Saving fuel with a car’s VVT-i system

If your engine oil has not been changed on schedule, it could damage the VVT-i system. Change engine oil as recommended by your mechanic or the car manufacturer. Courtesy Photo

What you need to know:

Using a VVTi correctly can save a driver up to 20 per cent fuel compared to non-VVTi engine. However using VVTi incorrectly could waste 30 per cent of fuel compared to non-VVTi engine. So it is a double edged sword

It is obvious that with the change in technology not all engines are designed the same. According to Thomas Kayinja, a mechanic at Grace Lubega Motors in Makerere, the more advanced the engine, the more power the engine can deliver while maintaining lower emission and lower fuel consumption. In this article, we will use Toyota’s VVT-i engine to represent a modern engine, since it is the most commonly used valve timing technology.

Lately people think that the word VVT-i is just a marketing gimmick and this has been proven by car dealers who use this as so. However Kayinja says they are wrong. He says according to the test he carried out, using VVT-i correctly, the driver could save up to 30 per cent fuel compared to non VVT-i engine. However Kayinja says in the same way using VVT-i incorrectly could waste 30 per cent of fuel compared to a non VVT-i engine.

Engine characteristics
According to Kayinja, the first thing to do is to study your engine’s characteristic. He says usually, a VVT-i engine will change its timing between low engine speed and high engine speed at around 3,000 RPM (Revolutions per minute). For clarity on the gauge, labeled RPM or r/min, this tells drivers how fast the vehicle’s crankshaft is spinning as the vehicle accelerates or decelerates. Drivers should then try to find the difference between low speed timing and high speed timing. Usually you will feel that the car accelerates faster at that RPM.

You will then need to check the lowest RPM that your engine can work to move your car on a straight and level road. Usually, it will be near 2,000 RPM and this is where VVT-i comes in. It could deliver 90 per cent of its torque from RPM as low as 2,000.

How to drive
Then you will need to change your driving habit. To drive quickly you will need to press the throttle which controls the speed of an engine or the flow of fuel in the engine quickly but then shift up just under the engine’s timing change RPM. So, if your engine’s timing change RPM is at 3,000, you will need to shift at 2,950.

Usually the engine and transmission is designed to work together so the RPM could drop to just above the lowest RPM to move the car comfortably like from 2,950 to 1,900. This will preserve the car’s swiftness and save fuel. Kayinja says the higher the RPM, the more horse power your engine delivers and the longer you stay at high RPM the more energy you waste. The quicker you press the throttle the quicker you reach desired RPM and this results in quicker shift to the next gear.

This will reduce the time required to reach the desired speed, so the consumption variable will be small. Using lower RPM means lower average power output from the engine, therefore reducing the power variable of the engine. With all these reducing the fuel consumption will go down as well.

Kayinja says the difference with old carburetors and VVT-I is that the old carburetors engine tends to waste fuel when accelerating quickly but the VVT-i with injection engine will only use the needed fuel, in milliliters precisely. However Kayinja says if a VVT-i engine is used incorrectly, it will waste more fuel. This is because VVT-i engine delivers more power compared to conventional engines at higher RPM’s.

Signs of VVT-i engine failure
Thomas Kayinja, a mechanic at Grace Lubega Motors, says common signs include the check engine light coming on, dirty engine oil, rough engine idle, and a decrease in fuel economy. Most cars today have an ECU which monitors virtually all components. When one part is beginning to fail, the ECU will generate and store a specific fault code which at the front end shall illuminate the check engine light indicating problem exists.

Tips on how to save fuel while driving
Drive at normal speed
In freeways, the fuel consumption when driving under and above 100 km/h are very different. Sudden acceleration and braking can consume 40 per cent more of your energy. Instead of continuity braking and accelerating, understand the traffic in front and remain at normal speed.

Check tyre pressure
It is recommended to check your car tyre pressures at least once every month. The lower the pressure, the more gas the vehicle needs to move on the road. Good tyre condition is a requirement for energy saving, since it helps the engine runs smoothly.

Avoid too much weight
A car is like your body: it requires more fuel to carry more weight. With every 50 kilo of luggage, it will consume two per cent more fuel than normal. So if it is unnecessary, drivers should avoid carrying many heavy items.

Keep air filter clean
It is important for car owners to check air filter condition regularly, since a broken air filter will consume 10 per cent more energy. In order to check this car part, drivers can examine it after washing it carefully. If the sunlight can go through the air filter, drivers should change to a new one. If the filter gets congestion regularly, it is also suggested to replace a new air filter to make sure the air purification is clear and fuel is saved.

Switch engine off
When the vehicle stops or is not working for a long time, it is wise to shut down the engine to reduce unnecessary gas consumption. It is also to avoid heating the engine for too long, which also affects the environment.

Turn off AC
If the weather is comfortable, it is advisable to turn off the air conditioner. This enables fuel efficiency since the car AC usually consume 10 per cent of the energy.
However, at the speed of 80 km/h, using air conditioner is better for your vehicle than opening the window.