The first emission device to be required by law was one that prevented (Crankcase Blowby) (blowby-Byproducts of combustion that leak out of the combustion chamber past the piston rings into the crankcase. mostly hydrocarbons, this represents approximately 20% of the air pollution a pre-emissions controlled engine produces. In modern vehicles, the blowby vapors are drawn into the intake stream through the positive crankcase ventilation system to be burned in the cylinders. Vapors from escaping into the atmosphere. It was called "Positive Crankcase Ventilation"(PVC), and today you will find it under every hood.
Prior to the introduction of PCV systems, crankcase blowby gases were dumped into the atmosphere through a "road draft tube." Fresh air entered the crankcase through an open breather cap on the oil filler tube. The fresh air then circulated through the engine, and exited through the road draft tube along with moisture and blowby gases from the crankcase. It was not very effecient method of venting the crankcase, nor did it help the growing air pollution problem. In fact, prior to PCV, nearly 20% of the pollutants vehicles dumped into the atmosphere came from open crankcases.
Positive crankcase ventilation prevents crankcase blowby vapors from escaping into the atmosphere by siphoning the vapors back into the intake manifold. Then the the blowby vapors can be reburned in the engine. The open road draft tube is replaced with a hose that reroutes the vapors back to a vacuum port on the intake manifold or under the carburetor. Fresh air is pulled through the engine by intake vacuum, and along with it the blowby vapors and moisture from the crankcase. Airflow through the PCV system is metered by the PCV valve. This PCV valve is a spring loaded variable orifice valve that changes the flow rate according to engine load and throttle position.
On some vehicles, a small PCV air filter is mounted inside the air cleaner. This filter should always be inspected, on a regular basis. On other vehicles, the crankcase vent is located on the inside of the air filter, so a seperate filter is not used.
Besides eliminating crankcase blowby vapors as a source of air pollution, PVC also reduces the buildup of moisture in the crankcase. The PCV prolongs the life of the oil as well. If the PCV valve or hose becomes clogged, moisture can rapidly accumulate in the crankcase, leading to slugde formation. And if the oil isn't changed often enough, sludge can ruin the engine! Thats why regular inspection of the PCV system is important.
A clogged PCV system will also allow pressure to build within the crankcase, possibly forcing oil to leak past gaskets and seals.Oil vapor backing up into the air cleaner, might be symptons of a clogged PCV system. Regular inspection and periodic replacement will keep the system functioning properly.
The other problem to watch out for with PCV systems are vacuum leaks. Because the PCV valve acts like a calibrated vacuum leak, any additional air leaking past the valve can lean out the air/fuel ratio. This results in lean misfire, hesitation, hard starting, and stalling. Watch for cracked or loose hoses , or poorly fitting valves. The PCV valve must be the correct one for the aplication. The wrong valve may flow too much or too little air, upsetting the fuel calibration.
(EVAP) EVAPORATIVE EMISSIONS CONTROL
Gasoline fuel vapors, or evaporative emissions, as they are called , contain a variety of Hydrocarbons (HC). The lighter elements in gasoline evaporate easily, especially in warm weather. These include Aldehydes, aromatics, olefins, and higher paraffins. These substances can react with stale air and sunlight (called a photochemical reaction) to form SMOG. Evaporative emissions can also account for 20% of a vehicles total emissions. A parked car can pollute the air with Hydrocarbon emissions even though the engine is not running, so you should appreciate the importance of controlling evaporative emissions. The problem becomes especially bad on hot summer days when the vehicle is parked in the sun on an open parking lot. The gasoline vapors can literally spew out of the vehicle's fuel system wasting gas, unless they are prevented doing so by an Evaporative emission control system.
Evaporative emissions are eliminated by sealing off the fuel system from the atmosphere. This prevents the gasoline vapors from escaping from the fuel tank or carburator bowl. Vent lines from the fuel tank and carburator bowl route vapors to a charcoal canister. They are trapped and stored there until the engine is started. The vapors are then drawn into the intake manifold and burned with the mixture.
With fuel injection, there are no evaporative emissions from the engine compartment because the injectors are part of a sealed system. Unlike a carburator, there is no vented fuel bowl to leak vapors. The fuel is all contained within the pressurized fuel rail and injectors. But the fuel tank must still be sealed to prevent vapors from escaping out the filler pipe.
(EEC)Evaporative Emission Control Components
- Fuel Tank- All fuel tanks in today's cars are designed to allow for fuel expansion. The expansion space is usually 10 to 12% of the total tank volume. For example, a tank designed to hold 12 gallons of fuel, when filled, would need at least an additional 1 gallon capacity for expansion space can be designed into a fuel tank. The easiest way is to locate the filler neck. An air space is then created at the top of the tank when it is filled. Designing a bulge or dome on the top of the tank serves the same purpose. The air pocket absorbs the increase in volume, as the fuel expands.
Another way to create an air space in the top of the tank is to connect a fill control tube to the filler neck. When the tank reaches a certain level as it is being filled, gasoline begins to flow back through the fill control tube into the filler neck. This causes the gas nozzle to kick off and prevents overfilling the fuel tank. The remaining air space at the top of the tank then serves as the expansion reserve.
The only problems any of these expansion control techniques can create are complaints about bslow filling. Many motorists quickly discover that such fuel tanks fill slowly, or that they never seem to be quite full. That is because the tanks are designed that way. Overfilling, by continually squeezing in a few more cents' worth of gasoline after the nozzle has kicked off, defeats the designed purpose of expansion control.
- Gas Cap- Most people dont relize the gas cap is an emission control device, but it is. In precontrol days, the gas cap's main job was to keep gasoline from sloshing out of the tank, and dirt from getting in the tank. It was equipped with a small vent hole so that the tank could breathe. Air entered through the cap to make up for fuel as it was used, and fuel vapors exited through the cap as internal pressure rose on warm days.
Todays emission control gas caps are considerably different. They are either of a solid construction(venting is provided by other means) or they contain a pressure/vacuum valve. The valve type cap will vent tank pressure if it exceeds 1 psi.It will also allow air to enter the tank if a vacuum exists within the tank. In other words, the valve type cap can vent pressure or releive vacuum as the situation warrants without allowing gasoline vapors to pollute the environment.
The valve itself is a simple double spring arrangement similar to a radiator cap. One spring reacts to internal pressure while the other reacts to external pressure. A plate or diaphragm between the two springs opens and closes to allow air to pass through the valve in the direction needed.
Internal fuel tank pressure can be also vented by means of a three way valve in a vapor line to the charcoal canister. Some ford vehicles do not have a pressure/vacuum releif gas cap. Instead they use a three way valve in the fuel tank vent line to control internal tank pressure. The valve vents tank pressure to th charcoal canister. When there's a vacuum in the tank, the upper diaphragm will allow air to be drawn into the vent line to the tank. The lower diaphragm serves as a safety vent for excessive tank pressure in case the main vent line becomes clogged.
If a gas cap has to be replaced on a vehicle, the replacement must be the same type as the origanal(sealed or vented).
- Liquid vapor Separator- On top of the fuel tank or as part of the expansion tank is a device known as a liquid vapor separator. The purpose of th do not want liquid gasoline going directly to the charcoal canister because it would quickly overload the canister's ability to store fuel vapors.
The liquid vapor separator works on the principle that vapors rise and liquids sink. The vapor vent lines from the fuel tank, that go to the separator are positioned vertically inside the unit with the open ends near the top. This allows the vapors to rise to the top of the separator. Any liquid that enters the separator through the vent lines dribbles down the sides of the vent tubes and collects in the bottom of the separator. Examples of this are fuel sloshing around inside the fuel tank as a result of hard driving, parking on a steep hill, excessive fuel expansion, etc. A return line allows the liquid gasoline to dribble back into the fuel tank. The vapors then exit through an opening in the top of the separator. This opening which usually has an orfice restriction to help prevent any liquid from getting into the canister vent line.
The liquid vapor separator is a simple device that is relatively trouble free. One problem that can develop is if the liquid return line becomes plugged with debris, such as rust or scale from inside the tank. Another problem is if the main vent line becomes blocked or crimped. A third problem is if a vent line develops an external leak due to rust, corrosion, or metal fatigue from vibration.
If a blockage occurs in the liquid separator, or in the vent line between it and the charcoal canister, the fuel tank will not be able to breathe properly. Symptoms include fuel starvation, or a collapsed fuel tank on vehicles with solid type gas caps. If you notice a woosh of pressure in or out of the fuel tank when the gas cap is removed, suspect poor venting.
You can check tank venting by removing the gas cap and then disconnecting the gas tank vent line from the charcoal canister. If the system is free and clear, you should be able to blow through the vent line into the fuel tank. Blowing with compressed air can sometimes free blockage. If not, you will have to inspect the vent line and possibly remove the fuel tank to diagnose the problem.
- Charcoal Canister-The charcoal canister is a small round or rectangular plastic or steel container mounted somewhere in the engine compartment. On some late model vehicles where underhood space is a premium, the canister may be hidden behind a fender splash panel.
The canisters job is to store gasoline vapors from the fuel tank, so that the fumes do not pollute the atmosphere. The canister contains activated charcoal, wich weighs about 1-1/2 lbs. Charcoal acts like a sponge to soak up the gasoline vapors, holding up to twice its weight in fuel.
The vapors are stored in the canister until the engine is started. The vapors are then drawn into the air cleaner, through a vacuum port in the carburetor or intake manifold, or are siphoned into the engine through the PCV plumbing.
Some early Chrysler evaporative control systems did not use a charcoal canister. Instead, the fuel vapors were routed into the engine's crankcase for storage. When the engine was started, the PCV system would draw fumes out of the crankcase and into the intake manifold. This approach had its draw backs, though. For one thing, the gasoline vapors tended to dillute the crankcase oil. The vapors also formed an explosive mixture that could literaly blow the valve covers off the engine. Because of such problems, the approach was dropped in a favor of the charcoal canister method of storing fuel vapors.
The charcoal canister is connected to the fuel tank via the tank vent line, and to the carburetor bowl with another vent hose. The pressure, created by evaporating fuel, drives the vapors through the lines and into the canister. Here they stay until the canister is purged by starting the engine.
The auto manufacturers have been quite clever in coming up with varios ways to purge the canisters contents. Some canisters older vehicles have an open bottom with a small, flat air filter across the opening. The filter is there to keep dirt out of the canister, while it is being purged. On applications that use such a filter, the filter should be inspected periodically and replaced according to the manufacturer's recommendations. A good rule of thumb is to replace the filter every two years.
On canisters with the open bottom, fresh air is drawn in through the filter by connecting a purge line from the top of the canister to the air cleaner, a carburetor vacuum port, or the PCV plumbing. Air flow through the canister ("purging") is regulated by a purge control valve on the canister. The valveopens in response to a ported vacuum signal.Others use an electric solenoid purge control valve. On these systems, the solenoid is regulated by the engine control computer.On canisterswith sealed bottoms fresh air is circulated through the canister via a center tube, up through the charcoal, and out the purge line.
Depending on the design of the canister, purging may be controlled in different ways. Those that use ported vacuum use a technique called constant and demand purge. The purge valve on the canister allows constant purging at a restricted rate, through an orfice, until a certain level of vacuum exists at the canister outlet. When ported vacuum is applied to the purge control valve, it allows a higher purging rate. The reason for having constant and demand purging is because the engine cannot handle a large flow of air through the canister at idle or slow speeds. The addition air and fuel vapor would upset the air/fuel ratio, causing a rough idle and increased tailpipe emissions. At higher rpm rates, however, the engine can digest the canister's contents without problem. Purging is calibrated to match the engines ability to handle it A vapor feed rate of around 12 cubic feet per hour might be average for a small V8 cruising down the highway.
Under normal circumstances, the charcoal canister causes few problems. Since the charcosl canister does not wear, it should last the life of the vehicle. Problems can result, though, when the canister filter is neglected, or when a purge control valve malfunctions. A problem also occurs if someone gets the vent, purge, and control vacuum lines mixed up.(The connections are usually labeled to avoid such mistakes)
If vapor is not being purged from the canister, the purge valve may be defective or the canister filter may be plugged. The purge valve can be tested with a hand held vacuum pump, it should hold vacuum for at least 15-20 seconds without leaking down. Vacuum connections should be inspected to make sure that they are tight and properly routed,also the condition of the hoses. The electrical connections in the evap system should be checked for looseness, corrode terminals, and worn insulation of the wiring.
On units equipped with computer controlled solenoid purge valves, the manufacturer determines when and under what conditions, the solenoid is supposed to open. Generally speaking, such systems will not purge the canister until the engine reaches operating temperature. The coolant sensor monitors engine temperature, so when the computer reads the appropiate temperature, then it sends a command to open the canister purge solenoid.
- Anti-Percolator Valve-This is used to prevent evaporation from the fuel bowl during engine operation, some carburetors have an anti-percolator valve, where the canister vent line connects to the throttle linkage. It will be closed when the throttle is closed. The valve opens when the engine is off (The throttle closed), so that thehot fuel vapors can boil out through the vent line and into the canister.
The heated air intake, or early fuel evaporation system's purpose, is to preheat the air before it enters a carburetor when the engine is cold or first started. It does this by routing air through a "stove" around the exhaust manifold before it enters the air cleaner. A temperature sensor inside the air cleaner controls a vacuum diaphragm in the air cleaner inlet. When cold, the temperature sensor passes vacuum to the diaphragm. This closes a flap to outside air so heated air will be drawn into the air cleaner. Warm air improves fuel vaporization while the engine is warming up. This helps the engine idle morte smoothly. It also improves cold driveability by reducing the tendency to hesitate or stumble when the throttle is opened.
As the engine warms up, the air doesn't have to be heated as much. The temperature sensor (in the air cleaner) reacts to the rising temperatures and begins to bleed air. Spring pressure overcomes the vacuum diaphragm, and the air flow control door opens to admit more unheated air into the air cleaner. By reacting to changes in the incoming air temperature, the temperature sensor is then able to keep the carburetor with warm air. This makes it easier for the carburetor to maintain a consistant AIR/FUEL MIXTURE. Thats because air density changes with temperature. Cold air is more dense than warm air. When the air outside is cold (more dense), it has to be heated (made less dense) to prevent the fuel mixture from becoming too lean.
Driveability problems can arise when the heated air intake system fails to do its job properly. A missing, loose, or damaged heat riser tube connects the air cleaner to the stove on the exhaust manifold. This will prevent warm air from entering the air cleaner. A defective temperature sensor, vacuum leak, or faulty vacuum diaphragm in the air flap control motor, will likewise keep the system from functioning properly. And the result can be rough idle, hesitation, and poor cold driveability, while the engine is warming up (especially during cold weather).
If the the air control door is stuck in the closed position, a continuous supply of heated air is fed to the carburetor. The overheated air can then cause detonation (spark knock or pinging) during warm weather. The fuel mixture will also run rich because the air is too hot. This will have a negative effect on the fuel economy and emissions, especially on older engines that don't have electronic feedback carburetion.
A check of the heated air intake system should begin with a visual inspection of the components. 1:Such as the tubing between the air cleaner and stove on the exhaust manifold, should be tight and intact. 2:Also the air duct that routes outside air into the air cleaner, should be properly mounted and free from obstruction. 3:The air door inside the air inlet duct should be in the open position when the engine is off. It should also be open whenthe engine is idling at normal operating temperature during warm weather. 4:The air door should close to outside air when a cold engine is first started. The air door should then remain closed until the incoming air reaches a temperature of about 95-100 degrees F.
If the air door doesen't close when a cold engine is first started, check for a leak in the vacuum plumbing, a defective vacuum motor, or a faulty temperature sensor. If the door closes, but fails to open once the engine reaches normal operating temperature, the temperature sensor may me bad.
You can check the operation of the air control door by applying vacuum, with a hand held vacuum pump, directly to the vacuum motor on the air cleaner inlet duct. If the door fails to move, or if the motor can't hold vacuum, the rubber diaphragm inside the vacuum motor is leaking and the motor needs to be replaced.
The temperature sensor can also be checked with a hand vacuum pump. Leave the hose from the temperature sensor to the vacuum motor connected. Disconnect the vacuum supply hose to the sensor coming from the carburetor and apply vacuum directly to the sensor. The temperature sensor should pass vacuum on to the air door motor, as long as it is below about 95 to 100 degrees F. If a cold sensor leaks vacuum, replace it.
(AIS)Air Injection Systems
No matter how well an engine is designed to minimize emissions, a certain amount of unburned hydrocarbons and carbon monoxide will always be left in the exhaust as it exits the engine's cylinders. So some means of cleaning up the exhaust is needed to reduce or eliminate these pollutants once they've exited the engine.
Air binjection is just such a system. It first appeared 1968. Called AIR(air injection reaction) by GM and Thermactor by Ford , the name that stuck was "Smog Pump".
The basic idea behind air injection is to pump extra oxygen into the exhaust. It can then combine with the pollutants before they exit the tailpipe and enter the atmosphere. In the early days of pollution control (Before catalytic Converters), one approach that was taken was the thermal reactor. The thermal reactor was a very large and well insulated exhaust manifold used in conjunction with a high capacity air pump. This combination provided a furnace like environment in which the HC and CO was given a good opportunity to combine with oxygen to complete the combustion process in the exhaust. It was an inexpensive technology, but it wasn't very efficient. It raised underhood temperatures drastically. So along came catalytic converters.
The vwholesale adoption of the two way catalytic converter by U.S. auto makers in 1975 changed the purpose of air injection. It became the means for supplying extra oxygen to the exhaust, so the pollutants could be reburned inside the converter instead of just the manifold.
The mixture of oxygen from the air pump and HC and CO flares up in the presence of the catalyst. Temperatures as high as 1600 degrees F are generated, eliminating most of the harmful pollutants by oxidizing them into CO2 and water.
Some catalyst-equipped vehicles have been built that dont need air injection. These have engines calibrated in a way that there is enough O2 in the exhaust to support the reaction in the converter. But these are exceptions. Most vehicles today have either an air injection system or an aspirator-valve setup to provide the extra fresh air the catalyst needs to do its job.
- You'll find the following components in a typical air injection system:
- A belt driven vane pump.
- A vacuum operated diverter valve. This valve vents pump output to the atmosphere during deceleration, so the combination of a rich mixture and extra oxygen doesent cause an exhaust backfire.
- A pressure releif valve. This valve allows excess pump output to escape.
- A one way check valve. This valve allows air flow into the exhaust manifold, but keeps exhaust out of the pump if the belt breaks.
- The plumbing and nozzles necessary to distribute and inject the air.
- Air Pump-When the engine is started, a belt causes the pump pulley to rotate. inside the pump, vanes riding against the walls of a cylindrical chamber start moving air. The rotor turns on an axis thats different from that of the pump bore. The vanes slide in and out slots in the rotor. This causes a pumping action that moves air through the pump. Usually, intake is through a centrifugal filter mounted behind the drive pulley, but seperate intake filters have been used on some applications. Most systems use a releif valve that allows excess pump pressure to escape. It may be in the pump itself, or incorporated into the diverter valve. The pressurized air exits into a large diameter hose that routes it to this valve.
During all modes of engine operation except deceleration, air from the pump flows into the hose to the check valve. This is a simple oneway device, wich lets air enter the air injection manifold. This oneway device also keeps exhaust from backing up into the pump if a belt should break, or if the pump should otherwise stop working (normally the pump's pressure is high enough to overcome exhaust pressure). From the check valve, the air flows into the air injection manifold, which directs it into each exhaust port.
- Diverter Valve-The diverter valve is the most complicated part of the air injection system. The most common type receives a vacuum signal through a hose that runs to the intake manifold, or the base of the carburetor or throttle body. During closed throttle deceleration when the engine vacuum is the strongest(high vacuum), it directs air flow through a small muffler, which is usually mounted on the pump.
The valve has a vacuum chamber, diaphragm, and spring arrangement. This valve moves the stopper from one of its seats to the other, and so controls the switching operation. During deceleration, the diaphragm in the valve's chamber overcomes the force of the spring, and dumps air flow to the muffler. this prevents backfiring in the exhaust system. If the pump provides extra air, it would allow the rich mixture, that is present in the exhaust stream during deceleration., to ignite explosively. To put it simply, the diverter valve directs the air pump's output away from the exhaust system during deceleration.