Air/Fuel Ratio A term used for Stoichiometric air/fuel ratio.
colloquial term for the indicator lights on the dashboard which are
illuminated when the vehicle is experiencing some problem such as a
lack of oil, overheating, failed brakes, low fuel, etc. The
alternative is to install gauges which indicate the level of fluids
and temperature. A combination of both gauges and lights is ideal.
mixture of air and fuel (usually about 14:1) being fed to the cylinders.
Mixture Adjustment Screw See idle mixture screw
Mixture Screw A tapered screw located on the outside of
which controls the proportion of the fuel-air
mixture. It is now illegal to adjust these if limiter
caps are present. If you turn the screw clockwise, the mixture will
be leaner while turning it the other way results in a richer mixture.
idle restriction tube or idle jet
A gearwheel between a driving and a driven gear in a gear train
which may serve to reverse the original direction of rotation of the
A free-turning pulley or wheel which serves to maintain tension in a
belt drive. Also see reverse idler gear
a parallel relay-type steering linkage, it is one of the connecting
levers. The steering gearbox is attached to a pitman arm which
converts rotary motion to lateral motion. The pitman arm connects to
a transverse centerlink which connects to the idler arm attached to
the frame side rail on the opposite side of the vehicle. The ends of
the centerlink connect to two adjustable tie rods that transmit the
lateral movement of the centerlink to the steering arms at each
Gear A gear that is placed between two other gears to
reverse the direction of rotation of the output gear. Also see
reverse idler gear
The pulley in a rear derailleur that stays farthest from the
freewheelcogs and functions to keep tension on the chain of a bicycle.
A small pulley located about half way from the front to back of a
long chain such as found on a tandem bicycle.
A spring-loaded pulley designed to maintain the tension of the
timing belt or a cam chain.
fast idle screw
fast idle solenoid
is the speed of the engine with the following conditions: The transmission
is in neutral (or park in automatic
transmissions), the engine
is fully warmed up, the choke
butterfly is fully open, and there is no extra
accessories in operation (i.e., air conditioner, radio, lights).
called "idling speed"
electronically-controlled air bypass around the throttle. Also
called idle-speed stabilizer or a constant idle system
alteration of the engine idle speed.
maintains the idle speed of the engine at a minimum level. There are
currently two types of computer controlled idle speed control: DC
motor ISC and air bypass ISC
Control Motor (ISC)
and ECM controlled motor that extends or retracts a plunger that
contacts the throttle level, which regulates the position of the
throttle valve to compensate for an additional load, such as the air
conditioner, power steering pump, etc. On the engine. Although it
regulates idle speed, it is not used to adjust the curb idle speed.
ISC motors are commonly used on carbureted and throttle body injected
Speed Screw A
screw located at the bottom of the carburetor
on the outside which keeps the throttle
from closing completely when the vehicle is idling and thus controls
the idle speed.
This is adjusted as part of a basic
device which ensures steady engine rpm at idle speed. An
electronically-controlled air bypass around the throttle. Also called
idle speed actuator or a constant idle system
small cylinder located on the outside of the carburetor on some
cars. It prevents the vehicle from continuing to idle after the
ignition switch has been shut off (i.e., dieseling). The position of
the striker rod in the cylinder can be adjusted in a tune-up to the
solenoid-operated valve which cuts off fuel in the idle system of a
carburetor and so stops the engine from running-on when the ignition
is switched off
the throttle valve is closed to such an extent that the airflow
underneath the plunger no longer forms a sufficient vacuum; the fuel
is then supplied via an auxiliary system, the idle system, which
consists of the idle jet, the idle air jet, and the mixture control screw
used on CFI vehicle to inform the EEC if the throttle is in contact
with the DC motor
action of an engine as it turns over at low speed with minimum throttle.
The firing of a spark plug to ignite the air/fuel mixture in the
Box A product that will increase the voltage to a
vehicle's coil, which in turn provides the engine with increased
helps produce a more complete burn of the air and fuel mixture, for
both more power and better fuel economy. Many ignition boxes also
provide multiple sparks, instead of firing just once per cycle, which
also is designed to create a more complete burn. Additional benefits
of an ignition box include quicker throttle response, smoother idling
and starting, and reduced emissions.
Circuit An ignition circuit is made up of two sub-circuits: the
primary, which carries low voltage; and the secondary, which carries
high voltage. The primary circuit is controlled by the ignition key.
It releases 12 volts of electricity from the battery or alternator
through the coil to a set of breaker points in the lower part of the
distributor, or to the relay in electronic ignition applications.
When the points or relay are closed, current flows through the
chassis back to the battery, completing the circuit. When the points
or relay are open, the flow stops, causing a high-voltage surge to
pass from the coil through a rotor in the top of the distributor to
the spark plugs. Once the car has started, the voltage regulator
protects the battery from being overcharged by the alternator. part
of the low -voltage current is absorbed by the condenser when the
points are open.
Coil A pulse transformer which is a part of the ignition
system. It receives a small amount of electrical voltage from the
battery and steps up the low "primary" voltage and
amplifies it into a big jolt of voltage of about 20,000 volts, and
sends it to the spark plugs via the distributor. It is made of two
windings and a core of iron. The primary coil has about 200 turns of
relatively heavy wire. The secondary windings may have as much as
22,000 windings of fine wire. As electricity travels through the
primary winding, it produces a magnetic field in the coil. When the
points open, the magnetic field collapses and the movement of the
magnetic field induces current in the secondary windings of the coil.
The voltage is stepped up in proportion to the ratio of secondary to
primary turns and the distributor directs this high voltage to the
spark plug. Also called just "coil."
Switch A five-position switch that is the power distribution
point for most of the vehicle's primary electrical systems. The
spring-loaded START position provides momentary contact and
automatically moves to the RUN position when the key is released. The
other switch detent positions are ACCESSORIES, LOCK, and OFF.
System The various components that provide the spark to ignite
the air and fuel mixture in an engine during the combustion process.
Some late-model engines (and virtually all vintage engines)
use a distributor to tell the coil when to fire. Many late-model
vehicles feature a distributorless ignition system, in which case the
engine management computer tells the coil when to fire. The spark
energy then passes through the spark plug wires to the spark plugs.
people enhance the performance of an ignition system by adding an ignition
box and a high-performance coil, or even swapping to
higher-performance spark plugs.
Temperature The lowest temperature at which a combustible
material will ignite and continue to burn independent of the heat source.
Timing The moment at which the spark plug fires, usually
expressed in the number of crankshaft degrees before the piston
reaches the top of its stroke.
Wire See spark plug wire.
A rotating member of a centrifugal pump which is equipped with vanes
to convert mechanical energy into fluid energy. A rotor or wheel with
blades or vanes used in pumps to drive and circulate fluid. Also see volute.
A fluid coupling or torque converter - the driving member connected
to the crankshaft via drive plate and converter cover which generates
the fluid flow inside the converter. The driving torus in the fluid
coupling or torque converter of an automatic transmission.
A suspension system where the two front wheels are sprung
independently from each other. It has the advantage over a beam axle
suspension because it allows the engine to be positioned further
forward and lower between the wheels. In this way there is more room
for the passengers, the position of the hood is lower, the vehicle
has a lower center of gravity, and the unsprung weight is reduced.
When the front wheels are not independently sprung, there is some
caster wobble and shimmy that make it difficult to hold on to the
are several styles of IFS, including designs that use coil springs
and designs that feature torsion
Rear Suspension Abbreviated IRS. A type of rear suspension
system in which each wheel and tire operate independently of the
other for better traction in tough conditions. This design also
reduces body roll, as well as a vehicle's tendency to squat down in
the rear when accelerating or leaning forward when braking. By
keeping the vehicle's weight better balanced, IRS improves both ride
quality and handling--and safety. Very few vehicles come with IRS (Corvettes
and Jaguars are among those that do), but it is possible to
retrofit IRS to some cars and trucks.
in which each wheel is sprung individually so that any disturbance
on the wheel has no effect on the opposite wheel.
The way an engine takes in air and fuel. A turbocharger or
supercharger can be used to create a forced induction system, which
can take in more air and fuel than a naturally aspirated system.
That force which tends to keep a stationary object from being
moved, and tends to keep a moving object in motion. Some effort is
needed to get the object moving if it is stopped, and to stop an
object if it is moving.
Manifold British term for intake
Valve British term for intake
engine in which all the cylinders (usually
three or more) are arranged in a straight row (either
vertically or slanted). The pistons drive a common crankshaft.
called a "straight engine."
An inline 4 cylinder engine
Input Shaft The
shaft delivering power into a mechanism. The shaft from the clutch
into the transmission
is the transmission input shaft. Also called clutch shaft. Also see
gearbox input shaft and transmission input shaft
connecting tubes between the base of the carburetor and the port
openings to the intake valve or intake ports. The air-fuel mixture
travels from the throttle body into a chamber called the plenum which
feeds individual tubes (called runners) which lead to the individual
intake port. Its purpose is to transfer the air-fuel mixture to each
cylinder. It is usually an aluminium casting or a GRP molding, with
one intake opening and as many outlets as there are cylinders in the engine.
called "inlet pipe."
term is "inlet manifold."
Stroke The first stroke is called the intake stroke. The piston
moves down the cylinder, creating a partial vacuum in the cylinder. A
mixture of air and fuel is then forced through the inlet valve into
the cylinder by atmospheric pressure, now greater than the pressure
in the cylinder. The exhaust valve stays closed during the stroke.
System The various components that deliver air to a late-model
engine. Air generally flows through an air box and air filter, then
through ducting to the throttle body, and on through the intake
manifold to the cylinder head (or heads). Many people install
less restrictive intake system components to improve a vehicle's
performance and often its fuel economy. Another way to enhance
performance is to swap to a cold air intake system.
Valve A valve in a cylinder head that opens to allow air
and fuel into a combustion chamber. Part of a vehicle's valvetrain.
Any engine, either reciprocating or rotary, in which the fuel is
consumed in the interior of the engine rather than outside of the engine.
How The Internal Combustion Engine in Your Vehicle Works