Free Car Repair Advice by Professional Mechanics
Troubleshooting
/ Excessive Smoke
Introduction:
A small amount of smoke from the exhaust pipe of the car is normal.
Excessive smoke is created by a malfunction. The smoke is cause by excessive
fuel or engine oil. If this condition is allowed to continue it can affect the
exhaust system. Failures can range from catalytic converter becoming plugged to
engine overheating and poor fuel economy. Below we have listed the most common
causes for this condition.
Troubleshooting Procedure
A. 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
B. 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.
C. 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 ECM 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 ECM/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
D. Check Air Intake Boot. An
air intake boot is designed to transfer air from the
mass air flow meter to the throttle bore. The
ECM monitors this air flow and corrects fuel input. When an air intake boot
fails it causes the
ECM 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.
For exact specific repair procedures for any of the steps above visit our
online repair
manual page.
Troubleshooting
/
Excessive Smoke
Additional "How to" Car Repair or Services
1. How to Replace
Air Filters?
2. How to Change
a Cabin Filter?
3. How to Change
Oil and Filter?
4. How to Tune Up with
Throttle Bore Service?
5. How to Replace
a Radiator?
6. How to
Replace Fuel Filters?
7. How to Read Trouble Codes?
8. How Filters Work?
9. How to Replace
Front Brake Pads?
10. How to Replace Rear
Brake Pads?
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