Mercury EFI Technology

Jun 19, 2024
What is Electronic Fuel Injection?

This technology makes modern marine engines possible

Today’s smooth-running, easy-starting, low-emission and fuel-efficient marine engines would not be possible without electronic fuel injection (EFI). Once a feature found only on more exotic high-performance engines, EFI systems began to appear on mass-produced automobile and powersports engines in the 1980s. Mercury Marine introduced its first EFI production outboard, the V6 Laser 220, in 1987. Today, most Mercury outboard models from 8hp to 600hp are equipped with an EFI system. Here’s a quick look at how EFI works.

How EFI Works

Electronic fuel injection replaces a carburetor on gasoline engine. A carburetor introduces fuel to the airstream, which flows into the engine as the air is accelerated through a venturi tube. While a carburetor can be made to function well, EFI offers many advantages. An EFI system uses a nozzle, or injector, to deliver a mist of pressurized fuel to the engine, either into the airstream flowing into the engine or directly into the cylinder. Modern Mercury engines have a multi-port EFI system, which places an injector for each cylinder in the intake manifold.

The injectors are controlled by an Engine Control Module (ECM), a compact computer that gathers data from sensors that monitor the oxygen level of the exhaust, the coolant temperature, the throttle position and engine RPM, as well as environmental factors such as air temperature and barometric pressure. The ECM then adjusts fuel delivery and engine spark timing to achieve optimal performance. For example, fuel and timing can be adjusted for best economy at cruising speed, for maximum power on hole shot, for a turn-key start when the engine is hot or cold, and for changes in temperature and elevation. No carburetor can match the precision of a modern EFI system.

Mercury Battery-Free EFI

Like any computer, the ECM requires electrical power, which is supplied by the boat batteries. This excludes EFI for manual (rope) start Mercury portable outboards. Up until 2018, these engines didn’t require a battery. That’s when new twin-cylinder Mercury FourStroke 15hp and 20hp motors with a battery-free EFI system were introduced.

This system is now offered for 8hp to 30hp models with manual start. The motor uses its own charging system to energize the ECM when the starting rope is pulled. This system retains the battery-free portability that makes these compact outboards popular while incorporating many of the EFI advantages. If you have ever pulled the cord on a manual-start carbureted outboard over and over and over in a bobbing boat in the hot sun, you will certainly appreciate the ease of boating with a Mercury EFI portable. Also, because the EFI system is sealed and pressurized, it eliminates most fuel-related reliability issues. So, no more gunked-up carburetor after a few weeks of inactivity.

To learn more about the technology behind a Mercury outboard, visit a Mercury Authorized Dealer or go to

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