EZCarFix DIY Auto Repair

Symptom Guide

Black Smoke From Exhaust

Black smoke is unburned fuel. The engine is running rich.

What's happening

Black or dark gray smoke, often with a fuel smell and poor mileage. The engine is getting more fuel than it can burn.

How urgent is it? Medium — schedule the fix

Rich running washes oil off cylinder walls and kills converters. Fix it this month, not this year.

Most likely causes

  1. 1

    Leaking fuel injector

    Drips fuel constantly; often worse at idle.

  2. 2

    Dirty mass airflow sensor

    Over-reports air, computer over-fuels.

  3. 3

    Clogged air filter

    Starves the engine of air; the simplest check.

  4. 4

    Bad fuel pressure regulator

    Too much pressure richens everything.

How to diagnose it — in order

  1. 1

    Check the air filter first; it's the cheapest fix.

  2. 2

    Scan for rich codes and O2 sensor readings.

  3. 3

    Look at fuel trims with a scanner; large negative trims confirm rich running.

  4. 4

    Check for a fuel smell in the oil (leaking injector washing down).

Trouble codes tied to this symptom

P0171 P0174 P0101

If your scanner shows one of these, read its dedicated trouble-code page for the full diagnosis.

Repair guides for this symptom

Repair guide

2019-2024 Chevrolet Silverado 5.3L - Fuel Injector Cleaning DIY

Step-by-step DIY for this repair.

Repair guide

2006-2013 Chevrolet Silverado 2500 HD - Fuel Injector Service

Step-by-step DIY for this repair.

Repair guide

2010-2015 Chevrolet Camaro SS LS3 - Fuel Injector Replacement

Step-by-step DIY for this repair.

Repair guide

2015-2024 Land Rover Discovery Sport S - Replace Fuel Injector

Step-by-step DIY for this repair.

Related symptoms

Check Engine Light Is On Bad Gas Mileage Hesitation When Accelerating

General diagnostic information, not a factory service procedure. If you're unsure, have a qualified technician confirm the diagnosis before buying parts.