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
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 codesStep 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 regulatorStep 4 - A stuck or shorted fuel injector can allow
too much fuel into the engine.Visit -Fuel injector testStep 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 -
boot replacementPreventive 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
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 replacementHelpful 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).
Use quality test equipment to ensure proper diagnosis
Written by Ken Lavacot 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 2009-07-28 (Updated 2015-01-05)