Glossary of terms, and system theory
- 49-State Car- See CA
- AIS- Air Injection System- Air Injection defines a system that
introduces fresh air to the
stream. This has been used in many ways, but the primary reason is to
help raise the exhaust
temperatures, promoting continued combustion of the exhaust gases as they
leave the system.
Air can be
introduced either by way of a belt-driven air pump, or by the natural
vacuum that occurs when
moving exhaust gases pass an open port. The latter style is usually
called reed valve or
Pulse Air Injection. In early cars, a thermactor system was
used- This basically allowed
(partially unburned) gases leaving the exhaust valves a fresh shot of
air, causing them to 're-
burn' as they
left the manifold. Heat was again a primary function in later cars using
catalysts, as the catalyst
reach operating temperature before it an do its job (see
Catalyst), and the fresh shot of
also helps the chemical reaction inside the catalyst. An important
note: Most air pumps use less
.5HP at peak load- the plumbing associated with these systems can be a
headache, but the
performance losses are minimal. Indeed, some long-term Fiat mechanics
tout the air injection,
keeps the exhaust valves cooler, prolonging the life of the engine. Make
your own judgment.
- Breather- The breather system seals crankcase blow-by gases and
routes them to the intake
combustion. Most cars use a vacuum operated PCV system to accomplish
this- Fiat, and some
European cars were the last to use a passive breather system in their
- CA- California certified car. These days, most cars are built to
states have stringent emission control regulations. In the past, some
manufacturers had specific
built to pass regulations for sale in California, because CA regulations
were so much more
stringent at the
time. Cars not built to California spec. were called Federal, or
49-State cars. This was done
save money in those US states where extensive emissions control equipment
was not required.
- Catalyst- An exhaust device that uses a chemical reaction to reduce
- Charcoal Canister- See EVAP
- Check Valve- A one-way valve, usually found in Air Injection systems.
- CO- Carbon Monoxide- Odorless, colorless and toxic, this gas is a
major byproduct of
- EGR- Exhaust Gas Recirculation- EGR is a system whereby a small
amount of exhaust gas
redirected to the intake stream, under certain load and temperature
conditions. This is not done
the gas (as is widely thought), but to lower overall combustion
temperatures. Lower combustion
temperatures reduce the amount of NOX produced during the combustion process.
- EVAP- Evaporative fuel emission controls- Many systems exist, but the
concept is to reduce
amount of raw hydrocarbons that are emitted when an open fuel tank
'perks' as its temperature,
density changes. Most systems use a charcoal vapor canister to trap the
vapors when the car is
and slowly vent those vapors to the intake when the car is running.
- Federal- See CA
- HC- Hydrocarbons- Basically the chemical term for unburnt fuel.
- NOX- Nitrous Oxides- A byproduct of high-temperature combustion, NOX
is produced when
Oxygen, and Nitrogen present in the intake stream combine under pressure,
and heat. NOX is a
contributor to atmospheric problems associated with smog.
- O2 Sensor- Device that converts oxygen content present in the exhaust
stream to a voltage
usually between 1.0-1.5 volts. This voltage signal is used by the ECM to
help determine mixture.
sensors need to reach operating temperature before they start to operate,
and do wear out over
used O2 sensors on the fuel-injected models, see your service manual for
- O2- Oxygen
- OC- Oxidizing Catalyst- The catalytic converter is a device that,
under relatively high heat
degrees+ F.) utilizes a chemical reaction to convert Oxygen, Hydrocarbons
water vapor and Carbon Dioxide. The catalyst is filled with a substrate
of precious metals,
platinum and palladium, with the addition of rhodium in some cases- Early
catalysts have loose
inside them (some of which allow you to change the substrate if you have
access to new pellets),
style have a honeycomb style 'brick' inside them. Most Fiats here have
an early OC- Carbureted
the original 3-bolt flange style Cat, and Fuel-Injected cars got the
4-bolt flanged Cat.
- PAI- Pulse Air Injection- See AIS
- TAC- Thermostatic Air Cleaner - This system directs heated air
(usually picked up by a
stove on the
exhaust manifold) to the induction system to aid in warm-up. Refer to
your vacuum diagram.
have a simple thermovalve that inhibits vacuum when cold, allowing a
the cold air side of the air cleaner to shut. When the car warms up,
vacuum is allowed to draw
open, allowing fresh cold air to the air cleaner. Some cars,
(specifically pre-'79 carbureted Fiats)
manual climactic setting, allowing you to change the position of the air
cleaner with the season.
allows warm air all the time in one position, and cold in the other.
- TPS- Throttle Position Sensor- Sends information (usually a
resistance figure through a
potentiometer) to the ECM regarding throttle plate opening. Fiat
application only on the Injected
- TVS- Thermal Vacuum Switch- A favorite of Fiat, this device either
closes off or allows the
vacuum based on coolant temperature. Most often used in spark control or
circuits, they go
- Vacuum Advance- Controls ignition timing based on manifold (or
- Vacuum, Manifold- Vacuum source in manifold below throttle plate.
- Vacuum, Ported- Vacuum source in carburetor above throttle plate.
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