Photograph by Hyoung Chang, Denver Post, Getty Images
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Drivers who are interested in boosting fuel economy have more options in a world of increasingly computerized cars. Here, a hypermiler uses a gauge mounted near the speedometer to measure mileage.

Photograph by Hyoung Chang, Denver Post, Getty Images

You Can Hack Your Car for Better Mileage—But Should You?

As auto computers get more sophisticated, so do the options for tweaking them.

Thanks to the Volkswagen scandal, you probably know that your car's computer system can determine a lot about the ride—including whether it's legal.

The automaker infamously tweaked its software to cheat emissions tests. If that's possible, could drivers optimize those same systems to save fuel?

The short answer is yes, but you might want to think twice before doing it.

Auto electronic systems are getting ever more elaborate, Tesla's airplane-like Autopilot feature being the latest example. Car enthusiasts fiddle with them all the time. Some are hypermilers who use a whole array of techniques to squeeze more mileage out of regular cars; most just want to boost driving power.

Either way, if you want to try it yourself, be prepared to pull out your reading glasses.

Company engineers spend hundreds of hours programming the settings that dictate how a car runs, says Robert Leale, a consultant and car software expert based outside of Detroit, Michigan.

The car's main computer, the Engine Control Unit (ECU), stores a complex configuration meant to balance the amount of driving power needed with fuel efficiency requirements. Among other variables, it regulates the ratio of fuel and air sent to the cylinder, the timing of fuel combustion, and the amount of boost from a turbocharger.

"It's a very big challenge. even internally, in the company itself," he says, noting that he's met engineers who fine-tune settings just by feeling and listening to an engine's purr. "I think it's an art form."

But as any car nerd knows, "automakers left something on the table when they shipped the car" in terms of both power and fuel economy, says Damon Lavrinc, a former auto journalist and head of content at Automatic, a San Francisco-based maker of apps for drivers.

Any car can run harder; conversely, it can be leaner on fuel. Automakers strike a balance meant to satisfy drivers while meeting efficiency standards, backing up warranties, and ensuring long-term reliability.

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The holders of the Guinness World Record for lowest fuel consumption in the contiguous United States in a non-hybrid car did it in a Volkswagen: Drivers Bob Winger, left, and Wayne Gerdes, stood with their 2013 Passat TDI two years ago.

When Volkswagen couldn't strike that balance with its diesel models, it cheated, turning on pollution controls only when the car was being tested electronically, and shutting them off otherwise.

Sporty drivers and hypermilers alike go after that wiggle room in the engine programming. When it comes to the software, there are generally two ways to go about it: break into the system's code and figure out your own customization, or buy devices that will load presets in for you, sort of like sound modes on a stereo.

The possibilities have given way to a cottage industry, from engine-tuning companies that brand their own car builds to chipmakers that sell plug-in settings. Austin, Texas-based Cobb Tuning, for example, sells devices ranging from $500 to $1,200 that plug into your car's diagnostic port and remap the ECU.

Earl Schexnayder, who customizes motors in southern Louisiana, says that tweaking a car's software can get three or four extra miles to the gallon, depending on how you drive. Especially while gas prices are low, it's hard to imagine anyone but the most diehard efficiency enthusiasts taking the time and money for such modest gains.

Both professional and amateur tuners must confront the security measures that most automakers layer onto their programming. "The manufacturers don't want you to change these calibrations," Leale says, because they fear warranty disputes and safety issues. Car hackers had a victory recently when the Library of Congress Copyright Office said that auto software is exempt from protections, clearing the way for tinkering without fear of a lawsuit.

But digging into your car's electronics can come with unintended consequences. Schexnayder says he's seen lots of people "screw it up pretty good" when they try to tune an engine themselves, adding that the process requires special tools and calibration: "It's definitely not a do-it-yourself deal."

Even buying settings from a reputable dealer can potentially shorten the life of certain components and complicate repairs down the road. A sales rep at Cobb says the company doesn't offer warranties on its engine maps, and that using them in most cases "would probably void the [manufacturer's] warranty."

There's another, counterintuitive effect, one the U.S. Environmental Protection Agency noted in its comments to the Copyright Office: Tuning an engine to use less fuel results in higher emissions, because it hampers the catalytic converter's ability to clean the exhaust.

"Fuel economy does not equal better for the environment, always," Lavrinc says. "If you change these very carefully crafted parameters, yeah, you might eke out a few extra miles per gallon, but you don't know what kind of emissions you're spewing," or what kind of wear and tear you're creating.

Both Lavrinc and Leale say that there are better, easier ways to save on fuel. Companies such as Automatic and Garmin make apps that can help drivers track mileage and fuel use. That said, most of the tried-and-true ways to save don't involve screens or settings: properly inflated tires, a mostly empty trunk, and good driving habits all contribute to more efficiency.

Lavrinc suggests keeping your vision focused well down the road, for example, as hard braking ends up using more gas than coasting to a stop: "These small changes to driving habits actually have a much bigger effect on fuel economy than most people realize."

The story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.

On Twitter: Follow Christina Nunez and get more environment and energy coverage at NatGeoEnergy.