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
various rates.
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, air pumps should be temporarily
disabled.
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
maximum efficiency.
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
power.
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
driveshaft.
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 “closed
loop”.
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 fuel sources.
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
operating.
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 cooling fan.
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 computer.
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 computer.
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 “stepper
motor”.
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
idle.
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
ignition condenser.
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.
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.
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 fueling requirements.
MAT Sensor - Manifold Air Temperature sensor, the same
as IAT. The MAT circuit is identical to the CTS circuit, see CTS,
above.
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
stoichiometric.
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.
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.
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