Below is a list of terms and definitions you will encounter when learning about tuning and software.
Adaptation – a feature on modern BMWs that enables the DME to make realtime changes in fuel so it can meet pre-determined targets for efficiency and power.
AFR – Air/Fuel Ratio, is the expression of how much fuel is mixed with air in the exhaust stream. The ideal ratio for fuel and oxygen for burning is 14.7:1. However, BMW engines rarely aim for this target. These engines make more power at a richer AFR (12.5-13.5 is typical on naturally aspirated engines). But while cruising or low load conditions, the AFR will run lean (15.0 or higher) for better fuel economy.
CARB – California Air Resources Board, a semi-autonomous regulatory agency that establishes air quality standards for California. These emissions laws affect all cars registered in the state and sometimes supersede federal regulations.
Chip – a computer chip (EPROM) installed in the DME that contains the software. 1982-1995 BMWs have a replaceable chip in the DME. 1996 and later computers have a flash memory chip.
Closed loop – a DME operating strategy where it makes realtime changes in engine operation based on data from the O2 sensor. Closed loop is in effect from idle to approximately 70% throttle opening.
DME – Digital Motor Electronics. This is the computer that manages engine operation and performance. Also known as an ECU.
ECU – Electronic Control Unit or Engine Control Unit. This is the computer that manages engine operation and performance. Also known as a DME.
EPROM or EEPROM – Erasable Programmable Read-Only Memory or Electrically Erasable Programmable Read-Only Memory. Otherwise known as a chip.
EWS – a theft-protection system on 1993-later models that syncs various systems in the car so that the car only starts with the key. In other words, it cannot be hot-wired. Since 1995 the DME has been an integrated part of the EWS system.
Flash – a way of overwriting existing data in the software without replacing a physical chip. BMW computers have used flash memory chips since OBD-II standards in 1996.
Flash Counter – an internal limit on how many times a DME can be flashed with a new version
Jim Conforti – computer engineer and BMW tuner, famous for his OBD-I performance chips and OBD-II Shark Injector
Lambda – another but lesser-known method for measuring AFR. The AFR of 14.7 is equal to a Lambda of 1.0. BMW Lambda should be around 0.92-.95 for power output and 1.1-1.3 for cruise.
Lean – using less fuel (the opposite of rich)
OBD – On Board Diagnostics, the self-contained diagnostic and communication system in a BMW. The DME is at the heart of this system. There is a diagnostic port located in the engine bay (1977-2000) or in the dashboard (1996-later).
OBD-I – an emissions and communications standard recommended by the US federal government. For BMWs, OBD-I applies to 1986-1995 models. Nearly all OBD-I vehicles have a single oxygen sensor ahead of the catalytic converter.
OBD-II – an emissions and communications standard required by the US federal government. For all cars, OBD-II applies to 1996+ models. Nearly all OBD-II vehicles have multiple oxygen sensors to evaluate the performance of the catalytic converter and the rest of the emissions system. There is one or more O2 sensors ahead of the catalytic converter and one or more after the cat. Modifying or removing OBD-II software that affects emissions is against federal, and possibly state, law.
Open loop – a DME operating strategy where it ignores data from the O2 sensor and reverts to preset tables and maps for engine operation. Open loop is in effect at full throttle (> 70% throttle opening).
Oxygen sensor – a sensor that measures the oxygen content in the exhaust and compares it to outside air. The DME uses this data to evaluate the efficiency of the engine. Most stock O2 sensors measure in a ‘narrow band’ (see Wideband below) of 12.0-16.0 because that’s all the DME is equipped to record. The oxygen sensor was invented by Bosch engineers in the early 1970s. Also known as a Lambda sensor.
Piggyback – a module that intercepts sensor data, modifies it, and sends the new data to the DME. By altering the signals from various sensors you can trick the DME into using alternate maps to make more power. Piggyback units are used when the factory DME cannot be tuned or the tuner does not fully understand how to tune it.
Rich – using more fuel (the opposite of lean)
Shark Injector – a DIY software flashing tool, developed by Jim Conforti
Wideband O2 Sensor – a sensor that measures the oxygen content in the exhaust and compares it to outside air. Wideband measures AFR in a broader range than a stock O2 sensor – typically 10.5-straight air.