Glossary of Tuner Terms
Acceleration- The rate of change in velocity with
respect to time. According to Newton's second law of motion,
acceleration is equal to the force, divided by mass (A=F/M).
Accelerator pump- Accelerator pumps are found in
cars equipped with carburetors. When you accelerate, the accelerator
pump delivers extra fuel through the accelerator pump circuit to allow
the engine to deliver more power.
Actuator- An electrical mechanism for moving or
controlling something indirectly instead of by hand, such as a door
lock. Output device the PCM controls such as solenoids, relays, fuel
injectors and stepper motors.
AE - Acceleration Enrichment, the enriched
mixture provided when the throttle position sensor signal changes at
AFR - Air Fuel Ratio, the mass ratio of air
to fuel in the combustion chamber. See NB- and WB-EGO sensors, below.
Air filter- This device filters the air that goes
into your engine. Without an air filter, harmful particles would enter
your car's engine and cause internal wear and damage.
Air pump - Many emissions systems include an air
pump, which pumps fresh air into a vehicle's exhaust to help complete
the combustion process and reduce emissions. To get accurate lambda
measurements with the LM-1, air pumps should be temporarily disabled.
Alpha-N - Alpha-n tuning is
often referred to TPS referenced load control, as this method uses
just the data from the throttle position sensor with relation to
engine RPM and correction factors to control fuel delivery.
Ref Load Control 101
for more detailed information.
ASE - After Start Enrichment, the enriched
mixture provided for a number of engine cycles when an ECU detects
that the engine has transitioned from cranking to running.
Carburetor - A mechanism which mixes fuel with air
in the proper proportions to provide a desired power output from a
spark-ignition internal combustion engine.
Carburetor jet - A fitting inside a carburetor
that meters fuel into a metering circuit where it is mixed with air.
Catalyst - A substance that can increase or
decrease the rate of a chemical reaction between substances without
being physically consumed in the process. A catalyst, which reduces
engine emissions, is used in a catalytic converter.
Catalytic converter - An in-line, exhaust system
device, containing a catalyst, which reduces engine exhaust emissions.
Converters are located near the exhaust manifolds or headers for
Closed loop - refers to those times when an EFI
computer is using the feedback on the mixture provided by the oxygen
sensor to effectively control the injected amounts.
Combustion - The process by which the air/fuel
mixture burns within an engine to create power.
Computer (PCM) - Many modern cars have a central
computer called an engine control unit (ECU) or power train control
module (PCM). This controls the car's fuel and ignition systems by
taking information from various sensors to determine how to run the
engine with the most efficiency and power.
Converter (Torque) - A fluid coupling device which
multiplies torque between an engine and automatic
transmission/transaxle. When a vehicle is stopped, a converter allows
enough fluid slippage, so the engine can idle without stalling.
CTS - Coolant Temperature Sensor. Usually
the CTS is an NTC (Negative Temperature Coefficient) thermistor, or a
resistor whose resistance varies with temperature (NTC means the
resistance goes down as the temperature goes up.
DMM (digital multi meter) electronic
current/resistance/potential measuring tool.
Double overhead cam (DOHC) - A DOHC engine has two
camshafts in the cylinder head - one for the exhaust valves, and one
for the intake valves. This allows greater efficiency and greater
Driveline - The system of components that connects
the transmission to the wheels. The driveline consists of axles,
differentials, constant velocity (CV) or universal joints, and a
Driver - A switched electronic device housed in a
computer that controls output state. For example, a driver controls
how long a fuel injector remains open.
Duty Cycle (DC)– A number indicating the amount of
time that some signal is at full power. In the context of an ECU, duty
cycle is used to describe the amount of time that the injectors are
on, and to describe the “hold” part of the peak and hold injector
drivers (see Low Impedance Injectors, below).
Early Fuel Evaporation - Used on
carburetor-equipped engines only, a system where heat is used to help
increase early fuel evaporation of the cold-start air/fuel mixture to
achieve more efficient combustion and lower emissions. GM used an
electric grid system.
EGO Sensor - Exhaust Gas Oxygen sensor,
used to describe the sensor in the exhaust that measures the lean/rich
state of the AFR. Used to control the via a feedback algorithm called
Emissions - Emissions are the byproducts of
combustion. After combustion is complete, water, gases, and carbon are
released through the car's exhaust system as emissions.
Emissions equipment - Emissions equipment is
equipment required by the government to keep a car's exhaust emissions
to a minimum. Emissions equipment includes catalytic converter, air
pump, and oxygen sensor.
Engine - A machine designed to convert thermal
energy into mechanical energy to produce force or motion. Connected to
a drivetrain, an engine's mechanical energy, or torque, moves a
vehicle. An engine can run by using gas, diesel fuel, steam or other
Engine accessory - An engine accessory is a
peripheral piece of equipment that runs directly off of the engine's
power to supply energy or a fluid to another part of the car. Engine
accessories include the alternator, power steering pump, air pump, air
conditioning compressor, as well as many others.
Engine block - The engine block is where the
cylinders and pistons reside. The block is the strongest part of the
engine and withstands tremendous pressures while the engine is
Engine temperature sender - The engine temperature
switch and sending unit measure the temperature of the engine's
coolant. They send this information to the engine temperature warning
light and engine temperature gauge, respectively. Compare to coolant
temperature sensor (CTS) which transmits the coolant temperature to
the computer, and the radiator fan switch which engages the radiator's
Fuel injection - Fuel injection is a system by
which fuel is directly sprayed into the intake manifold or intake port
at high pressure. Fuel injection is often controlled by a computer,
allowing precise monitoring of efficiency and performance by the car's
Fuel injector - A device for delivering metered,
pressurized fuel to the intake system or individual cylinders. An
injector sprays fuel, which helps atomization for a more dense
mixture, when combined with incoming air.
Fuel pump - The fuel pump moves gas from the gas
tank and delivers it to the fuel injection system or carburetor.
Fuel starvation - Fuel starvation occurs when
fuel, for one reason or another, is prevented from reaching the
carburetor or fuel injectors.
Fuel system - The fuel system is the system by
which fuel is stored and delivered to each cylinder. The fuel system
includes the fuel tank, fuel tank level sending unit, the fuel pump,
the fuel filter, and fuel lines. For carbureted cars, the fuel system
also includes the carburetor. For fuel injected cars, the fuel system
also includes injectors, fuel pressure regulator and often a main
G-Force - Unit of measurement used to describe
lateral acceleration generated while the vehicle is driven in a steady
state turn on a skid pad circle. An average sedan generates 0.60 G of
lateral acceleration. Measured in "gravities", one G equals the
earth's gravity at sea level.
Ground - An electrical conductor used as a common
return for completing an electric circuit(s). Car batteries contain a
ground terminal, usually the negative terminal.
Head gasket - The head gasket seals the cylinder
head to the engine block. It is subject to tremendous pressures, and
often fails if and when an engine overheats.
Headers - Constructed from steel tubing, headers
provide a smooth and efficient exhaust flow path from the exhaust port
to the exhaust system. Headers are frequently used in performance
engine applications and are generally less restrictive than the stock
exhaust manifold, resulting in increased power.
High Impedance Injectors - (a.k.a. hi-Z) Fuel
injectors designed to work with a simple switch in a 12 volt circuit,
no special signal conditioning is required to drive them. The
resistance of a high impedance injector is about 10-15 ohms.
IAC – Idle Air Control. Typically a
IAT sensor - Intake Air Temperature sensor,
same as MAT, see below.
Idle circuit - This is a special kind of circuit
found in a carburetor that only operates when the engine is at an
Ignition - Complete system used to step up battery
voltage to a higher voltage and deliver it to the spark plug to
complete the combustion process. When the key is turned on, the
ignition system is energized.
Ignition Advance/Retard - The advancing or
retarding (in crank degrees) of ignition spark relative to the piston
location in the cylinder. In performance applications, the goal is to
set ignition timing such that peak cylinder pressure occurs at 16-18
degrees after top dead center (TDC).
Ignition module - Part of the ignition system
which instructs the ignition coil to send current to the distributor.
Ignition system - The ignition system contains the
components that supply spark to the vehicle's spark plugs. These
include the battery, the ignition coil, the distributor (including the
cap and rotor), the spark plug wires, the ignition module, and the
spark plugs themselves. Older cars also have ignition points and an
Knock (Engine) - The sharp, metallic sound
produced when two pressure, or flame fronts collide in the combustion
chamber. This could be the result of incorrect ignition timing,
incorrect air/fuel mixtures, or the wrong grade (octane rating) of
gas. Also known as Detonation.
kPa (kiloPascals) - the measurement of air
pressure used in some ECU computations. Average pressure at sea level
is 101.3 kPa.
Lambda – the ratio between actual air/fuel ratio
and stoichiometric ratio. Lambda of less than 1 is rich, and greater
than 1 is lean.
Load Control - Load is
essentially a measurement of airflow since, as discussed in our
Volumetric Efficiency article an engine is essentially a large air
pump. Since airflow determines load and is directly correlated to
volumetric efficiency, and it’s operating parameters, including fuel
and ignition requirements, it is critical that we have an
understanding and a methodology for calculating, measuring and or
programming the load of their particular engine configuration. Once
airflow is known, fueling and other operating parameter simply become
trivial scientific calculations.
Low Impedance Injectors - (a.k.a low-Z) Fuel
injectors that are designed to run at a much lower current than would
be supplied by a direct 12 volt connection. They require a special
signal that is initially at full current (4-6 amps, a.k.a. “peak
current”) for about 1.0-1.5 ms, but then drops down to about 1 amp
(“hold current”) for the rest of the opening pulse. The resistance of
a low-impedance injector is typically 1-3 ohms.
MAF Sensor - Mass Air Flow
sensor. Sensor, normally mounted directly in the air intake system
to extract a measurement of the actual air flow (in units of
Load Control 101 for how MAF is used in the calculation of
MAP sensor - Manifold Absolute Pressure sensor.
Measure the absolute pressure in the intake manifold (related to the
engine vacuum), to determine the load on the engine and the consequent
MAT Sensor - Manifold Air Temperature sensor,
the same as IAT. The MAT circuit is identical to the CTS circuit, see
NB-EGO Sensor - Narrow Band EGO sensor,
gives a switch at the stoichiometric ratio (the chemically correct
mixture of air and fuel), but unreliable for AFR other than
OEM (original equipment manufacturer) -
refers to parts produced for initial assembly of a new vehicle.
Open Loop - refers to those times when ECU ignores
the feedback from the oxygen sensor.
P&H Injectors - Peak and hold injectors;
see Low Impedance injectors.
Pulse Width Modulation (PWM) - A signal
with a fixed pulse width (frequency), which is turned on for part of
the pulse. The percent of time that the signal is on is called its
duty cycle. PWM is used to control voltage (and consequently current)
to fuel injectors.
Required Fuel – For some ECUs and EFI systems, the
injector pulse width, in milliseconds, required to supply the fuel for
a single injection event at stoichiometric combustion, 100% volumetric
efficiency and standard temperature.
Speed Density -
Speed-density is one
of the most common methods of load control and airflow calculations.
This method uses an equation relating the manifold absolute pressure
(MAP) and the intake air temperature with the known
characteristics of the engine to calculate airflow, and thus makes it
possible to calculate fueling requirements.
Stoichiometric Ratio- The ratio at which all
available fuel is combined with oxygen during the combustion process.
This theoretically ideal ratio produces minimum emissions, however
maximum power is achieved at an AFR 10-15% richer than stoichiometric,
while maximum efficiency is achieved at an AFR 3-5% leaner than
stoichiometric (depending on many engine variables).
TPS - Throttle Position Sensor, a voltage
divider that provides information about throttle opening, from which
it computes rate of throttle opening for acceleration enrichment.
VE - Volumetric Efficiency. The actual
amount of air being pumped by the engine as compared to its
theoretical maximum. A 200 cubic inch motor will theoretically move
200 cubic inches of air in one cycle at 100% efficiency. If the engine
is actually running at 75% VE, then it will move 150 cubic inches of
air on each cycle.
Ref: Volumetric Efficiency 101
WB-EGO Sensor - Wide Band EGO sensor, can
be used to derive real AFR data with mixtures from 10:1 to 20:1, i.e.
anything you are likely to be interested in.
WOT - Wide open throttle.
WUE - Warm Up Enrichment, the enriched
mixture applied when the coolant temperature is low.