A few years ago marine engine manufacturers were happy just to introduce electronic fuel injection to the boating world. EFI technology had recently swept the auto industry, providing smooth, easy starts in any weather for car drivers around the country. But many said the computer element necessary to run the system couldn't withstand the marine environment, so boaters would be forever stuck with mechanically carbureted systems.

Not long after, the engineers developed specially sealed electronic control modules and electronic sensors that would allow them to function in wet and even salty conditions. At last, EFI for boaters was here. Today, MerCruiser is no longer satisfied with just getting EFI into boats. The company has set out to perfect marine EFI for a variety of uses by taking advantage of the two different EFI systems: multiport injection and throttle-body injection.

Neither MPI nor TBI technology is new, but as MerCruiser became more comfortable with them, they learned how to manipulate each system's strengths to fit different applications. Whether you're into runabouts or large inboard cruisers, MerCruiser has an EFI engine that's built to perform best in the situations you'll use it for the most.

In an MPI system, one injector sits just behind each intake valve and dispenses an exact spurt of fuel directly into the cylinder. The timing and volume of that spurt are once again determined by the ECM as it monitors a similar array of sensors. Since the each cylinder gets an exact amount of fuel, the system is even more efficient, and since the injectors are closer to the cylinder, the engine has greater throttle response. But an MPI system has yet another benefit: it allows flexibility in the air-intake system.

Because the air and fuel are not mixed, MerCruiser is free to manipulate the air-intake manifolds to maximize engine performance at different rpm. Currently, the company uses a tunnel-ram intake system and a cross-ram intake system, depending on the engine's intended use. An engine like MerCruiser's high-performance Black Scorpion uses a tunnel ram, since the long straight intakes create peak horsepower at the top of the rpm scale, therefore maximizing speed. Meanwhile, the 7.4- and 8.2-liter inboards the company is developing use the cross-ram manifold. This set-up gives them more power in the mid range, which is better for high load uses and boaters who don't usually operate at wide-open throttle.

Flexibility within the intake design also allows MerCruiser engineers to model an engine to fit a certain space. This has proven particularly helpful in the ski boat market, where low-to-the-water boats often have small engine compartments but demanding power needs. A mechanically carbureted engine tends to shrink that engine box even more, since the carburetor and air filter that necessarily sit on top of the block extend several inches above the engine. This often means sacrificing horsepower in order to achieve fit. But an MPI has no such intrusive projections. The carburetor is gone, and the air intake can be molded around the engine almost any way a designer can imagine. There's no more dead space around the carburetor, and you can fill your engine box with nothing but engine.

Even as MerCruiser makes your boat run better, it's looking for ways to make it run longer with less problems. The company realizes that people don't want to spend their leisure time doing engine maintenance, and while it can't eliminate the need for maintenance, it can stretch the time between service points. Cutting down the amount of time you have to spend in the engine room has become a company mission that once again shows off the strengths of EFI.

The new line of big-block inboards are a great example. The closed cooling system features a 500-hour coolant that's a marked improvement over the old 200-hour variety, and new platinum spark plugs won't have to be changed as often as standard plugs. A new fuel/water sensor indicates when you need to drain your filters, and it will be possible to get a helm display that provides vital engine information directly from the ECM. An executive at MerCruiser indicated that even more extensive maintenance-reducing measures are being developed for next years engines, but couldn't discuss details. "Suffice it to say," he conceded, "we're looking at ways to increase the robustness of the entire electrical and fuel system in order to stretch out the maintenance for the customer."

By refining the existing technology, MerCruiser has once again taken the lead with EFI. The company has found new ways to make an already good system work better, and that's an idea we can all benefit from.

For more information, contact MerCruiser, Dept. PMY, 3003 N. Perkins Rd., Stillwater, OK 74075. Phone: (405) 377-1200. Fax: (405) 743-5370.