An electronic control unit, commonly known as a chip, is a generic term in automotive electronics for a microprocessor that controls electrical systems. Modern trucks may have up to 80 chips, and this number continues to increase steadily.
The software that operates these chips is also becoming more complex, making chip management a growing challenge for truck manufacturers. Reprogramming chips is a common aftermarket practice and is usually done to improve a truck’s fuel economy or performance.
The term “chip” often refers specifically to an engine control unit (ECU), which controls engine performance. An ECU reads measurements from numerous sensors in the engine bay and uses multi-dimensional performance maps, or lookup tables, to interpret this data. The ECU then controls a series of actuators to achieve the behavior indicated by the lookup tables. An ECU therefore adjusts engine behavior dynamically, as opposed to the static behavior created by traditional mechanical and pneumatic methods.
Many modern ECUs don’t have a fixed behavior. A qualified technician can program these chips to exhibit a specific behavior, usually for the purpose of tuning a particular engine.
This capability is especially important when you make aftermarket modifications to your truck that affect engine performance, since the ECU’s default settings will typically fail to provide optimum behavior with the new configuration. Modifications that are most likely to benefit from reprogramming the ECU include adding a turbocharger or intercooler, changing the exhaust system and converting the engine to use an alternative fuel.
An engine technician can adjust many of the parameters that affect engine performance.
Assume for this example that the technician wants change the amount of fuel that’s injected into the cylinders. The ideal quantity depends on parameters such as the position of the accelerator pedal, engine RPM and manifold air pressure.
The technician will typically connect the truck to a dynamometer to provide a controlled testing environment. This practice is especially common in racing and other high-performance applications, which require a precise calibration of the engine. The technician then connects a laptop loaded with the appropriate software to the ECU via a serial or USB cable.
The ECU software displays a spreadsheet that shows RPM values and their corresponding pedal positions. This spreadsheet is commonly called the fuel map or fuel table. Each cell in the fuel map shows the amount of fuel to inject into the cylinder at each pedal position. The technician then gathers data for the fuel map by running the engine at various RPMs and measuring the exhaust fumes with a device known as a wide-band lambda probe.
This procedure tells the technician if the engine is receiving the optimum air/fuel mixture for each position of the accelerator pedal. The technician can then modify the values in the fuel map to adjust the air/fuel mixture as desired.
Fuel efficiency is typically an important concern for truck drivers, since a slight difference in efficiency can mean a large difference in cost over time. The factory settings for the ECU may provide good fuel economy in general, but they can’t account for specific conditions.
For example, actual fuel economy is highly dependent upon parameters such as individual driving behavior, geographic location and maintenance practices. Reprogramming an ECU can therefore provide a significant improvement in fuel economy for a particular truck.
An ECU can also be tuned to improve performance, although this often requires sacrificing fuel economy. ECU parameters that are particularly important for engine performance include fuel delivery and fuel/air mixture. The factory settings for these parameters are typically tuned more for fuel economy than performance on trucks.
Horsepower and torque are often vital considerations for truck drivers, especially if they must tow heavy loads over long distances. Increasing torque also reduces the stress on the transmission since less energy is expended in maintaining a given speed within a gear.
Tuning the ECU often results in an improvement, regardless of the specific changes required. This general rule is especially true for non-stock configurations.