Mechanics

Black Smoke From Exhaust Pipe

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Step by step repair guide on how to repair black smoke from the engine exhaust system. This article pertains to most non hybrid vehicles.

Difficulty Scale: 3 of 10

Tools and Supplies Needed

  • Fuel pressure gauge
  • Protective eyewear and clothing
  • Flashlight
  • Engine scanner
Begin with the car on level ground parking brake set.

Step 1 - If the check engine light has illuminated the PCM has detected a malfunction that could be causing the problem. Visit - Scan trouble codes

Step 2 - Inspect under the hood for vacuum leaks which can cause the computer to malfunction. Visit - Checking vacuum leaks

Step 3 - The fuel pressure regulator can cause raw fuel to enter the engine. Visit - Check fuel pressure regulator

Step 4 - A stuck or shorted fuel injector can allow too much fuel into the engine. Visit - Fuel injector test

Step 5 - An air intake boot is designed to transfer air from the mass air flow sensor to the throttle bore. The PCM monitors this air flow and corrects fuel injector signal input. When an air intake boot fails it causes the PCM to respond by inputting more fuel than is necessary. Visit - Air intake boot replacement

Preventive Maintenance

When a tune up is performed the spark plug insulator can inform on a lean or rich mixture. Brownish grey is the desired color and confirms proper mixture while black and sooty means the mixture is too rich and white to light grey confirms a lean mixture. Fuel injection systems rely on pressurized fuel to operate. Visit - Replace spark plugs

Maintaining this pressure is mandatory for the system to function properly. Replace your fuel filter with every tune up to keep your injection system operating properly. Visit - Fuel filter replacement

Helpful Information

Black smoke is caused when the mix of fuel and air inside the engine becomes un-balanced. Normal mixture is 14.5 parts air to1 part fuel. When the fuel to air mixtures change because of a malfunction the mixture can go as high as 14.5 to 2 or 3, two to three times the proper amount. The black smoke seen from the tail pipe is the excess fuel generated from the rich mixture. Malfunctions in fuel delivery or a leaking fuel pressure regulator will cause black smoke to be produced. The fuel injection system atomizes fuel by pushing it through a small nozzle of the fuel injector while under pressure. The computer system measures vacuum and air flow into the engine intake manifold to determine a proper amount of fuel that should be released. Airflow is controlled by the throttle body or throttle valve actuator (throttle) as fuel is distributed directly in each cylinder. The process of measuring the amount of fuel a fuel injector is dispersing is determined by the PCM (powertrain control module - computer).

Best Practices

  • Use quality test equipment to ensure proper diagnosis

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2014-10-23)