Reader asks about high-performance tuners


Jeff T. writes via email: “Regarding performance chips: Do they actually improve mpg and performance? Do they void the warranty? For $50 to $300, are they worth it? A plug-in module for less than $100 that claims 10% to 15% gain in horsepower seems attractive.”


There are many aftermarket programmers or “tuners” available in the marketplace today. Some like the lower cost units, simply plug into the engine coolant temperature (ECT) sensor to change the signal back to the engine controller to indicate that engine is colder than it is. When the engine is cold, the powertrain control module (PCM) commands a richer air-fuel mixture. This richer mixture usually results in an increase in power at the expense of reduced fuel economy.

Another “trick” used by some lower cost devices is to “fool” the electronic throttle control (ETC) system by changing the curve of the accelerator pedal position (APP) sensor to make the engine more sensitive. This makes the engine appear to have more power and greater responsiveness.

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

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