Diesel Tuning

Reprogramming diesel engines for better fuel efficiency

OEMs work with a number of electronic diagnostic tool manufactures to develop products that support varying levels of diagnostic and parameter programming, Bryant says. These tools should not be used to change engine calibrations related to emission compliance.

For example, he says that changes to fuel injection rates or timing that have not been certified to meet EPA and CARB compliance would not be approved by the engine manufacturer. However, adjusting the progressive shift rate or top speed to meet the needs of a specific fleet would be fine.

"Engine manufacturers generally do not condone tuning products," acknowledges Mike Litsch with DiabloSport, a company that designs and manufactures gasoline and diesel tuning systems. "They are often of the belief that they cause damage to the engine. Unfortunately, there are many products available, some better than others, and a few poor products have left a bad taste in the mouth of many of the manufacturers."

DiabloSport's diesel performance tuning products "can actually make the trucks run much better than OEM with no change in engine emissions," he says. The electronic products increase power and fuel mileage through optimizing fuel burn and boost output. The products function by communicating with the factory PCM (powertrain control) module through the OBDII communications port.

"We do quite a bit of work to get to a point where we can read and write the PCM, then we edit the files, test the tunes and develop a product safe for the retailer and ready to use," says Litsch.

Bully Dog Technologies is another vehicle performance company with products for diesel engines. Its Bully Dog Big Rig Power Pup programmers/tuners "give 6 to 12 percent mileage gains backed by a money back guarantee," says Greg Cox, national industrial sales manager, and notes that fuel economy savings have been documented by SAE J1321 Joint TMC/SAE Fuel Consumption Test Procedure Type II and field testing.

The devices download "safe and simple" engine software upgrades and reprogram the ECM with engine tuning modifica¬tions, he explains. These tunes are designed to improve the engine's efficiency, resulting in improved fuel economy and increased horsepower and torque.

Bully Dog engineers have worked to ensure that the programs do not exceed safety parameters, says Cox "We suggest using caution if you have already tuned the truck to the highest horsepower level or have the highest OEM horsepower tune for your configuration. Transmissions, clutches and drivelines already set to their highest horsepower level should not be exceeded."

As for whether diesel tuning systems affect the engine's warranty, DiabloSport's Litsch says: "Before we flash any vehicle, we read the stock tune out of the PCM, saving it so it can be restored back to the original setting at any time. While there is no trace of the tune actually having been there, it is always a good idea to restore the stock tune to the vehicle before going for any type of warranty repairs."

Bully Dog Technologies' product literature states: "The Bully Dog programs that are loaded onto the engines do not interfere with the current OEM tools. Unless you tell them that the program is loaded onto the tractor they will not know that it is there."

In January, Bully Dog joined the EPA's SmartWay Community program, which is under the umbrella of The SmartWay Transportation Partnership. It is a voluntary affiliation between various freight industry sectors and the EPA that establishes incentives for fuel efficiency improvements and greenhouse gas emissions reductions.


With the sophistication of engine electronics and service tools, the day of the "diesel tuner" (a mechanic that can "tweak" an engine) is long gone, the engine builders say. "With earlier versions of engine data files, they were very simple and could easily be 'adjusted' to develop more power and speed," says Mack Trucks' McKenna. "Today the data files are huge and equally complex and are very difficult to modify, tweak, adjust or call it what it is - tampering."

"There is tremendous flexibility to modify the parameters on today's electronic engines to meet application needs," Bryant of Freightliner Trucks adds. "However, tweaking an engine for higher horsepower or torque apart from using an OEM-certified calibration is not recommended."

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