How EFI Boosts Your MPG

Updated May 23, 2012


Kohler’s V-Twin EFI engine

Electronic fuel injection is poised to displace carburetors on small engines and increase your mowings per gallon.

By Glenn R. Dinella

How has EFI evolved for use with mower gas engines?

While basic fuel injection began on diesel engines in the 1920s, and electronic fuel injection debuted in the auto industry in 1967, more recent technology has brought a closed loop system to the small engine industry.

Kohler Engines has been working to develop EFI technology since the mid-90s and eventually began replacing the carburetor on some of its small engines with a closed-loop electronic fuel injection system. Recent gas hikes have simply brought more attention to these fuel-saving engines.



Exmark offers its Lazer Z X-Series with a 29 hp EFI option.



“The technology originally came from the auto industry, as well as the motorcycle and UTV industry,” says product manager Mark Johansen, “as they also need to design for the off-road usage similar to what a lawn mower experiences.

“We used components developed by Delphi and other fuel systems manufacturers when designing the Kohler EFI engine.”

Prominent at the 2011 GIE+EXPO was John Deere’s introduction of the ZTrak Pro Z925 EFI, which offers a Kohler 27-horsepower EFI engine. Exmark introduced three EFI equipped models in 2010 and has added four more for 2012. Walker Manufacturing got on board with EFI right away, beginning in July 1998.

“We pioneered small engine EFI with the folks from Kohler and also Bosch automotive systems,” says Tim Cromley, marketing manager, Walker. “This is not a new program to us.”

How does EFI work?

While an engine equipped with electronic fuel injection is operating, an oxygen sensor in the muffler continuously monitors the composition of the exhaust gas, making adjustments to the air/fuel mixture being delivered to the combustion chamber. Unlike open loop systems, Kohler’s closed loop EFI system delivers the exact amount of fuel needed by releasing fuel sequentially to each cylinder at the optimum time. The system adjusts for all operating conditions and loads. Sensors are detecting unused oxygen in the exhaust and instantly directing the engine to vary the amount of fuel injected to ensure there is no excess fuel being injected.

“Expected payback period in fuel savings can be realized within the first year of ownership.”

“The engine also monitors atmospheric and manifold pressure and temperature, which affects injection and ignition timing for optimized power and combustion,” Johansen says.

What are the benefits of EFI?

Walker made its model MT26 (26-horsepower Kohler OHV V-twin engine) available with EFI 13 years ago and then added the MTL31 (liquid-cooled, 31-horsepower Kohler) six years ago.



Walker pioneered EFI engines in its lineup in the 1990s. Shown here, the new MBS 26HP.



“Of all our seven models, our most popular engine this year is the EFI engine,” Cromley says. “While EFI adds about $1,000 to the MSRP, we did an evaluation of EFI fuel savings, and you’ll make it back in about a year, maybe sooner, with current gas prices.” Cromley adds he hopes to offer an approximate $500 price break in coming months.

In John Deere’s case, the difference is approximately $500 at retail, and the expected payback period in fuel savings for commercial customers can also be realized within the first year of ownership, says Jamie Palmer, product manager, Commercial Mowing. “With the closed loop system, the engine checks for unused oxygen in the exhaust multiple times per second, and this means the engine can fine-tune the amount of fuel injected into the engine, resulting in up to 25-percent fuel savings in real-world use.”

It’s important to note this is not based on dynamometer lab-type testing, Palmer says. “This is based on real-world conditions with real professional landscape contractors.”

Johansen agrees with the 25-percent fuel savings estimate. “For the commercial cutter, that equates to more than $600 per year,” he says. He points out landscapers with multiple mowers in their fleets will see fuel savings add up quickly on their bottom line.

Exmark also estimates fuel savings “minimally at 25 percent,” says Daryn Walters, director of marketing. “You may experience even better savings depending on conditions.”



John Deere’s ZTrak Pro Z925 EFI utlizes a Kohler 27-hp engine.



“At $3.25 per gallon, you’re saving 98 cents per hour,” says John Swanson, senior product manager, Exmark. “Typically, our customers who are commercial cutters will mow 1,000-1,500 hours per year. In the South, it can be up to 3,000 hours.”

Because there is no carburetor and no chock, EFI engines have consistent and reliable startability, as the possibility of flooding the engine is removed from the equation.

Another benefit of EFI: “It gives better running temperatures, so your components end up in better shape,” Cromley says. “You don’t get heads warping, and you get a longer life out of the engine.”

Tests and customer experience with Exmark’s EFI mowers have shown that power output is more reliable, Walters says. “When you get into taller grass or tougher conditions, you typically experience engine ‘droop,’ but since EFI units pump more fuel to adjust to changing loads, you have more consistent power.”

What is the future of EFI?

“The increased customer demands for efficiency have brought this technology to market,” Palmer says. “We expect to see it proliferate in the future.”

While Kohler is still playing their cards close to their vest, Johansen says they are constantly working on more improvements in fuel efficiency for small engines.

“We believe this is the future of fuel. We’re not chasing alternative fuels. We believe EFI is the best alternative.”

He speculates EFI might find its way into handheld equipment such as trimmers and blowers in the future. “There are some research firms that specialize in fuel systems development working on lower cost fuel injection systems,” he says. “But with small handheld equipment, the market is so price sensitive it will likely be several years before we see EFI in those markets.”

“We believe this is the future of fuel. A lot of people want to talk about alternative fuels like propane. We’re not chasing alternative fuels. We believe EFI is the best alternative.”

Cromley compares the impact of EFI on the automotive industry and the environment. “Back in the 70s when everything ran on carburetors, huge brown clouds hung over our big cities,” Cromley says. “Then EFI came along in the early 80s and started burning fuel cleaner. With EFI, you get a better burn.”

“In simple terms, since the EFI engine uses less fuel, carbon emissions are reduced by the same amount,” Johansen says. “That 25-percent fuel savings equals 25 percent less carbon emitted.”

Walters adds one of the major reasons Exmark has aggressively pursued EFI technology is “the opportunity to be good stewards of the environment for the industry.

“Our customers will dictate the future of EFI with Exmark,” he says, “but we are confident it has a bright future.”

Cromley also believes municipalities enacting bans on gas engines during certain days to improve air quality will change their ordinances when they look at the hard data on EFI. “Because EFI burns so cleanly, it would be competitive with some of the alternative fuels,” he says. “We say you can still be green with gasoline.”

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