Is direct injection more trouble than it’s worth?
Direct fuel injection is creeping into more mainstream vehicles these days and it can have an inherent fault we need to be aware of.
What is direct injection? Direct fuel injection on gasoline engines sees the fuel injector mounted on the cylinder head to spray fuel directly into the combustion chamber. Its predecessor, port injection, had the injectors mounted in the intake manifold and the fuel spray was directed at the back of the intake valves.
Why the change? Direct injection technology provides slightly more power and better fuel economy (depending on the application, it’s usually in the range of 10 to 15 per cent improvement). But engine torque delivery can be bumped by as much as 50 per cent.
What’s the problem? On certain engines the back of the intake valves and their ports can become coated with carbon deposits. On the older style port-injection systems, the spray of fuel directed onto the valves kept this from happening, as modern fuels contain cleaners. If enough carbon builds up it can cause rough idling, stumbling on acceleration, stalling, check-engine lights, increased fuel consumption and a general lack of power. Some drivers have experienced this with well under 50,000 km on the engine. Short trips that don’t allow the engine to see any significant time at full operating temperatures can aggravate this condition.
What’s the cure? It depends on the amount of the buildup and its hardness. In some cases, a chemical liquid introduced into the intake, such as Sea Foam, can clean things up. It’s a relatively easy process where a port vacuum line is used to suck the liquid into the intake ports while the engine is running. It does create a substantial amount of smoke from the exhaust, so it should only be done in well-ventilated areas. Many carmakers have issued new engine-management software to help alleviate this problem by changing the amount of time the intake valves are open and adjusting the ignition timing. Regular oil changes also help to keep the valve-control mechanisms moving freely. If your vehicle is affected, stop using fuel with any amount of ethanol.
What won’t help? Anything that involves using the fuel injectors to clean up the mess. This means gasoline additives or fuel injection purge treatments. As the injectors are nowhere near the build up and don’t spray onto the valves, these services are a waste of time and money.