"I feel like the engine revs are heavier than before."
"The tachometer doesn't climb smoothly even when I press the accelerator pedal."
"The engine doesn't rev as high as it used to."
When driving a car, you may notice such changes.
This symptom is commonly referred to as:
"Poor engine response" or "Engine not revving up well."
However, there isn't just one cause for an engine feeling sluggish.
Ignition system
Intake system
Fuel and combustion
Engine oil
Sensors and electronic control
Exhaust system
Internal engine friction
Transmission and drivetrain
Various factors like these can be involved.
Additionally,
"Poor engine response"
and
"Poor car acceleration"
are similar but slightly different.
This time, we will explain the mechanism behind an engine feeling heavy and the common causes you should check.
What exactly is "engine response" (fukeagari)?
"Fukeagari" (engine response/revving up) is not an official performance metric but a term generally used to describe how an engine's RPM increases.
When you press the accelerator pedal:
The engine RPM rises quickly.
There's no feeling of hesitation or catching.
The RPM increase is smooth.
The change in RPM when releasing the accelerator is also natural.
Such a state may be described as:
"Good engine response."
Conversely,
The RPM doesn't rise easily even when you press the accelerator.
You feel a hesitation (misfire) during acceleration.
The engine feels rough.
It feels heavier than before.
It struggles to reach high RPMs.
This state may be described as:
"Poor engine response."
"Engine response" and "acceleration" are not the same.
This is an important point.
Engine response refers to:
How the engine RPM changes.
On the other hand, car acceleration refers to:
How the vehicle speed increases.
For example, in CVT-equipped vehicles, when the accelerator is pressed, the engine RPM may rise first, with the vehicle speed following afterward.
In this case,
The engine revs well.
However, the way the vehicle speed increases gives a different impression.
Conversely, engines with large low-end torque may accelerate powerfully without needing to rev very high.
Therefore,
Engine response.
Throttle response.
Actual acceleration performance.
must be considered separately.
Why does the engine RPM increase?
Simplifying a gasoline engine, accelerator operation changes the intake air volume, etc., and fuel injection and ignition are controlled accordingly.
The force generated by combustion pushes the piston,
rotating the connecting rod.
and the crankshaft.
When the accelerator is pressed, if the engine produces more torque than is required to maintain its current rotational state, the RPM will increase.
However, there is resistance within the engine from:
Pistons and cylinders.
Piston rings.
Crankshaft.
Camshaft.
Valve train.
Oil pump.
Ancillary components.
In short,
the force generated by combustion
and
the resistance that hinders rotation
The rate at which the engine revs up changes depending on the balance between these two.
Cause 1: Condition of spark plugs and ignition system
For gasoline engines, one of the first things to consider is the ignition system.
Gasoline engines ignite a compressed air-fuel mixture with a spark from the spark plug to cause combustion.
Spark plug electrodes wear out with use.
If the electrodes are in poor condition or the gap is not appropriate, it can become difficult for the spark plug to fire properly under certain conditions.
As a result,
Misfires.
Hesitation (stuttering).
Vibrations.
Reduced starting performance.
Lack of power during acceleration.
may occur.
Especially under high-load conditions, such as when the accelerator is fully pressed, the conditions required for ignition become more stringent.
If you experience "no problem when driving slowly, but the engine doesn't rev smoothly when accelerating hard," then the ignition system, including spark plugs and ignition coils, should be checked.
Cause 2: Condition of the intake system
For an engine to combust properly, it needs to take in the necessary amount of air.
Air generally enters the engine through:
Air filter.
Intake duct.
Throttle.
Intake manifold.
If the intake system's condition prevents sufficient air intake, it can affect engine performance.
For example,
Significant clogging of the air filter.
Abnormalities in the intake path.
Dirt around the throttle.
Sensor malfunction.
However,
It's not as simple as concluding that "poor engine response is due to a slightly dirty air filter."
Modern cars are electronically controlled, so a comprehensive check, including diagnostic fault codes, is necessary.
Cause 3: Throttle and electronic control
Many modern cars use electronic throttles.
Instead of a direct wire connection between the accelerator pedal and the throttle valve, the throttle opening is controlled using information such as:
Accelerator operation.
Engine RPM.
Vehicle speed.
Load.
Transmission.
Various sensors.
Therefore,
It's not a simple 1:1 relationship where pressing the accelerator pedal 50% means the throttle will open exactly 50%.
The ECU controls it considering factors like:
Engine protection.
Fuel economy.
Exhaust emissions.
Traction control.
Shift control.
Consequently, depending on the car model, even in a normal state,
You may feel that "the RPM rises a little slowly in response to accelerator input."
If it has been like this since you got the car, it might be a characteristic of the vehicle.
On the other hand,
If it used to rev easily but suddenly changed,
you need to investigate other causes.
Cause 4: Fuel injection and combustion status
For an engine to run smoothly,
Air.
Fuel.
Ignition.
must be combined in appropriate conditions.
If there are problems with the fuel injection system or combustion status,
Unstable idling.
Hesitation (stuttering) during acceleration.
Non-smooth RPM increase.
Increased vibrations.
Such symptoms may appear.
Related parts include:
Injectors.
Fuel pump.
Fuel pressure system.
Air flow meter.
O2 sensor.
A/F sensor.
However, it is difficult to identify the cause based solely on driving feel.
In modern cars, checking error codes and sensor data with a diagnostic tool is crucial.
Cause 5: Engine oil condition and viscosity
Inside the engine, numerous parts move at high speeds.
Engine oil properly manages the friction between these parts.
Engine oil has multiple roles, including:
Lubrication.
Cooling.
Cleaning.
Sealing.
Rust prevention.
The viscosity of the oil also affects the engine's rotational feel.
Higher viscosity isn't always better, nor is lower viscosity.
Manufacturers specify the viscosity based on the engine design.
For example, for an engine specified to use 0W-20 oil, it's not appropriate to choose a significantly different viscosity simply because you think "higher viscosity seems to protect the engine more."
Conversely, choosing an extremely low viscosity that isn't specified is also not recommended.
The basic rule is to:
Check the specifications and viscosity listed in the owner's manual.
Why does oil viscosity change the rotational feel?
Engine oil forms an oil film between moving parts.
At the same time, the liquid itself also has viscous resistance.
Generally, as viscosity increases, the resistance required to move the fluid also tends to increase.
Therefore, under certain conditions, it can affect the impression of engine rotation.
However, this does not mean that:
"Simply using low-viscosity oil will make the engine rev lighter."
Ensuring the necessary oil film and lubrication performance is a prerequisite.
It is important to use the manufacturer-specified viscosity appropriate for your car model, engine, and operating environment.
Cause 6: Cold engine
The engine's condition differs immediately after starting and after warming up.
When cold,
Engine oil viscosity.
Fuel injection control.
Idling control.
Temperature of each component.
These are all different from when the engine is warm.
Therefore, even if the engine's rotational feel seems a bit heavy immediately after starting, it doesn't necessarily indicate an abnormality.
This difference is particularly noticeable in cold environments, such as during winter.
It's important to compare the feel when the engine is sufficiently warmed up.
However, if the abnormality persists even after warm-up, an inspection is necessary.
Cause 7: Exhaust system resistance
An engine not only takes in air but also needs to expel exhaust gases after combustion.
The exhaust system includes:
Exhaust manifold.
Catalytic converter.
Muffler.
If there's an issue with the exhaust system that prevents exhaust gases from flowing smoothly, it can affect engine performance.
For example, if exhaust resistance drastically increases due to an abnormality inside the catalytic converter,
It struggles to reach high RPMs.
It lacks power under load.
The RPM doesn't increase beyond a certain point.
Such symptoms may occur.
However, the exhaust system becomes very hot, so it is dangerous for general users to easily disassemble or inspect it.
If an abnormality is suspected, it is safer to have it inspected at a repair shop.
Cause 8: Internal engine friction and mechanical condition
There is various friction inside the engine.
For example,
Piston rings and cylinders.
Crankshaft bearings.
Camshaft.
Valve train.
Chain and belt systems.
Oil pump.
Friction itself is not an anomaly.
In fact, some contact and oil films are necessary for the engine to operate normally.
What's important is whether:
it is in the designed and appropriate condition.
If there is:
Insufficient lubrication.
Abnormal wear of parts.
Bearing malfunctions.
Oil management problems.
Then rotational resistance may increase.
However, these internal conditions cannot be diagnosed solely by the "feel of engine response."
If accompanied by unusual noises or oil pressure warnings, it is important to stop driving and seek inspection.
Resistance from ancillary components can also have an impact.
The engine doesn't just turn the crankshaft.
Depending on the car model, it also drives:
Alternator.
Air conditioning compressor.
Water pump.
Various pumps.
When the air conditioning is used, you may feel that:
The engine load increased slightly.
The idling sound changed.
This is related to the load from these ancillary components.
Normally, the ECU compensates, but if there is abnormal resistance in the ancillary components, it can affect the engine's feel.
For turbo vehicles, supercharging also plays a role.
In turbo engines, the supercharging state also affects the impression during acceleration.
Turbochargers use the energy of exhaust gases to compress intake air.
Therefore, if there are problems with the:
Intake system.
Exhaust system.
Boost pressure control.
Intercooler.
Piping.
Then the engine may not produce its full torque.
In this case,
Instead of the engine itself not revving up,
you may feel a lack of power under load, which consequently prevents the engine from revving out.
You might feel "poor engine response" due to AT or CVT influence.
Even if there's no actual engine problem, the transmission control might make the engine's revving feel different.
In ATs,
Upshifts.
Kick-downs.
Lock-ups.
These cause engine RPM to change.
CVTs continuously vary the gear ratio to try and keep the engine in an efficient RPM range.
Therefore,
The way it revs up might feel different compared to a manual transmission car you used to drive.
The impression might differ between Sport mode and Normal mode.
It's important not to judge an engine malfunction solely by the "feel of engine response."
Can I determine it by revving in neutral?
To check the engine's responsiveness,
You might think, "I can tell by revving it in P or N."
However, this alone cannot provide an accurate judgment.
The load on the engine in an unloaded state is significantly different from when driving.
Furthermore, some modern cars have control systems that limit engine RPM in P or N ranges.
Therefore,
You cannot determine a malfunction simply because it doesn't rev to high RPMs in P or N.
It is important to avoid excessive revving and follow the manufacturer's owner's manual and maintenance standards.
Caution if the engine "doesn't rev to high RPMs"
Rather than just feeling a little heavy, if:
It absolutely won't go above a certain RPM.
The engine warning light is on.
There's severe vibration.
There's obvious misfiring.
There's an unusual noise.
Black or white smoke suddenly increased.
There's a burning smell.
The water temperature warning is on.
The oil pressure warning light is on.
In such cases, it's best not to consider it a normal "poor engine response" issue.
There's a possibility that a fail-safe control is active to protect the engine, limiting its output.
Do not continue driving; consult a dealership or repair shop.
First things to check when the engine response is poor
If you notice an abnormality, first categorize how it differs from before.
When did it change?
Is it only when cold?
Does it persist after warm-up?
Is it only at low RPMs?
Does it not rev out at high RPMs?
Does it change with the A/C on or off?
Is a warning light illuminated?
Are there vibrations or unusual noises?
Have you recently had an oil change?
Have any parts been replaced recently?
Having this information will make it easier for a repair shop to identify the cause.
Check basic maintenance
If there are no clear symptoms of malfunction, it's important to start by checking the basic maintenance status.
For example,
Engine oil change interval.
Oil level.
Specified viscosity.
Air filter.
Spark plugs.
Other regularly replaced parts.
Spark plugs, in particular, are consumables.
Over long periods of use, electrodes can wear out and the spark gap can widen, which may lead to misfires.
Replacement intervals vary depending on the car model and plug type, so check your owner's manual or service records.
Will additives improve engine response?
This needs to be considered carefully.
Engine oil additives and fuel additives each have different purposes.
However,
Poor engine response does not automatically mean it will be fixed by adding an additive.
For example,
A faulty spark plug.
A problem with the ignition coil.
A sensor malfunction.
A problem with the catalytic converter.
An internal engine failure.
These conditions cannot be repaired with additives.
The first thing needed is to distinguish between:
Is it a malfunction?
Is it a maintenance issue?
Is it a characteristic inherent to the vehicle?
Do not change oil viscosity just to "lighten engine response."
It is also not recommended to:
Switch to an oil with significantly lower viscosity than specified.
The oil viscosity is not determined solely by rotational resistance.
Oil film retention.
High-temperature protection.
Engine design.
Operating environment.
These factors are considered when specifying the viscosity.
The basic rule is to use the manufacturer-specified viscosity and grade.
Regarding oil viscosity,
The article "What's the difference between 0W-20 and 5W-30?" explains it in detail.
Engine Response and Friction Loss
An engine cannot convert all of the fuel's energy into driving force for the tires.
Inside the engine,
Friction.
Pumping losses.
Ancillary drive.
A portion of the energy is lost due to these factors.
One such loss is friction loss.
If frictional resistance increases, the proportion of the force generated by combustion that is used to turn the engine itself also increases.
Therefore, friction and lubrication are important topics when considering the engine's rotational feel.
However,
You cannot conclude that "poor engine response = increased friction."
It is necessary to consider ignition, intake, combustion, control, and other factors comprehensively.
Is it a malfunction if the engine feels heavier than when it was new?
Not necessarily a malfunction.
As a car is used,
Tires.
Oil.
Ignition system.
Intake system.
Drivetrain.
The condition of these components changes.
Also, as drivers become accustomed to their cars, they may become more sensitive to changes than before.
What's important is:
Did it change suddenly and significantly?
Did it change gradually?
Is it accompanied by other symptoms?
If it changed suddenly or is accompanied by a warning light, prioritize inspection.
Next Science's view on "Rotational Feel"
Engine performance cannot be fully explained by just:
Maximum power output.
Maximum torque.
When actually driving, there's a certain feeling, such as:
Smoothness of rotation.
Response when pressing the accelerator.
Vibration.
Sound.
Naturalness of RPM increase.
And in the background, there are multiple factors:
Combustion/Fuel.
Friction/Lubrication.
Electronic environment.
Mechanical condition.
At Next Science, we don't just focus on simply adding something to increase maximum output, but rather consider "driving quality" from the perspective of:
Where energy is generated.
Where it encounters resistance.
How it is transmitted.
Engine response is one element that helps us feel the vehicle's condition in this way.
Summary: Poor engine response has multiple causes.
Engine response generally refers to the sensation of how quickly the engine RPM increases in response to accelerator input.
Possible causes for poor engine response include:
Spark plugs and ignition system.
Intake system.
Electronic throttle and control.
Fuel and combustion status.
Engine oil.
Cold engine conditions.
Exhaust system.
Internal engine friction.
Ancillary components.
Turbo/supercharging system.
Transmission control.
It is important not to jump to conclusions about a single cause.
First, check:
Is it only when cold?
Does it persist after warm-up?
Is it at low or high RPMs?
Are there warning lights or vibrations?
Has basic maintenance been performed?
And if accompanied by:
Warning lights.
Severe vibrations.
Unusual noises.
Smoke.
Unusual odors.
Obvious misfires.
Sudden loss of performance.
Do not try to remedy it with additives or self-diagnose; instead, have it inspected by a dealership or repair shop.
To maintain a light and smooth-running engine, it is more important to properly maintain the vehicle's basic condition than to rely on special methods.