Signs of a faulty VVT-i engine

Friday February 17 2017


By Mustafa Ziraba

Many cars today including the Toyota RunX, Toyota Allex, Toyota Raum, Toyota Vitz, Toyota Spacio, keyword being Toyota, specifically small fuel-sipping cars from the manufacturer. Whenever one is in the market for one, as a selling point brokers and dealers always mention, “it’s engine is VVT-i.” In other words, its fuel consumption is bound to move you from Kampala to Entebbe on not more than five litres of fuel. What exactly is VVT-i and what exactly does it do.

Before you can appreciate how important valve timing is, you have to understand how it relates to engine operation. Remember that an engine is basically a glorified air pump and, as such, the most effective way to increase horsepower and/or efficiency is at increasing an engine’s ability to process air. There are a number of ways to do this that range from altering the exhaust system, bolting on turbochargers or superchargers to upgrading to a more sophisticated fuel system or simply installing a less-restrictive air filter.

Since an engine’s valves play a major role in how air gets in and out of the combustion chamber, it makes sense to focus on them when looking to increase power and efficiency without necessarily increasing fuel consumption.
Varying intake valve open/close timing according to the operating conditions of the car improves engine performance and fuel economy. Without variable valve timing, valve timing was a compromise between the need to produce maximum torque at low to medium speeds, maintain idle stability and fuel economy.
Lule Donald a mechanical and production engineer at Nakawa Vocational Training Institute in great technical detail explained that continuously adjusting when the valves open and close yields significant improvements.

The ECU (Engine Control Unit) advances or retards the intake camshaft, changing when the valves open and close according to driving conditions. Most valve timing systems optimise valve overlap (Overlap is where both outlet and inlet valves on the same cylinder are open at the same time) under all operating conditions. By taking maximum advantage of this overlap, intake air volume is increased, thus torque and output are improved and at the same time, enhancing fuel economy.

Signs that your Variable Valve Timing is not working
Kabenge Isaac, a mechanic at Nakawa 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.
Dirty engine oil is more of a cause as opposed to a symptom. The VVT-i works best when the engine oil is clean and still holds its intended viscosity. If your engine oil has not been changed on schedule, it could damage the VVT-i system. To avoid this situation, make sure to have your engine oil changed out as recommended by your mechanic or the car manufacturer. Again rough idle and decreased fuel economy are symptoms rather than causes. Therefore, valve timing gives engines more output thus achieving more with less fuel thus better fuel consumption.