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 exhaust 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 hot, 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 the hot (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 needs to reach operating temperature before it an do its job (see Catalyst), and the fresh shot of oxygen also helps the chemical reaction inside the catalyst. An important note: Most air pumps use less than .5HP at peak load- the plumbing associated with these systems can be a headache, but the actual performance losses are minimal. Indeed, some long-term Fiat mechanics tout the air injection, saying it 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 for combustion. Most cars use a vacuum operated PCV system to accomplish this- Fiat, and some other European cars were the last to use a passive breather system in their US-bound cars.
• CA- California certified car. These days, most cars are built to 50-State specification, because most states have stringent emission control regulations. In the past, some manufacturers had specific models 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 primarily to 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 harmful exhaust emissions. See OC.
• 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 combustion.
• EGR- Exhaust Gas Recirculation- EGR is a system whereby a small amount of exhaust gas is redirected to the intake stream, under certain load and temperature conditions. This is not done to reburn 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 the amount of raw hydrocarbons that are emitted when an open fuel tank 'perks' as its temperature, and density changes. Most systems use a charcoal vapor canister to trap the vapors when the car is parked, 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 major contributor to atmospheric problems associated with smog.
• O2 Sensor- Device that converts oxygen content present in the exhaust stream to a voltage signal, usually between 1.0-1.5 volts. This voltage signal is used by the ECM to help determine mixture. O2 sensors need to reach operating temperature before they start to operate, and do wear out over time. Fiats used O2 sensors on the fuel-injected models, see your service manual for test procedures.
• O2- Oxygen
• OC- Oxidizing Catalyst- The catalytic converter is a device that, under relatively high heat (400 degrees+ F.) utilizes a chemical reaction to convert Oxygen, Hydrocarbons and Carbon Monoxide into water vapor and Carbon Dioxide. The catalyst is filled with a substrate of precious metals, usually platinum and palladium, with the addition of rhodium in some cases- Early catalysts have loose pellets inside them (some of which allow you to change the substrate if you have access to new pellets), but later- style have a honeycomb style 'brick' inside them. Most Fiats here have an early OC- Carbureted cars had 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. Most cars have a simple thermovalve that inhibits vacuum when cold, allowing a vacuum-operated flapper valve on the cold air side of the air cleaner to shut. When the car warms up, vacuum is allowed to draw the flapper open, allowing fresh cold air to the air cleaner. Some cars, (specifically pre-'79 carbureted Fiats) have a manual climactic setting, allowing you to change the position of the air cleaner with the season. This 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 cars.
• TVS- Thermal Vacuum Switch- A favorite of Fiat, this device either closes off or allows the flow of vacuum based on coolant temperature. Most often used in spark control or EGR vacuum circuits, they go bad often.
• Vacuum Advance- Controls ignition timing based on manifold (or ported) vacuum.
• Vacuum, Manifold- Vacuum source in manifold below throttle plate.
• Vacuum, Ported- Vacuum source in carburetor above throttle plate.

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