged air filter

    Restricted airflow forces the ECM rich.

    3

    Bad fuel injector (diesel)

    Diesel black smoke usually means an over-fueling injector or bad timing.

    4

    Failing turbo / boost leak

    On diesels — low boost = black smoke under load.

    How a Shop Diagnoses It

    1. 1.Scan for fuel-trim and O2 codes.
    2. 2.Inspect air filter and intake tract.
    3. 3.Diesel: check rail pressure and injector return flow.
    4. 4.Boost-test the intake on turbo engines.

    When to see a professional

    Persistent black smoke wastes fuel and fouls the catalytic converter / DPF — diagnose within a week.

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