"I feel like the acceleration isn't as responsive as it used to be."
"When I press the accelerator, the car feels heavy."
"It doesn't seem to be a breakdown, but for some reason, the ride isn't smooth."
When you've been driving the same car for a long time, you might notice these kinds of changes.
However, a car's acceleration isn't solely determined by "engine horsepower."
Drivers perceive the car as "light," "heavy," "responsive," or "slow to accelerate" as a result of various factors interacting, such as the engine's combustion state, intake, ignition, transmission, tires, and friction resistance in each part.
This time, we will explain the main causes of poor car acceleration in an easy-to-understand manner, from the perspectives of the engine, drivetrain, and friction.
What does "poor acceleration" mean for a car?
There are several ways to perceive "poor acceleration."
For example:
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The speed doesn't increase quickly even when pressing the accelerator
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Sluggishness when starting
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Less power on hills than before
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Engine RPM increases but vehicle speed doesn't follow
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Slow response to accelerator input
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The entire car feels heavier than before
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Doesn't coast smoothly when releasing the accelerator
These are the symptoms.
Even with similar "heaviness," the causes differ.
Therefore, when considering acceleration, it's important to focus on "where power is being lost."
Cause 1: Deterioration of spark plugs and ignition system
In a gasoline engine, spark plugs ignite the air-fuel mixture, causing it to combust.
If spark plugs deteriorate, it can become difficult for sparks to fly, leading to unstable combustion.
Toyota also cites spark plug degradation as one of the main potential causes when "acceleration has become sluggish." NGK also explains that if the electrodes wear out, misfires can occur, preventing the engine from delivering its full performance.
If the ignition state deteriorates, it can lead to symptoms such as:
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Sluggish acceleration
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Engine vibration
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Unstable idling
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Worsening fuel economy
This is one of the basic items to check first if you feel that "the car isn't as powerful as it used to be when I press the accelerator."
Cause 2: Dirty air cleaner or insufficient air intake
For an engine to generate power, it needs not only fuel but also sufficient air.
The air cleaner cleans this air and sends it to the engine.
If the air cleaner becomes dirty and clogged, it becomes difficult for the engine to draw in enough air.
Honda also explains that if a dirty or clogged air cleaner element is left unaddressed, engine performance will decrease, leading to poorer fuel economy.
To use a human analogy, it's like trying to run without being able to breathe properly.
In particular, if you experience:
"Doesn't rev smoothly at high RPMs"
"Feels underpowered on hills"
"I have to press the accelerator deeper than before"
In such cases, the intake system is also a point to check.
Cause 3: Combustion state deviates from normal
An engine doesn't just burn gasoline.
It operates while finely controlling the amount of air and fuel, ignition timing, fuel injection, and combustion temperature.
If there is a malfunction in the fuel injection system, sensors, or ignition system, the combustion state can be disrupted, potentially affecting acceleration performance.
In other words,
Even with "the same engine"
and "the same horsepower,"
it doesn't always generate power in the same state.
When considering a car's condition, it's important not only to look at the simple maximum output but also "how stably it combusts and converts that into power."
Cause 4: Condition of the AT/CVT and other drivetrain components
The power generated by the engine doesn't directly reach the tires.
It is transmitted to the tires through many parts, such as the transmission and driveshaft.
Therefore, even if there is no problem with the engine itself, the feeling of acceleration can change depending on the condition of the drivetrain.
SUBARU suggests checking ATF/CVT fluid if you experience symptoms such as:
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Increased shock during gear changes
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Sluggishness during starting or acceleration
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Worse fuel economy than before
For example:
You press the accelerator.
The engine RPM increases.
However, the vehicle speed doesn't increase as much as expected.
In such cases, you need to consider not only the engine but also the path that transmits power to the wheels.
Cause 5: Tire pressure and rolling resistance
When a car moves forward, resistance is also generated by the tires.
This is called "rolling resistance."
Tires are constantly deforming while driving, and some of that energy is lost as heat due to this deformation.
According to Bridgestone, tire rolling resistance is related to tire deformation, ground friction, and air resistance, with tire deformation having the largest impact.
Furthermore, if tire pressure decreases, the amount of tire deformation increases, and rolling resistance tends to increase as well.
This can lead to feelings of:
"Doesn't coast when I release the accelerator"