Today's engines have been designed to have more output power and lower emissions
than ever before. So when the output of your vehicles engine is compromised it is
easily detected. When your vehicle has low power output it can mean several different
things are occurring. You should know while your car has low performance it could
be damaging components while you drive. Example: The emergency brake is on and you
did not notice, this condition will burn up the rear brake pads or shoes and cause
premature emergency brake failure. Or, the fuel filter is clogged causing the
fuel pump to labor which can cause premature fuel pump failure. There are basically
two kinds of low power conditions either the engine is running rough causing low
power or the engine is running smoothly but still has low power. If the engine is
running smoothly but has low power you are in the right place. If your engine is
running rough causing low power please visit.
Why does my engine run rough?
Car Repair Guide - READ COMPLETELY BEFORE BEGINNING
Step 1 -
Scan for Trouble Codes - Check to see if the "service engine soon" light
is on, if not continue to the next step. If the "check engine" (same thing as
a service engine soon light, different manufacturers call it different things)
light is illuminated you need to have the computer
scanned
for trouble codes. Use a simple
scanner tool to retrieve
trouble codes and check if they relate to the specific problem, like a
fuel pump circuit failure code. If a
trouble code is present but does not pertain to the immediate problem like
an EVAP code ignore it until a later time, after the engine is running properly.
The reason we repair non-related codes after the engine is running properly
is because sometime false codes can be triggered by a poorly running engine.
Once the engine is running properly the code present might cycle and turn itself
off. You might say "if the engine isn't running right shouldn't it have a check
engine light and a trouble code?" Sometimes conditions occur that will not
be detected by the computer, example: if the intake or exhaust valve operation
fails the computer cannot detect the failure because the problem is not sensor
related, so the engine has no power and the computer thinks everything is ok
with no codes. If the trouble code retrieved relates to a low power like a
Mass Air Flow (MAF) sensor or ignition coil system failure repair these
problems and re-test system. If no trouble codes are present proceed to the
next step.
Step 2 -
Check the Air Filter - A plugged air filter not allowing the proper amount
of air into the engine. If air is not allowed to enter the engine's intake it
will limit the engine power output. To check your engine air filter open the
hood and remove the
air filter from its housing and inspect, replace as needed and recheck.
Step 3 -
Check the Fuel Filter - Several conditions can cause low power, one of the
most common reasons is a clogged fuel filter not allowing the proper amount
of fuel pressure and volume into the fuel injection system. To check for
this condition remove the fuel filter and drain excess fuel from the filter,
next wipe any excess fuel from the filter. By blowing through the filter you
can determine if the filter is clogged, you should be able to blow through it
very easily. If you cannot blow through it or it is difficult replace the
fuel
filter with a new unit and recheck system. Some fuel filters utilize a special
release tool available at our tool store:
Fuel filter release tool, if the fuel filter is ok proceed to the next step.
Step 4 -
Check Fuel Pump Pressure and Pressure Regulator - Fuel pump is worn
providing low fuel pressure to the fuel injection system. A fuel pump that
is faltering providing low system fuel pressure/volume will cause low power. Your car's
engine depends on constant fuel under pressure to supply the
fuel injection system properly. Your car's
fuel pump performs this action and is located in or near the gas tank. The
injection system meters fuel through the injectors and into the engine. Many
engine run drivability problems can be related to a weak or failing fuel pump. Problems
can range from hard starting in the morning, low power and stalling while driving.
Most vehicles have a fuel pressure test port somewhere on the fuel rail, use
a flashlight to locate it on your engine or consult a
repair manual. Also test the fuel pressure regulator performance; if the
regulator is stuck or leaking the engine will not receive the additional fuel needed for
power. If the fuel system pressure is ok proceed to the next step.
Fuel Injection Pressure and Pressure Regulator Test
Step 5 - This step is for adjustable distributor type
ignition systems only. If your car has a DIS (distributor-less ignition
system) skip this step. Ignition timing is very important in achieving maximum
power from your engine. If the timing is adjusted too far advanced or retarded
(in front or behind the timing mark) in relationship
to the engine crankshaft it will have low power output. To check your engines
timing adjustment a timing light is needed. Once the timing light is hooked
up to the
battery locate the under hood emissions sticker that has the engine timing
specification and instructions. If you can't find the under hood sticker or it
is illegible consult a car
repair manual. If the engine timing is ok proceed to the next step. If the
engine timing is way off (20 degrees or more) check the
timing belt or
timing chain, the crankshaft camshaft correlation might be off.
Engine Configuration with Camshaft Operation
Step 6 - Checking the MAF, (mass
air flow) and MAP (manifold absolute pressure) sensors. The MAF or MAP help
the ECM/PCM determine how much air the engine is consuming and distributes the
proper amount of fuel. If these sensors become weak they can misread and cause
the ECM/PCM to think the engine is turning slower than it is, in turn giving
the engine less fuel and producing less power. You might say wouldn't the computer
see a problem and illuminate the service engine soon light?- MIL (malfunction
inductor lamp) and the answer is not always. The
computer ECM/PCM is designed to detect a shorted sensor or a sensor that
is way out range. If the sensor is a little off but it is still within range the
service engine soon MIL will not illuminate. This test procedure is simple but
unique to each car, for this you will need a
repair manual.
Step 7 - Check for severely worn or misadjusted spark
plugs. Engine timing is crucial to power output, if the spark plugs are
severely worn or have a misadjusted air gap the timing of the spark can be
delayed or ineffective causing power loss.
To
check your engine's spark plugs wait until the engine is cold, then remove
any spark plug and inspect. You are looking for the correct air gap between the
electrodes, if the gap is incorrect remove all
spark plugs and recheck. If the spark plugs are ok proceed to next step.
Step 8 - Check the
timing belt or
timing chain setting, the crankshaft and camshaft must stay in proper correlation.
The procedure for checking crankshaft to camshaft correlation varies on each
car. You will need to gain access to the timing belt
or chain marks. Once you have gained access check your timing marks here,
timing belt or
timing chain setting. Correct as needed and recheck engine, if the timing
correlation is correct proceed to next step.
Step 9 - Check the exhaust system for blockage. A
plugged catalytic converter can cause low engine power by not allowing the
engine exhaust to exit the engine properly. To check for this condition take
your car for a 15 minute drive allowing the exhaust system to warm, park the
car safely and use a
pocket IR thermometerlaser temperature reader to measure
the temperature of the exhaust pipe entering the catalytic converter and the
exhaust pipe leaving. The temperature should be lower going into the
catalytic converter and hotter leaving the catalytic converter, if not there
may be a restriction inside the converter.
Plugged Catalytic Converter from Broken Catalyst Material
Example: the temperature entering
the catalytic converter is 300 degrees and exiting the catalytic converter is
450 degrees. This means the catalytic converter is working properly, if the
temperature is the same or lower the catalytic converter is not working and
is probably plugged.
Step 10 - Check the
engine compression, as the engine depends on compression to ignite the fuel
air mixture. If an engine has major wear is will not produce the proper amount
of power. A
compression test can be performed to check for wear or internal damage. A compression
gauge is needed to test the engine cylinders. There are two types of gauge
styles, one threads into the spark plug hole which is more accurate. The other
style of gauge is designed with a rubber plug that is meant to be pressed
against the spark plug hole, this style of gauge is difficult to use.
Perform an engine cylinder compression test.
Step 11 - Sometimes the engine will have good power but
it is not getting to the drive wheels. If you are driving and the engine sounds
like it is working hard but the car is not going anywhere it could be the transmission
clutch or clutches are slipping. When a clutch or clutches in a manual
(standard) or automatic transmission wear they can slip not allowing the
power from the engine to be transferred to the drive wheels. In this case
the only fix is to replace the clutch or clutches depending on automatic or
standard transmission. If this is not the condition continue to next step.
Step 12 - Some cars have an ignition trigger system that
bases the engine timing off of the crankshaft harmonic balancer. If this
balancer comes loose it can cause the keyway in the crankshaft to dig its
way into the balancer causing the timing to retard causing low power. To
check for this condition remove the harmonic balancer and inspect, replace
if needed and reassemble.
For exact specific repair procedures for any of the steps above visit our
online repair
manual page.
WARNING! Always have the vehicle under inspection on level
ground, in park with the emergency brake on. Always wear protective eyewear, gloves
and necessary clothing before inspection or work begins. Never crank an engine over
when anyone is near the battery or engine. Always have an operational fire extinguisher
close by, obey all first aid instructions in the event of an injury. Never stand
in front or behind a vehicle when starting or running. When engine is cranked over
keep hands and clothing away from rotating components. Anyone with a heart pacemaker
should not perform these tests.
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