Although driving behavior has the greatest impact on fuel consumption, there are some things that can be done to diesel engines to help with mileage improvements. One modification involves fine tuning an engine's electronics.
Today's medium duty diesel engines, like their heavy duty counterparts, are highly engineered power plants that incorporate electronics and computerization to optimize performance, fuel economy and emissions. Basically, the brain of the engine is the engine control module (ECM), also known as the electronic control unit (ECU). The central nervous system, if you will, is the sensors and harnessing located in the engine and throughout the rest of the vehicle that send information to the ECM.
The ECM interprets this information and, using fuel mapping technology, regulates the air/fuel mix by electronic fuel injection (EFI) to keep the engine operating at peak efficiency. Fuel mapping takes into consideration a number of conditions that are measured by sensors. These include vehicle speed, air intake, atmospheric conditions, throttle and boost.
To reprogram a diesel engine, to put it simply, a computer is connected to the ECM and changes are then made to its software. There are, however, limits to what adjustments can be done so as not to affect the engine's ability to comply with emission standards and to not "overstress" powertrain components.
"One of the key advantages that we brought to the market with the electronic engine controls is the ability to customize the programming to meet the operational needs of specific applications," says Dave Bryant, vocational sales manager-hybrids, Freightliner Trucks. "This includes things such as progressive shifting, road speed limiting, multiple PTO set speeds, ramp (acceleration) rate of PTO speeds and safety interlocks, to name a few.
"In many cases, a customer can also have the engine horsepower and torque rating revised by a software change only, or in combination with hardware changes," he continues. "In the case of engine rating changes, as opposed to operational parameter changes, any re-rate would need to be done with an EPA- and CARB (California Air Resources Board)-certified program to maintain compliance."
"EPA regulations prohibit the re-rating of an engine with an engine rating that is not certified for that engine platform," Mark Ehlers, Navistar's global special tools and diagnostics manager, adds. "The re-rating must also be compatible with all the impacted systems on the truck - fan, clutch, transmission, driveline, etc."
Many engine manufacturers have multiple horsepower and torque ratings to choose from for each of their respective engine families.
"Restrictions apply to ensure the engine has the correct match of components - pistons, cam, turbo, fuel system, etc. - to meet EPA, warranty and reliability guidelines," says Brian Coe, engineering technical steward, Caterpillar Truck Engines. "Additionally, you need to ensure that the rest of the drivetrain is matched to the new engine rating."
All engine builders advise checking with the engine and drivetrain manufacturer before making any changes.
"Cooling and exhaust system performance is critical with today's engines," Coe notes, "so don't forget to get approval from the vehicle OEM as well to make certain these and other chassis components are matched for the new engine rating."
In the case of Mack Trucks, by way of example, "any and all horsepower changes must be approved by Mack Trucks, and if approved, recorded to reflect the new horsepower data files, says David McKenna, the manufacturer's director of powertrain sales and marketing. "When a horsepower change request is received, we first make sure that the rest of the powertrain and cooling system can handle the new data file.
"This is one of the reasons that I always counsel buyers of lower horsepower engines to specify clutches, transmissions and cooling systems that will allow maximum horsepower upgrades for the resale market."