From March 1, stricter emissions testing procedures are being implemented at vehicle registration centers nationwide. Many car owners are concerned about the "flooring the gas pedal" component of the idle test for diesel cars, questioning its potential impact on the engine.

According to Anh Tuan, a technical expert from a Japanese car manufacturer in Vietnam, most modern automobiles have an idle rev limiter to keep the engine within safe operating limits. For example, if a car has an idle rev limit of 3,500 revolutions per minute (rpm), flooring the gas pedal will not cause the engine to exceed this threshold. The specific engine speed limit can vary depending on the manufacturer and the car's technical specifications.

If the gas pedal is fully depressed while idling and the car has a rev limiter, the engine will not experience any issues. However, for vehicles without a rev limiter, flooring the gas pedal can cause the engine's rpm to surpass the manufacturer's design limits during idle, potentially leading to serious engine damage.

Associate Professor, Doctor Do Van Dung, former principal of Ho Chi Minh City University of Technology and Education and currently Vice Chairman of the Ho Chi Minh City Automobile - Engine Association, stated that for well-maintained vehicles and correct operating procedures, briefly increasing engine speed at idle (for a few seconds) causes no significant harm to the engine. He considers this a "health check" for the engine when it is not under mechanical load or moving.

However, experts note that some factors, though rare, could lead to risks if the car is not in ideal condition and the engine speed reaches high or maximum thresholds, even for vehicles with an idle rev limiter. Firstly, if the engine is not warmed up, the lubricating oil may not have reached its optimal viscosity, leading to poor lubrication and potential wear on pistons, piston rings, and camshafts during sudden acceleration.

Additionally, for diesel cars using turbocharger technology, rapidly accelerating to the rev limit and then suddenly shutting down the engine can interrupt the lubricating oil supply to the turbocharger. The turbocharger's shaft, which spins at high speeds, does not stop immediately due to inertia when the engine is turned off. Without adequate lubrication, the shaft of this component can experience wear and damage.

For cars that are used infrequently or do not have regular oil changes, the risk to the engine is greater. Old oil can reduce lubrication efficiency, potentially causing minor damage to components if the engine speed increases significantly.

If a car has dirty spark plugs, fuel injectors, or an air filter, or a faulty oxygen sensor, it may experience a loss of power, backfire, or strong vibrations during acceleration. This puts stress on the pistons and crankshaft.

In diesel cars, if the governor malfunctions, the rpm could exceed safe limits (e.g., above 4,000-5,000 rpm) when idling. This can trigger an engine damage warning.

A car undergoing inspection at a center in TP HCM. Photo: Thanh Nhan

Older cars with weaker engines might experience "fuel flooding", emit thick black smoke, or even suffer valve damage if accelerated too suddenly without a rev limiter.

To protect their vehicles and meet inspection requirements, Vietnam Register and other experts recommend that car owners adhere to the manufacturer's maintenance schedule. Before each emissions test, it is essential to check and replace (if necessary) components such as fuel injectors, combustion chambers, catalytic converters, and air filters. It is also crucial to use standard fuel to ensure stable engine operation. Before bringing a car in for an emissions test, the engine should be warmed up for about 10-15 minutes.

The process for car emissions testing from March 1.

Nguyen Quoc Thinh, deputy director of the 5003V registration branch in TP HCM, stated that in addition to the guidelines from Vietnam Register, inspectors' judgment based on experience and unusual signs, such as engine jerking or knocking sounds from the engine compartment, can also alert car owners to the risk of damage if a free acceleration test, involving fully depressing the gas pedal, is conducted.

"To prevent risks, especially for cars without a rev limiter or those showing abnormal engine signs, inspection facilities either require the owner to sign a commitment or advise them to take the car for maintenance and repairs to ensure optimal condition before returning," Thinh added.

Pham Trung