Practical primer on EFI, diesel, propane, compressed natural gas and electric zero-turn mowing

It was hot. The little bit of coolness that had greeted the crush of rush-hour pedestrians had, by 10:30 a.m., been baked away, with not so much as a wisp of a cloud in the sky. This late June day in Washington, D.C., promised to be a scorcher. Even so, the National Park Service Going Green event at the Jefferson Memorial had to go on. The functionaries for the event, seemingly impervious to the morning’s oppressive humidity and heat, came dressed in business suits and in the case of Robert “Bob” Vogel, superintendent National Mall and Memorial Parks, in full park service uniform and wide-brimmed hat.

Fittingly, the event, which had the distinct feel of a coming out party, previewed the marriage of the two hottest trends in commercial mowing technology—propane-fueled commercial mowers featuring closed loop electronic fuel ignition (EFI) engines. About 40 well-dressed spectators sat attentively in metal folding chairs and politely listened as Vogel, Ron Flowers, executive director of the Greater Washington Region Clean Cities Coalition, and Roy Willis, president and CEO of the Propane Education and Research Council, gave short presentations extolling the National Mall’s commitment to “green” goals and the role of six new EFI, propane-fueled Exmark mowers in advancing those goals.

Then, after a ribbon-cutting ceremony, prim and attractive WUSA-TV personality Andrea Roane ordered the six shiny Lazer Z S-Series zero turns to action on the football-field size lawn in front of the Jefferson Memorial. The dozen or so videographers and photographers seemed to take no notice that the mower operators, speeding back and forth across the lawn, weren’t actually cutting grass.

In the turf management industry (one dominated from its founding by carbureted gasoline-powered equipment) the sun is indeed shining on EFI (in this particular case on Kohler closed loop EFI engines) and propane fuel.

PERC, the National Park Service and representatives from the Kohler Company and Exmark were on hand for a media event lauding the donation of six propane-fueled mowers with EFI engine options.

That the two are now paired on Exmark Lazer Z S-Series mowers was described by participants at the event as being a huge step forward in reducing both fuel costs and emissions at the National Mall and, by extension, for other grounds pros and commercial cutters. While Exmark has exclusive rights to the technology this year, other manufacturers are likely to begin offering their own EFI propane models in 2014.

“The commercial market is going to be impacted significantly. Users can see as much as 50 percent off their fuel costs” with EFI propane, said Martin Radue, senior staff engineer at Kohler at the event. He said that most of the components for adapting EFI to smaller gasoline-powered engines have been in place for more than a decade and used in engine applications for a range of vehicles—mowers, motorcycles and golf carts, to name just a few.

Walker Manufacturing, Ft. Collins, Colo., is credited with being the first mower manufacturer to offer EFI gas-powered commercial products. This was less than a decade after the U.S. auto industry in 1991 completely phased out carburetors in favor of EFI. The last domestically produced carbureted car was the Ford Crown Victoria Police Interceptor with a 5.8-liter, 351-cubic-inch engine.

“As for EFI for propane, we had to wait for the components to be developed first,” said Radue. “We had to wait for that part of the industry to mature more in order for us to adapt it into our systems.”

Added Kohler’s Brandon Fredericks, market analyst Global Power Group: “Now that end users are experiencing a large financial benefit we’re starting to see them swapping out their entire fleets.” He said that owners operating many mowers, in particular, may see their fuel costs cut in half with EFI propane because they will have bargaining power with propane suppliers.

Gas still king

In spite of the seemingly endless string of favorable media reports about propane as a small engine fuel for mowers (with or without EFI), the $15 billion outdoor power equipment industry is still dominated by gasoline. That’s not likely to change soon given the industry’s size, its fragmented nature and the convenience of using gasoline. More than 160,000 retail establishments across the United States sell gasoline.

Other equally important factors favoring gasoline as the industry’s fuel of choice include the lower upfront cost of gasoline engines (EFI are more costly than carbureted models) and the strides being made in the development of gas-powered engines. Today’s gasoline engines, thanks to EFI in particular, are significantly more fuel-efficient and have reduced emissions by as much as 75 percent from similarly sized engines produced in the mid-1990s.

“Often they (customers) ask about the price upfront,” in regards to mowers with EFI engine options, said Mike Cromley, marketing manager for Walker Manufacturing. “That can be a deterrent to buying. However, if OEMs can effectively show how a commercial operator can truly save and make money even with a higher upfront cost, it would be more beneficial for customers.”

Cromley said an EFI gas engine represents a fuel savings of at least 25 percent compared to similar-size carbureted gas engine so realizing the savings versus the upfront costs can happen in about a year.

“Add into that performance, reliability and clean running emissions, and the equation becomes more palatable versus carbureted engines,” he added.

Closed Loop Versus Open Loop EFI

An EFI system is a computer-controlled fuel delivery system with an electronic control unit (ECU) that reads sensors located on the mower and makes the determination of how much fuel to allow the engine to have based on RPM, engine temperature, air temperature, throttle position and other vital information. The sensors provide information on operating conditions and load on the engine.

EFI engines are 25 percent more fuel efficient, meaning they mow longer with less downtime. They’re easier starting (no choke), and they also produce 25 percent less emissions.

There are two types of EFI in today’s mowers—closed loop and open loop EFI. Both use ECUs to control the amount of gas that’s injected into the cylinders. The key difference between the two is how the ECU determines how much gas is needed.

Closed loop: In the closed loop system the ECU controls the amount of fuel injected into cylinders based on a 2D “map” of engine RPM and load. It provides up to 25 percent efficiency gains, provides easy starting and lower emissions.

  • ECU reads engine RPM and unused oxygen
  • Fuel pump pressurizes fuel and sends fuel into injectors
  • O2 sensor measures unused oxygen in the exhaust (engine load)

Open loop system: In the open loop system the ECU controls the amount of fuel injected into cylinders based on engine RPM “map”. It’s less expensive than the closed loop system but also offers easy starting and efficiency gains, although less than those provided by closed loop EFI.

  • ECU reads RPM
  • Fuel pump pressurizes fuel and sends fuel to injectors
  • Injectors inject fuel into cylinder

Source: Mutton Power Equipment, Fort Wayne, Ind.,

Commercial cutters are responding, judging by the number of new products coming to market. This past July, Grasshopper, Moundridge, Kan., was the latest manufacturer to introduce new EFI zero-turn mowers, its MidMount 327 EFI and its FrontMount 727KT EFI, both with second-generation, 747cc Kohler Command Pro engines.

“These EFI engines are continually monitoring internal and external factors that can affect engine performance, such as fuel grade, fuel quality, ambient air temperature and altitude and making automatic adjustments to optimize performance, increase fuel efficiency and extend service life,” said Ruthanne Stucky, marketing manager at Grasshopper.

Deere’s Z925M Flex Fuel EFI Mower accepts E85 for lower fuel costs.

Both propane and gasoline offer their own unique advantages in fueling America’s huge mowing fleet, but so do other fuels, such as diesel.

Diesel offers advantages, too

Several major mower manufacturers offer rugged diesel-powered commercial mowers. While the market share of diesel units is small compared to similar-sized gas models, and they don’t command the media attention that has been focused on propane these past five years, they’re often the wisest choice for many contractors.

Because diesel engines provide more torque than gas or propane engines, they’re better able to power through wet or tall grass, and can put more muscle into chores, such as vacuum collection. This power advantage is significant, as much as 50 percent more gallon-for-gallon compared to propane—more power means more work done, according to the Grasshopper Company. Grasshopper offers a Diesel Fuel and Emissions Calculator on the website ( in support of its claims.

Also, as far as emissions, technological advancements have removed many of the harmful particulates in diesel fuel making it cleaner than ever, especially in today’s EPA Tier 4 Final-compliant diesel mowers, it notes.

Deere’s new flex fuel machine

One of the most recent innovations to meet the rapidly changing U.S. fuel market is John Deere’s new Z925M Flex Fuel mower.

“Our customers continue to look for alternative fuel platforms and for ways to decrease operating costs,” said Steve Wilhelmi, tactical marketing manager, John Deere Commercial Mowing. “With components specifically designed and tested for use of E85 gasoline, this mower offers fuel flexibility as the demand for E85 continues to grow.”

He says the Z925M Flex Fuel mower offers customers three main benefits: Improved horsepower and fuel efficiency via a closed loop EFI system; fuel blend choices ranging from zero to 85 percent ethanol; and about 40 percent lower green house gas emissions than gasoline.

“Commercial customers will look at the E85 gasoline prices to decrease their operating costs,” said Wilhelmi. “Governmental agencies are interested in the environmental benefits of a flex fuel machine.”

Wilhelmi added that stale or contaminated fuel is often the cause of fuel-related problems in small engines. Use fresh, clean fuel purchased in a quantity that can be used within 30 days and add fuel stabilizer with each fuel purchase, he advised.

Compressed natural gas

Compressed natural gas (CNG) is also a proven technology that has been around for quite some time, but the development of CNG as an alternative fuel for mowers didn’t happen until recent years. Dixie Chopper was one of the first manufacturers to introduce a CNG-powered zero-turn mower with the release of its Eco-Eagle model in 2010. (By comparison, its first propane model was launched in 2006.)

Toro’s Professional 5000 and 6000 closed loop EFI While carbureted mowers still outsell those with the EFI engine option, the momentum in favor of EFI is growing. Toro offers EFI on its Professional 5000 and 6000 Z Master models.

Similar to propane, commercial cutters can convert their existing gas-powered engines to run on CNG, rather than buying new. The other advantages are also comparable. CNG is an abundant natural resource that’s cheaper than gasoline and burns much cleaner. It is also safer, since CNG is lighter than air and disperses quickly into the atmosphere in the event of a release.

The adoption of CNG has been slow. The main deterrent is the lack of infrastructure for refueling, as CNG stations are few and far between.

Everyone that we spoke to in researching this article advised contractors (because of today’s intense competition and thin mowing margins) to review their markets’ mowing requirements, and to thoroughly examine product claims and crunch their numbers before making significant equipment purchases.

Also, keep in mind the regional and fragmented nature of the commercial mowing market.

While contractors with large mowing fleets and the capital to install fueling stations for, say, propane and can negotiate bulk fuel purchases, smaller operation, the owners of most smaller operations remain satisfied with pulling up to the local convenience store, filling up gasoline or diesel, and grabbing a coffee.

Fuel costs, fuel efficiency, fuel availability and, in some markets, emissions figure heavily into these calculations and, ultimately, a company’s profit picture. Choose wisely.

Ron Hall is editor-in-chief of Turf magazine. He has been researching and writing about the green industry for 29 years. Reach him at [email protected].