"The engine feels heavier than before."
"When I press the accelerator, the RPM doesn't increase smoothly."
"The engine doesn't rev as well at high RPMs."
You may experience these changes while driving your car.
Generally, these symptoms are described as
"poor engine revving."
However, there isn't just one cause for poor revving.
Ignition system.
Intake system.
Fuel and combustion.
Engine oil.
Sensors and electronic control.
Exhaust system.
Internal engine friction.
Transmission and drivetrain.
Various factors are involved.
Also,
"poor engine revving"
and
"poor car acceleration"
are similar but slightly different.
This time, we will explain how the engine feels heavy and the common causes you should check.
What is "revving up" in the first place?
"Revving up" is not a formal performance indicator, but a general term describing how engine RPM increases.
When you press the accelerator, if the engine RPM:
Rises quickly.
Doesn't feel like it's getting stuck midway.
Rises smoothly.
Changes naturally when you release the accelerator.
Such a state is often described as
"good revving."
Conversely, you might experience
"poor revving"
if:
The RPM doesn't rise easily even when you press the accelerator.
You feel it hesitating midway.
The rotation feels rough.
It feels heavier than before.
It doesn't rev up to high RPMs easily.
"Revving" and "Acceleration" are not the same
This is an important point.
Engine revving refers to
how the engine speed changes.
On the other hand, car acceleration refers to
how the vehicle speed increases.
For example, in a CVT car, when you press the accelerator, the engine speed may increase first, and then the vehicle speed follows.
In this case,
the engine revs well,
but the vehicle speed increase gives a different impression.
Conversely, an engine with high low-speed torque may accelerate powerfully without needing a large increase in RPM.
Therefore, it's necessary to distinguish between
revving,
throttle response,
and actual acceleration performance.
Why does the engine speed increase?
To simplify gasoline engines, when you operate the accelerator, the intake air volume changes, and fuel injection and ignition are controlled accordingly.
The force generated by combustion pushes the piston,
rotating the connecting rod
and crankshaft.
When you press the accelerator, if the engine generates torque exceeding the force required to maintain its current rotational state, the engine speed will increase.
However, inside the engine, there is resistance from:
Pistons and cylinders.
Piston rings.
Crankshaft.
Camshaft.
Valve system.
Oil pump.
Auxiliary components.
In other words, the rate at which the engine revs up depends on the balance between
the force generated by combustion
and
the resistance hindering rotation.
Cause 1: Condition of spark plugs and ignition system
One of the first things to consider in a gasoline engine is the ignition system.
A gasoline engine ignites a compressed air-fuel mixture with a spark from the spark plug.
Spark plug electrodes wear down with use.
If the electrodes are in poor condition or the gap is incorrect, it can be difficult to generate a normal spark under certain conditions.
As a result, symptoms such as:
Misfires.
Hesitation.
Vibration.
Difficulty starting.
Lack of power during acceleration.
may occur.
Especially under high load conditions when the accelerator is pressed, the conditions required for ignition become more stringent.
If you experience "no problem when driving slowly, but the RPM doesn't rise smoothly when accelerating hard," then the spark plugs and ignition coils should be checked as part of the ignition system.
Cause 2: Condition of the intake system
For proper engine combustion, the necessary amount of air must be drawn in.
Air typically enters the engine through the:
Air cleaner.
Intake duct.
Throttle.
Intake manifold.
If the intake system's condition prevents sufficient air intake, it can affect engine performance.
For example, this could be due to:
Significant air cleaner blockage.
Abnormality in the intake path.
Dirt around the throttle.
Sensor malfunction.
However, it's not easy to conclude that
"poor revving is due to a slightly dirty air cleaner."
Modern cars are electronically controlled, so a comprehensive check, including fault diagnosis, is necessary.
Cause 3: Throttle and electronic control
Most modern cars use an electronic throttle.
Instead of the accelerator pedal and throttle valve being directly connected by a cable,
throttle opening is controlled using information such as:
Accelerator operation.
Engine speed.
Vehicle speed.
Load.
Transmission.
Various sensors.
Therefore, it's not a simple relationship where
pressing the accelerator pedal 50% always opens the throttle 50%.
The ECU controls it considering factors like:
Engine protection.
Fuel efficiency.
Exhaust emissions.
Traction control.
Gear shift control.
Thus, depending on the car model, even in a normal state, you might feel that
"the RPM rises a bit slowly in response to accelerator input."
If it's been like this since before, it might be a characteristic of the vehicle.
On the other hand,
if it used to rev easily but suddenly changed,
then you need to investigate other causes.
Cause 4: Fuel injection and combustion condition
For the engine to rotate smoothly,
air,
fuel,
and ignition
must be combined in the proper state.
If there are problems with the fuel injection system or combustion condition, symptoms such as:
Unstable idling.
Hesitation during acceleration.
Uneven RPM increase.
Increased vibration.
may appear.
Related components include:
Injectors.
Fuel pump.
Fuel pressure system.
Airflow 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 important.
Cause 5: Engine oil condition and viscosity
Inside the engine, numerous parts move at high speeds.
Engine oil properly manages their friction.
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 is not always better, nor is lower viscosity.
The manufacturer specifies it to match the engine design.
For example, for an engine specified for 0W-20, simply choosing a significantly different viscosity solely because you think
"higher viscosity seems like it would protect the engine better"
is inappropriate.
Conversely, choosing an extremely low viscosity that is not 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 a 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 lightly."
Ensuring the necessary oil film and lubrication performance is a fundamental prerequisite.
It is important to use the manufacturer-specified viscosity appropriate for your vehicle model, engine, and operating environment.
Cause 6: Cold engine
The condition of the engine differs immediately after starting and after warming up.
When cold,
engine oil viscosity,
fuel injection control,
idling control,
and the temperature of various parts
are different from after warming up.
Therefore, even if the engine's rotational feel seems a bit heavy immediately after starting, it's not necessarily an abnormality.
This difference is particularly noticeable in cold weather, such as during winter.
It is important to compare it with the state after the engine has fully warmed up.
However, if obvious abnormalities persist even after warming up, an inspection is necessary.
Cause 7: Exhaust system resistance
The 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 is an abnormality in the exhaust system and exhaust gases cannot flow normally, it can affect engine performance.
For example, if exhaust resistance increases extremely due to an abnormality inside the catalytic converter, it can lead to symptoms such as:
Difficulty revving up to high RPMs.
Lack of power under load.
Difficulty exceeding a certain RPM.
However, since the exhaust system operates at high temperatures, 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
Various frictions occur inside the engine.
For example:
Piston rings and cylinders.
Crankshaft bearings.
Camshaft.
Valve train.
Chains and belts.
Oil pump.
Friction itself is not an abnormality.
In fact, some contact and oil film are necessary for the engine to operate normally.
What is important is
whether it is in the designed and appropriate state.
If there is insufficient lubrication,
abnormal wear of parts,
bearing malfunction,
or oil management issues,
rotational resistance may increase.
However, such internal conditions cannot be diagnosed solely by the "feel of revving."
If accompanied by unusual noises or oil pressure warnings, it is important to stop driving and have it inspected.
Auxiliary component resistance can also be a factor
The engine doesn't just spin the crankshaft.
Depending on the vehicle,
alternator,
air conditioner compressor,
water pump,
and various other pumps
are also driven.
When you use the air conditioner, you might feel that
the engine load increases slightly,
or the idling sound changes,
which is related to the load from these auxiliary components.
Normally, the ECU corrects this, but if there is abnormal resistance in the auxiliary components, it can affect the engine feel.
In turbo cars, boost also plays a role
In turbo engines, the boost condition also affects the impression during acceleration.
Turbochargers compress intake air using the energy from exhaust gases.
Therefore, if there are problems with the
intake system,
exhaust system,
boost pressure control,
intercooler,
or piping,
the engine may not produce its full torque.
In this case, you might feel that
the engine itself isn't revving,
or rather, it lacks power under load, which results in poor revving.
You might feel "poor revving" due to AT or CVT influence
Even if there are no actual engine problems, the way the engine revs up might feel different due to the transmission control.
In ATs,
engine speed changes due to upshifts,
kick-downs,
and lock-ups.
In CVTs, by continuously changing the gear ratio, the engine tries to maintain an efficient RPM range.
Therefore,
the way the engine revs up might feel different compared to a manual transmission car you used to drive,
or the impression might differ between sport mode and normal mode.
It's important not to conclude that there's an engine malfunction based solely on the "revving" sensation.
Can I tell by revving in neutral?
To check how the engine revs, you might think
"I can tell by revving it in P or N."
However, this alone cannot provide an accurate diagnosis.
The load on the engine differs greatly between an unloaded state and while driving.
Furthermore, in modern cars, some models have control systems that limit engine speed in P or N range.
Therefore, you cannot conclude it's a malfunction simply because
it doesn't rev up to high RPMs in P or N.
It's important to avoid unnecessary revving and follow the manufacturer's owner's manual and maintenance standards.
Be cautious if it "doesn't rev up to high RPMs"
If the issue is beyond just a slightly heavy revving sensation, and involves:
Not being able to rev beyond a certain RPM at all.
The engine warning light being on.
Severe vibration.
Obvious misfires.
Unusual noises.
A sudden increase in black or white smoke.
A burning smell.
A water temperature warning.
The oil pressure warning light being on.
In such cases, it's best not to consider it a normal "poor revving" issue.
There's a possibility that a fail-safe control is activated to limit output for engine protection.
Do not continue driving; consult a dealer or repair shop.
What to check first when the engine revs poorly
If you notice an abnormality, first organize the differences from before.
When did it change?
Is it only when cold?
Does it persist after warming up?
Is it only at low RPMs?
Does it not rev well at high RPMs?
Does it change with the AC on or off?
Is the warning light on?
Are there vibrations or unusual noises?
Have you had an oil change recently?
Have any parts been replaced recently?
This information will help the repair shop diagnose the cause more easily.
Check basic maintenance
If there are no clear fault symptoms, it's important to start by checking basic maintenance conditions.
For example:
Engine oil change interval.
Oil level.
Specified viscosity.
Air cleaner.
Spark plugs.
Other periodically replaced parts.
In particular, spark plugs are consumables.
After extended use, the electrodes can wear, and the spark gap can widen, potentially leading to misfires.
Replacement intervals vary depending on the vehicle and plug type, so check your owner's manual or maintenance records.
Will adding additives improve revving?
This needs to be considered carefully.
Engine oil additives and fuel additives each have different purposes.
However, it's not the case that
poor revving = adding an additive will fix it.
For example, if:
A spark plug is faulty.
There's a problem with the ignition coil.
A sensor is malfunctioning.
There's a problem with the catalytic converter.
There's an internal engine failure.
Additives cannot repair these conditions.
The first thing needed is to distinguish whether it is:
A malfunction.
A maintenance issue.
A characteristic of the vehicle itself.
Don't change oil viscosity just to "lighten the revving"
We also do not recommend
changing to an oil with a significantly lower viscosity than specified
just to make the engine rev lighter.
Oil viscosity is not determined solely by rotational resistance.
It is specified considering factors such as:
Oil film retention.
High-temperature protection.
Engine design.
Operating environment.
First and foremost, it is essential to use the manufacturer's specified viscosity and standard.
Regarding oil viscosity,
the article "What is the difference between 0W-20 and 5W-30?"
provides a detailed explanation.
Revving and friction loss
An engine cannot convert all of the fuel's energy into driving force for the wheels.
Inside the engine, some energy is lost due to:
Friction.
Pumping losses.
Auxiliary component drive.
One such loss is friction loss.
As frictional resistance increases, a larger proportion of the force generated by combustion is used to turn the engine itself.
Therefore, friction and lubrication are important themes when considering the engine's rotational feel.
However, it cannot be concluded that
"poor revving = 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, the condition of its:
Tires.
Oil.
Ignition system.
Intake system.
Drivetrain.
changes.
Also, as the driver becomes accustomed to the car, they may become more sensitive to changes than before.
What is important is:
Did it change suddenly and significantly?
Did it change gradually?
Are other symptoms present?
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 described by just
maximum power
and maximum torque.
When actually driving, there's a certain "feeling" that encompasses:
Smoothness of rotation.
Response when pressing the accelerator.
Vibration.
Sound.
Naturalness of RPM increase.
And behind this feeling are multiple factors, including:
Combustion and fuel.
Friction and lubrication.
Electronic environment.
Mechanical condition.
At Next Science, we don't just focus on simply adding something to increase maximum output.
We consider "driving quality" from the perspective of:
Where energy is generated.
Where it encounters resistance.
How it is transmitted.
Engine revving is one element that helps us feel this vehicle condition.
Summary: Poor revving has multiple causes
Engine revving generally refers to the sensation of how engine RPM increases in response to accelerator input.
Possible causes for poor revving include:
Spark plugs and ignition system.
Intake system.
Electronic throttle and control.
Fuel and combustion condition.
Engine oil.
Cold engine conditions.
Exhaust system.
Internal engine friction.
Auxiliary components.
Turbocharger/boost system.
Transmission control.
The important thing is not to jump to a single conclusion.
First, check:
Is it only when cold?
Does it persist after warming up?
Is it at low or high RPMs?
Are there warning lights or vibrations?
Has basic maintenance been performed?
If it is accompanied by:
Warning lights.
Severe vibration.
Unusual noises.
Smoke.
Unusual odors.
Obvious misfires.
Rapid performance degradation.
then do not try to fix it with additives or self-diagnosis; have it inspected by a dealer 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 use special methods.