The terms you will meet when ordering a tune or reading a data log, explained without the jargon.
- Boost
- Intake manifold pressure above atmospheric pressure, produced by the turbocharger and normally shown in psi.
- BSFC (brake specific fuel consumption)
- Fuel mass burned per unit of power produced, for example pounds of fuel per horsepower-hour. It is a useful sanity check: fuel flow equals power multiplied by BSFC, so a claimed power figure that needs more or less fuel than the injectors and pump can supply is wrong somewhere.
- Calibration
- The collection of tables, maps and constants inside a controller that tells it how to behave. A “tune” is the everyday name for a modified calibration.
- Checksum
- A value calculated from the contents of a controller file so the controller can verify the file is intact. After a file is edited the checksum has to be corrected, or the controller may refuse the file.
- Data log
- A recording of controller values (engine speed, boost, rail pressure, exhaust temperature and more) captured while the engine runs. Logs are the best way to verify that a calibration is doing what it should.
- Derate
- A power reduction the controller applies when it detects a fault or a protection condition such as high temperature.
- DOC, DPF, SCR and DEF
- Parts of a diesel exhaust aftertreatment system. The diesel oxidation catalyst (DOC) treats hydrocarbons and carbon monoxide, the diesel particulate filter (DPF) traps soot, and selective catalytic reduction (SCR) uses diesel exhaust fluid (DEF, a urea solution) to reduce oxides of nitrogen.
- ECM / ECU
- The engine control module (also called the engine control unit): the computer that controls fueling, injection timing, boost and many other engine functions.
- EFI Live (EFILive)
- A software and hardware suite widely used to read, edit and flash GM controllers, including Duramax, and some other platforms.
- EGR
- Exhaust gas recirculation: routing a portion of exhaust gas back into the intake to lower combustion temperature and reduce oxides of nitrogen.
- EGT (exhaust gas temperature)
- The temperature of the exhaust gas, measured before the turbine (pre-turbo) or after it (post-turbo). Sustained high exhaust temperature can damage pistons, the turbocharger and exhaust components, so safe limits depend on the engine and its hardware.
- Injection quantity
- The amount of fuel delivered per injection event or per stroke, often expressed in cubic millimeters per stroke.
- Injection timing
- When injection starts relative to the piston position, usually given in degrees of crankshaft rotation before top dead center. Advancing timing generally raises cylinder pressure and lowers exhaust temperature but can increase combustion noise and oxides of nitrogen; retarding does roughly the opposite.
- Lambda / air-fuel ratio
- The amount of air available compared with the amount needed to burn the fuel completely. Diesels normally run lean (lambda above 1); pushing lambda too low at high load causes smoke and high exhaust temperature.
- Pilot, main and post injection
- A single combustion event can be split into several injections. A small pilot injection before the main event softens combustion, the main injection makes most of the torque, and post injections occur after it, for example to help aftertreatment.
- Pulse width / injector duration
- How long an injector is energized. Together with rail pressure and the injector’s flow characteristics, it determines how much fuel is delivered.
- Rail pressure
- The pressure of the fuel stored in the common rail that feeds the injectors. Higher pressure atomizes fuel more finely, but it is limited by what the high-pressure pump and injectors are built to handle.
- Smoke limit
- The maximum fuel quantity the controller allows for a given amount of airflow before the engine would produce excessive smoke.
- Stock read
- An unmodified copy of a controller’s software, read before any changes are made. It is the starting point for custom work and your way back to original.
- TCM
- The transmission control module, which manages shift points, line pressure and torque converter lockup in an automatic transmission. On some vehicles this function sits inside another controller.
- Torque model
- Many modern diesel controllers are torque-based: the pedal is turned into a torque request, that request passes through several limiters (for example smoke, temperature, boost and driveline limits), and the final torque is converted into fuel quantity.
- VGT (variable-geometry turbocharger)
- A turbocharger whose vane position is adjusted by the controller to regulate how much exhaust energy reaches the turbine, giving boost control across the rev range.
- Wastegate
- A valve that lets exhaust bypass the turbine to limit boost.
- WinOLS
- Software used to view and edit the binary data of controller files, find the maps inside them and modify them.
Want to see these in practice? Read our articles or start a custom tune.