What ACT Means ?

Air Charge Temperature (also known as IAT, Intake Air Temperature) Sensor used to determine the temperature of air entering the engine, usually variable resistance thermistor.

What AE Means ?

Acceleration Enrichment. Additional fuel added to the normal delivery to account for the rapid onset of airflow and evaporation of the wall film during tip-in maneuvers.

What AFR Means ?

Air to Fuel Ratio. Comparison in units Of mass between airflow and fuel flow. Since pounds are divided by pounds, AFR is a ratio without units.

What Aircharge Means ?

Also known as Air- mass. The amount Of air present inside the cylinder on a single intake event, measured in units of mass.

What Alpha-N Means ?

Type Of speed density control logic based upon two primary inputs, throttle angle (alpha) and engine speed (N). This control logic is especially well suited to applications without a stable MAP signal, such as “stack” injection systems.

What CO Means ?

Carbon Monoxide. An emissions component that is the result Of combustion with a rich condition.

What Coefficient Means ?

Multiplier, as used to modify another table or value for an additional condition.

What Correction Factor Means ?

1) Multiplier applied to dynamometer data (horse- power and torque) to simulate actual output at reference conditions. 2) Multiplier applied to calibration data to bring calculated values in line with actual physical values.

What Cycle Time Means ?

Duration between intake valve opening events. In a four-stroke engine, cycle time represents two complete engine revolutions or 720 degrees of rotation.

What DE Means ?

Deceleration Enleanment. Rem- oval of fuel mass in the normal delivery to account for the rapid decrease Of airflow and buildup Of the wall film during tip-out maneuvers.

What Deadtime Means ?

Delay between initial energization of the injector coil and the time at which it reaches an open position. Opening delay.

What DFCO Means ?

Deceleration Fuel Cut Off. Complete removal Of fuel injection events during closed throttle at elevated engine speeds resulting in a negative net engine torque (engine braking).

What DTC Means ?

Diagnostic Test Code. Numeric or alpha-numeric code used to indicate a specific fault condition. These often vary by manufacturer.

What Dwell Means ?

Duration Of time that power is applied to an ignition coil. Increases in dwell increase available spark energy as well as heat applied to the coil. A spark event occurs at the end of dwell when primary volt- age is removed.

What ECM Means ?

Engine Control Module. Common acronym for an electronic engine control box or system.

What ECT Means ?

Engine Coolant Temperature. Sensor used to determine the temper- ature of the water or other cooling fluid Of an engine, usually variable resistor thermistor.

What ECU Means ?

Engine Control Unit. Com- mon acronym for an electronic engine control box or system.

What EEC Means ?

Electronic Engine Controller. Common acronym for an electronic engine control box Or system.

What EGR Means ?

Exhaust Gas Recirculation. 1 -n) Amount of previously com- busted gases either retained in the cylinder or reintroduced to the intake charge. 2-v) The motion by which Spent gases are retained Or reintroduced into the cylinder. Increases in EGR reduce bulk burn temperature and slow combustion speed.

What EMS Means ?

Engine Management System. Common acronym for an electronic engine control box or system.

What ETC Means ?

Electronic Throttle Control. A motor assembly attached to the throttle blade shaft that is able to replace the traditional cable connection. This system requires the addition of a pedal position sensor and ECU control logic that provides the necessary output to move the motor on the throttle shaft.

What HC Means ?

Hydrocarbons. An emissions component that usually represents unburned fuel, typically the result of combustion with either an excessively rich Or lean condition.

What Horsepower (hp) Means ?

Unit of measure for engine output representing avail- able torque per unit of time. 1 hp is equal to 550 ft-lb/sec, 33,000 ft- lb/min, or 0.7457 kW.

What Joule (J) Means ?

Metric unit of energy equal to 1 Pascal times 1 cubic meter. 1J = 1 Pa-m3•

What Kelvin (K) Means ?

Unit Of temperature measure with identical increments to Celsius, but where 0K is equal to absolute zero. 0 degrees C (32 degrees F) is equal to 273.15K.

What Lambda (X) Means ?

Excess air ratio (percent enleanment), an engineering unit of measure used to describe air to fuel ratio divided by the stoichiometric mixture. A value of lambda-I .00 is equal to 14.68:1 for gasoline.

What LBT Means ?

Lean Best Torque. Air/fuel ratio that correlates to the minimum fuel enrichment required to achieve near maximum engine torque output.

What Load Means ?

Numeric representation Of cylinder mass charge filling usually expressed as a percent. It represents the current mass of intake charge divided by the theoretical maximum airmass that would occupy the cylin- der volume at standard temperature and pressure conditions.

What MAF Means ?

Mass Air Flow. 1) Total amount of air entering an engine per unit time, measured in weight (mass). 2) Sensor that measures number of molecules of air entering the engine and returns either a voltage or frequency output proportional to the flow rate.

What MBT Means ?

Maximum Brake Torque. Ignition angle that provides the greatest engine torque output for a given speed, load, and ambient conditions.

What Newton (N) Means ?

Metric unit of force equal to the amount necessary to give one kilogram an acceleration of one meter per second squared. IN = 1 kg-m/s2•

What Nox Means ?

Oxides of Nitrogen. An emissions component that forms under high combustion temperatures when the nitrogen in air is broken down and allowed to mix with oxygen ions.

What OEM Means ?

Original Equipment Manufacturer. A company whose prime business is the design, testing, and production of automobiles such as GM, Ford, Chrysler, BMW, Honda, and Toyota.

What Opening Delay Means ?

Length Of time between energization of a solenoid (e.g., fuel injector) and movement of the pintle. This is primarily a function of the inductance of the coil and resistive force applied to the pintle.

What IAC Means ?

Idle Air Control. A variable output control that diverts a small amount Of airflow around the throttle blade to precisely control airflow into the engine during closed throttle and idle conditions. The IAC acts as a “slow path” control for idle speed.

What IAT Means ?

Intake Air Temperature, see ACT.

What Injector Offset Means ? — Additional time added to a target pulsewidth to compensate for both opening and closing delays.

What MAP Means ?

Manifold Absolute Pressure. 1) Pressure as measured between the throttle body and intake valve. Absolute pressure indicates that the reference is absolute zero (O bar), such that atmospheric pressure is shown as 1 bar (14.5 psi). 2) Sensor that measures intake pressure relative to zero. A 2 bar MAP sensor has the ability to measure up to 1 bar (14.5psi) gauge pressure Or “boost.”

What PCM Means ?

Powertrain Control Module. Engine controller that also includes transmission control capability.

What Phi (cp) Means ?

Enrichment Ratio (percent enrichment). An engineering unit of measure used to describe the stoichio- metric ratio divided by the current air to fuel ratio. A value Of is equal to 14.68:1 for gasoline.

What Pulsewidth Means ?

Time that a fuel injector is energized and the driver circuit (transistor) is subject to cur- rent flow. It is not possible for injector pulsewidth to exceed available cycle time.

What PWM Means ?

Pulse Width Modulation. A method of electronic output control that switches a device on and off at known frequency. Percent of “on” time is varied, resulting in a change of average output value. This allows for variable control of an otherwise binary device or system.

What R Means ?

Universal Gas Constant. For air, this is equal to 287.05 J/Kg-K or 8.3145 J/m01-K.

What RBT Means ?

Rich Best Torque. Air/fuel ratio that correlates to the maxi- mum amount of fuel enrichment that still provides near peak engine torque output.

What Standalone Means ?

A control unit that does not require interaction with any other vehicle modules.

What Stoichiometry (Stoich) Means ?

A condition in which the chemical components of a reaction are balanced, often stated as a ratio. If a complete reaction occurs, this condition will result in no leftover components. For combustion of gasoline in air, this is a ratio of approximately 14.68 parts air to 1 part fuel.

What STP Means ?

Standard Temperature and Pressure. Reference defining “nor- mal” environmental conditions. 15.5 degrees C (60 degrees F) and 101.3 kPa (29.92″ Hg) STP conditions typically result in horsepower numbers about 4% higher than SAE conditions.

What Tau (T) Means ?

Time constant for evaporation of the fuel wall film.

What TDC Means ?

Top Dead Center. The point at which a piston has reached its maxi- mum vertical movement and mini- mum clearance volume to the cylinder head as the connecting rod reaches full extension on the crank- shaft’s movement.

What Transient Fueling Means ?

Additional fuel used to offset the wall film effect during acceleration. Also refers to fuel removed during deceleration to avoid excess enrichment.

What UEGO Means ?

Universal Exhaust Gas oxygen (sensor). A wideband sensor that has an extended accurate range of air/fuel ratios. Output from the sensor itself is milliamps of pump cell current, which must be converted to a useful display or analog voltage by an external controller.

What Volumetric Efficiency (VE) Means ?

Numeric representation of cylinder volume charge filling, usually expressed as a percent. It represents the equivalent volume that the intake charge would occupy if it were at STP conditions divided by the actual cylinder volume.

What TDC Means ?

Top Dead Center. The point at which a piston has reached its maxi- mum vertical movement and mini- mum clearance volume to the cylinder head as the connecting rod reaches full extension on the crank- shaft’s movement.

What Thermistor Means ?

A resistor whose impedance changes with respect to temperature; often used for ECT and ACT sensor applications.

What Tip-in Means ?

Positive change in throttle angle resulting from an increase in driver demand at the gas pedal.

What Torque Means ?

Twisting force measured in units of mass per unit length. Most engines are measured in units of foot- pounds (ft-lbs) or Newton-meters (Nm). At a given torque value, the available force (pounds) increases as the acting radius (feet) decreases.

What TPS Means ?

Throttle Position Sensor. A rotary resistor installed on the throttle shaft that changes impedance with respect to angle.

What Wall Film Means ?

Volume of fuel that clings to the inside of an intake port or runner. Its size and location are the result of the injector spray pattern and targeting. Fuel that evaporates from the wall film joins fuel from the injector spray to form the complete fuel charge entering the cylinder. Increases in port temperature or air- flow will tend to decrease its size.

What Wideband Means ?

Generic term for a wide-range UEGO sensor. This is often used to describe both the sensor itself and the external controller or display unit. Most wideband oxygen sensors have an approximate accurate range of lambda=0.7-1.1 (1():1 up to 16:1 air/fuel ratio with gasoline)

What WOT Means ?

Wide open Throttle. Condition where the throttle blade is completely open, allowing the engine to move as much air through it as possible.

What SAE Means ?

Society of Automotive Engineers. I) Organization responsible for developing standards for testing and measurement of a wide range of automotive components, including engines. 2) Reference used to define “normal” environmental conditions for engine testing, 25 degrees C (77 degrees F), 99 kPa (29.23″ Hg), 0% humidity, and mechanical efficiency.

What Speed Density Means ?

Control logic for an engine that estimates the current aircharge based on engine speed and pressure present within the intake manifold.

What Steady State Means ?

A condition in which all characteristics of engine function are not changing significantly. Most importantly, speed, manifold pressure, throttle angle, airflow, air/fuel ratio, ignition angle, air and coolant temperature.