Hesitation Definition - An engine hesitation is an interruption of continuous
power during acceleration. When
a engine is hesitating it will cause the car to lunge or surge during acceleration
which will cause a sudden jerk as the car slows down. This condition can cause dangerous
situations in heavy traffic when drivers behind you expect you to move continuously
forward. An engine hesitation can be difficult to detect because as the
engine is running under power
you have to decide if the engine is shutting off for a split second or if the
engine is just losing power temporarily.
If your engine stalls and then restarts please visit,
why does my engine cut out. Please note that
while an engine is hesitating it could cause damage to other components. Example:
When an engine hesitates is will lose power then re-gain power quickly, this adds
stress to the vehicles derive train and could cause premature failure. There are
several systems are involved that can cause engine hesitation. We have listed some
common reasons for engine hesitation
Car Repair Guide
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 manufactures call
it different things) light is illuminated you need to 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.
How to Scan for Trouble Codes Video
Check the Air Filter - A
plugged air filter will
not allow the proper amount of air into the engine. If air is not allowed to enter
the engine's intake it will can cause the engine to hesitate. To check your engine
air filter open the hood and remove
the air filter from its housing and inspect, replace as needed and recheck.
How to Replace an Engine Air Filter Video
Check the Fuel Filter - Several conditions can cause engine
hesitation, 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 out tool store, if the fuel filter checks out
ok proceed to the next step.
Check for Broken or Dilapidated Vacuum Hoses - Inspection of
the vacuum hoses or air intake boot on and around the engine is simple. Your car's
engine is designed to run on a system that can hold vacuum. Vacuum hose are typically
connected to the engine intake manifold and will supply engine vacuum to various
accessories like power brakes. Some cars are designed with a larger vacuum transfer
hose that connects the intake manifold to the
IAC (idle air control) motor.
If broken or dilapidated these vacuum lines can cause the engine to lose vacuum
which will allow the engine to
run rough and stall.
Inspect all engine and accessory vacuum lines look for missing, torn or dilapidated
lines and replace as needed. Also have a helper rest their foot on the gas pedal
just enough to keep the engine running and double check the engine when it is running
to listen for any whistling noise coming from the engine that is not usually present.
Follow the noise and inspect vacuum lines in that area, also when the engine is
running it will pull inward a broken or weak piece of the hose to create a larger
vacuum leak. Check the integrity of all vacuum hoses at each end of the hose, typically
this is where a vacuum hose fails. If all vacuum hoses check "okay" proceed to the
next step.
Failed Air Intake Boot
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 hesitation. 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 car 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 okay proceed to the next step.
Testing Fuel Pressure Video
Adjust the Distributor Ignition Systems - If your car engine
has a DIS (distributor-less ignition system) skip this step.
Ignition timing is very important
in achieving maximum power from your engine with a hesitation. If the timing is
adjusted too far retarded (behind the timing mark) in relationship to the engine
crankshaft it will cause an engine to hesitate. 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 includes 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 okay 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.
Checking the MAF, (mass air flow) and MAP (manifold absolute pressure)
Sensors - The
MAF or MAP help the
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 PCM
to think the engine is turning slower than it is, in turn giving the engine less
fuel and producing a hesitation. 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 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
car repair manual.
Check for Severely Worn or Mis-adjusted Spark Plug Gap - The
engine timing is crucial to engine power
output, if the spark plugs
are severely worn or have a mis-adjusted air gap the timing of the spark can be
delayed or ineffective. 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 okay proceed to next step.
Check the Timing Belt or Timing Chain Setting - The crankshaft
and camshaft must stay in proper correlation. If this correlation is off the engine
will hesitate. The procedure for checking crankshaft to camshaft
timing 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.
Transmission Clutch Problems - 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 and be lost due to lack of friction. 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.
Harmonic Balancer to Crankshaft Timing - Some cars have an
ignition trigger system that
bases the engine timing off of the crankshaft
harmonic balancer. If this
balancer comes loose is can cause the keyway in the crankshaft to dig its way into
the balancer causing the timing to retard which will cause engine hesitation. To
check for this condition remove the harmonic balancer and inspect, replace if needed
and reassemble.
If further assistance is needed, our certified car repair technicians are ready
to answer your car questions.
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