Check for Diagnostic Trouble Codes
Black Smoke from Engine
Black smoke is caused by too much fuel being processed inside your car's
engine and then released from the tailpipe of your car. Malfunctions in
fuel
delivery or internal system leaks will cause black smoke to come from the tailpipe.
Before fuel injection became available in automobiles in the mid 1980's, the carburetor
was the main fuel and air mixer in most vehicles. A carburetor was a simple device
that supplied the engine with proper fuel to air mixtures. Carburetors performed
two operations 1. meter air flow 2. deliver the correct amount of fuel to air mixture.
This mix could be kept even during the wide range of extra factors associated with
an engine such as high temperature, cold starting, hot starting, idling and acceleration.
The primary difference between a carburetor and a fuel injection system is that
the fuel injection system atomizes fuel by pushing it through a small nozzle under
pressure, while a carburetor utilizes vacuum created by air flow into the intake
manifold. Airflow in an injection engine is controlled by the throttle body; fuel
is distributed directly in each cylinder. This creates better fuel control, lower
emissions and faster acceleration. The process of measuring the amount of fuel a
fuel injector is dispersing
is determined by the PCM (powertrain control module). The fuel injection system
has several parts: the
mass airflow sensor or map sensor,
throttle body,
throttle position
sensor, idle control
valve, fuel pump, fuel pressure
regulator, fuel lines, and oxygen
sensors.
Cause of Black Smoke
Black smoke is caused when the mix of fuel and air 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 is the excess fuel generated from the rich mixture
and can be cause by one of the following:
Troubleshooting Black Smoke for Exhaust
Testing for a Blown Fuel Pressure Regulator Diaphragm
- A fuel pressure pressure by using a diaphragm/spring combination in conjunction
with intake manifold vacuum. When the fuel pressure regulator diaphragm ruptures
it allows raw fuel into the vacuum feed line and then into the intake system of
the engine. This condition creates a rich black smoke from the tail pipe on start
up and while running. To check for this condition remove the vacuum line from the
regulator, if fuel is present in the line the regulator has failed. Some GM (CPI
Injection) are designed with an internal regulator that you must remove the upper
intake manifold to inspect. Most fuel
pressure regulators
are on the fuel rail on top of the engine in plain sight. If you cannot locate your
fuel pressure regulator consult a
repair manual.
Removing the Vacuum Feed Line
Testing Fuel Pressure Regulator - The
fuel pressure
regulator adjusts fuel system pressure depending on the load of the engine.
Vacuum is applied to the fuel pressure regulator to control system pressure. When
the fuel pressure regulator is not functioning properly it causes the fuel pressure
to be above normal operating pressure. This condition causes excess fuel to be injected
into the engine causing a rich mixture that produces black smoke. To test for this
condition (engine off) remove the protective cap and attach the
fuel pressure
gauge.
Attach Fuel Pressure Gauge
Support the fuel pressure gauge for observation, and then turn the key to the
on position. The fuel pressure gauge should jump up to your system pressure. If
you do not know your system fuel pressure consult a
repair manual. Actual
fuel pressure will vary slightly but should be fairly close to specification.
Fuel Pressure Gauge
Then, start the engine, the fuel system pressure should stay the same. While
watching the gauge, snap the throttle, the fuel system pressure should jump up about
5 psi. If the system fuel pressure does not respond the fuel pressure regulator
has failed. If the fuel pressure gauge falls the fuel filter is plugged or the fuel
pump is failing. When testing is complete, remove the fuel pressure gauge feed line
and replace the protective dust cap
Testing a Fuel Pressure Regulator
Check for Fuel Injector Malfunction - When a
fuel injector malfunctions it
can allow excess fuel into the engine. The fuel injector is manufactured with a
control valve that allows fuel to flow at prescribed amounts. If this valve sticks
open it will flood the cylinder with fuel. This excess fuel causes black smoke from
the exhaust system. To test for
this condition the injector fuel rail must be removed and injectors tested. It is
difficult to fully test an injector, but an basic operation test would include pressurized
air and a 12 volt power source.
While an engine is running you should be able to hear the injectors clicking
as the electronic valve opens and closes. To aid in this inspection use a stethoscope
and touch it against each injector. If no audible sound is heard test fuel injector
pulse and supply voltage output (this test is used for most cars). This test will
tell you if the computer system has operating voltage and injector trigger signal.
Remove an electrical connector from a fuel injector (all injectors need to be tested)
probe both sides of the connector with a grounded
test light or multimeter
(voltmeter) (black lead) switched to DC voltage (there are only two terminals).
Have a helper turn the key to the "on" position without cranking the engine and
observe the test light.
The test light should illuminate one side of the connector only and the multimeter
should be at about 12 volts. Next, switch the test light or multimeter (voltmeter)
lead (black) or to the positive side of the battery to test the system ground injector
trigger, probe the side of the connector that did not light up, have a helper crank
the engine over and observe the test light, it should blink on and off or the multimeter
(voltmeter) should bounce from 0 to 12 volts. (Note: if no injector pulse is present
try disconnecting the remainder of injectors and re-test, if a fuel injector is
shorted it can shut down the injector driver causing no injector pulse. If injector
pulse returns plug the injectors electrical connectors in one at a time until the
pulse fails and then replace that injector).
If this test revealed that there was no pulse but system has power, the PCM is
not generating a fuel injector trigger. If there is no trigger to the fuel injector
it will not allow fuel to enter into the engine. Some of the most common reasons
that can cause this condition include a shorted fuel injector, injector wiring damage
or shorted PCM. While
the injector trigger wire is off, test the fuel injector windings by setting the
multimeter (voltmeter) to ohms and attach the leads to either side of the injector.
Your reading should be between 11 and 18 ohms. Test all of your injectors; if one
injector reading is considerably different from the others replace that injector.
Check the fuel pressure regulator, remove the vacuum line feeding the fuel pressure
regulator, check for the presence of fuel, if fuel is present the diaphragm inside
the regulator has ruptured and is feeding raw fuel into the engine causing it to
run rough.
Fuel Injector
Check Air Intake Boot - An air intake boot is designed to transfer
air from the mass air flow meter to the throttle bore. The PCM monitors this air
flow and corrects fuel input. When an air intake boot fails it causes the PCM to
respond by inputting more fuel than is necessary. This condition causes black smoke
from the exhaust system. To check for this problem remove air intake boot to inspect
for cracks or tears and replace if needed.
Torn Air Intake Boot
Check Engine Light - Service Engine Soon
If the check engine light is illuminated the PCM has detected a malfunction that
could be causing the problem,
scan the PCM to retrieve trouble codes and repair as needed.
Preventive Maintenance
To check your car's mixture you will need to use a gas analyzer to test your
exhaust gases. This will measure the carbon monoxide, hydrocarbon, nitrogen oxide
and oxygen content of your exhaust. During a normal smog inspection the fuel/air
mixture is tested and a report generated. When a tune up is performed the spark
plug end insulator can tell you whether you have a lean or rich mixture. Brownish
grey is the desired color and confirms proper mixture. Black and sooty means the
mixture is too rich while white to light grey confirms a lean mixture. Fuel injection
systems rely on pressurized fuel to operate. 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.
Maintenance
Maintenance for a vehicle is something that is often overlooked. From blank stares
when asked when the last oil change occurred, to the even stranger looks that occur
when asking when the last tire rotation was completed. It is very important to
maintain oil changes
and tune-ups that are performed on schedule. Proper maintenance to your car is a
good way to keep all internal engine parts from becoming damaged prematurely. Without
oil lubrication an engine will quickly become severely damaged. Anytime you are
able to lengthen the life of the engine and help avoid breakdowns it is beneficial
to the motoring experience.
Sometimes it is advisable to seek a professional ASE or other certified mechanic
to trouble shoot the problem for the blue smoke condition. Never avoid engine problems
as they can cause a simple and inexpensive repair to escalate to a costly repair
that could have been avoided. Choosing the right mechanic or repair shop for your
needs is often the biggest issue, however many times it can take just a referral
from a friend or relative in order to find an appropriate repair shop. Poorly maintained
engines are much more prone to problems such as smoking. The excessive friction
leads to catastrophic engine failure. Preventative maintenance is cheap insurance
to ensure that your vehicle runs as smooth as possible for many miles to come.
If further technical assistance is needed, our certified car repair technicians
are ready to answer your car questions.
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