Most commercially available tuners are used to reprogram the parameters inside the PCM to make the engine more responsive and often do increase power and torque and maybe, although seldom, in my opinion, improve fuel economy. I attended a plant tour and afterwards this question was brought up to the engineers at the engine plant. They said that yes, the tuners do and can increase torque and power but that they take the engine “out of compliance.”
They said they wish they could do what the tuners are doing and then repeated many times that the changes made take the engine out of compliance.
These programs do not meet the EPA/CARB requirements and are therefore illegal for on- or off-road use.
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A programmer designed to change the ignition timing and other parameters within the engine controller. The stock settings are retrieved and stored in the unit and replaced with one of three optional “tunes”. Most tunes require the use of premium fuel if the higher performance versions are selected. James Halderman photo