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I understand the basics of fuel injection; my Ford F-150 EcoBoost, however, is direct injected. What's the difference? – Jim

Traditional multiport fuel-injection systems use an in-tank pump to pressurize fuel and deliver it to each port of the intake manifold with a standard fuel injector.

Alternatively, the basics of direct injection are:

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An in-tank pump is used to lift the fuel out of the tank and deliver it to a second high pressure pump which pressurizes the fuel up to 2,500 psi. Unlike standard multiport injection, which delivers fuel into the intake manifold, direct injection delivers the fuel directly into the combustion chamber. This new injector has to withstand the heat and pressure of the combustion process, meaning these new injectors share little in common with their predecessors.

Since the fuel/air is no longer mixed in the intake manifold, engineers can achieve significant improvements in control and quantities of the fuel being directly injected.

These tighter tolerances aid fuel atomization, leading to significant gains in the combustion process, which ultimately increases economy and power.

Of course, with any developing technology there are downsides. One of the major problems is carbon buildup on the intake valves. With multiport engines, the fuel coming down the intake manifold effectively washes the intake valve as it passes it on its way to the combustion chamber. Direct injection engines lack this unintentional benefit and carbon builds up on the intake valve, causing misfires and the need for periodic decarbonization.

Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail globedrive@globeandmail.com, placing "Lou's Garage" in the subject area.

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