MICROPROCESSORThe small, on-board solid-
state electronic device that acts as the central
processing unit. Sensors provide input information
which the microprocessor uses to determine the
desired response (in any) as an output signal.
MUFFLERIn the exhaust system, a device through
which the exhaust gases must pass and which
reduces the exhaust noise.
MULTIPLE-POINT INJECTIONA gasoline fuel
injection system in which only air enters the intake
manifold. As the air approaches the intake valve, an
injection valve opens in the intake port, spraying
fuel into the airstream. Also called port injection.
MULTIPLE-VISCOSITY OILAn engine oil that
has a low viscosity when cold (for easier starting)
and a higher viscosity when hot (to provide
adequate engine lubrication).
NEEDLE VALVEA small, tapered, needle-pointed
valve that can move into or out of a seat to close or
open the passage through it. Used to control the fuel
level in the carburetor float bowl.
NITROGEN (N)A colorless, tasteless, odorless gas
that constitutes 78 percent of the atmosphere by
volume and is a part of all living substances.
NITROGEN OXIDES (NOx)Any chemical
compound of nitrogen and oxygen; a basic air
pollutant. Automotive exhaust emissions levels of
nitrogen oxides are limited by law.
NOZZLEThe opening or jet, through which fuel or
air passes as its discharged. Also, the assembly of
parts employed to atomize and deliver fuel to the
NOZZLE AND HOLDER ASSEMBLYThe
complete apparatus which injects the pressurized
fuel into the combustion chamber.
NOZZLE TIPThe extreme end of the nozzle body
containing the spray holes.
OCTANE RATINGA measure of the antiknock
properties of gasoline. The higher the octane rating,
the more resistant the gasoline is to spark knock or
OILA liquid lubricant, usually made from crude oil
and used for lubrication between moving parts.
OIL CLEARANCEThe space between the bearing
and the shaft rotating within it.
OIL CONTROL RINGSThe lower ring or rings on
a piston; designed to prevent excessive amounts of
oil from working up into the combustion chamber.
OIL COOLERA small radiator that lowers the
temperature of oil flowing through it.
OIL FILTERA filter that removes impurities from
the engine oil passing through it.
OIL GALLERYA pipe or drilled passageway in the
engine used to transport oil from one area to
OIL-LEVEL GAUGEThe dipstick that is removed
and inspected to check the level of the oil in the
crankcase of an engine.
OIL PANThe lower part of the crankcase in which a
reservoir of oil is maintained.
OIL-PRESSURE INDICATORA gauge that
indicates (to the operator) the oil pressure in the
lubricating system, or a light that comes on if the oil
pressure drops too low.
OIL PUMPA device that forces oil from the oil pan
to the moving parts of an engine.
OIL SLINGERA device mounted to a revolving
shaft such that any oil passing that point will be
thrown outward where it will return to the point of
OVERHEAD CAMSHAFTA camshaft located in
the cylinder head where the cam lobes are in direct
contact with the rocker arms.
OXYGENA colorless, tasteless, odorless, gaseous
element that makes up about 21 percent of the air.
Capable of combining rapidly with all elements
except the inert gases in the oxidation process
PARTICLEA very small piece of metal, dirt, or
other impurity which may be contained in the air,
fuel, or lubricating oil used in an engine.
PASSAGEA small hole or gallery in an assembly or
casting through which air, coolant, fuel, or oil
PCV VALVEThe valve that controls the flow of
crankcase vapors in accordance with ventilation
requirements for different speeds and loads.
PETROLEUMThe crude oil from which gasoline,
lubricating oil, and other such products are refined.