Agricultural Mechanics 8208-A Operation and Service of Gasoline Fuel Systems PDF

# AGRICULTURAL MECHANICS 8208-A ## OPERATION AND SERVICE OF GASOLINE FUEL SYSTEMS ### INTRODUCTION Almost all the engines used in modern agricultural equipment use some type of petroleum product as a source of fuel. Gasoline, the most common of these products, is the fuel of choice for automobiles...

# AGRICULTURAL MECHANICS 8208-A ## OPERATION AND SERVICE OF GASOLINE FUEL SYSTEMS ### INTRODUCTION Almost all the engines used in modern agricultural equipment use some type of petroleum product as a source of fuel. Gasoline, the most common of these products, is the fuel of choice for automobiles, light trucks, lawn and garden tractors, and auxiliary farm equipment. Lawn tractors up to 20 horsepower are about the limit of new gasoline-fueled tractors sold today; new farm tractors run on diesel fuel. However, auxiliary agricultural power sources usually run on gasoline. Portable generators, welders, sprayers, pressure washers, and pumps are typical examples of auxiliary power source applications in agriculture. Gasoline is actually a mixture of four different petroleum products which are blended together. The amount and type of base products mixed together determine the volatility* and the octane rating of the gasoline. Volatility measures the ability of a liquid to change from a liquid to a vapor. The lower the temperature at which liquid changes to vapor, the more volatile it is. Octane ratings usually range from the mid 80's to the mid 90's, and refer to the anti-knock quality of a gasoline, or its ability to resist detonation during combustion. In general, the antiknock ability of a gasoline is controlled by the speed at which the fuel burns. Gasoline with a low octane rating burns faster than high octane ratings, increasing the chance of causing engine "knock." "Knock" or pre-detonation causes excessive wear on piston heads, plugs, valves, and valve seats. Unleaded regular gasoline generally has an octane rating of 86 to 87. Small gasoline engines such as lawn mowers and weed-eaters often suffer from excessive plug fouling with low octane gasoline. Some studies indicate that small engines can last up to three times as long simply by using gasoline with octane ratings of 90 or higher. Various additives are used to help gasoline perform better in the engine, protect it during storage, burn cleaner, and protect the parts of the fuel system. The main responsibility of the gasoline fuel system is the delivery of a combustible mixture of fuel and air to the engine. If the system does not function properly, the engine cannot receive the amount of fuel required for it to operate. IMS student topic # 8794-D will provide additional information on fuel quality and selection. ### GASOLINE FUEL SYSTEM COMPONENTS Most gasoline fuel systems use five basic parts to supply the engine with the proper amount of air/fuel mixture. They are: 1) the fuel tank, 2) the fuel pump, 3) the carburetor, 4) fuel lines, and 5) a fuel filter or sediment bowl. The fuel tank stores the gasoline on the equipment for use in the engine. The fuel pump moves gasoline from the fuel tank to the float chamber of the carburetor. Fuel pumps are not needed when the fuel tank is located above the engine, since gravity will cause the fuel to flow to the engine. Most systems have some type of fuel filter which removes water, foreign materials, and other contaminants from the gasoline before it gets to the carburetor. Some fuel systems also have a sediment bowl as part of the fuel system. It functions similarly to the fuel filter, however it removes only the larger particles of debris and allows them to collect in the bottom of the bowl. If the bowl is not cleaned regularly, the flow of fuel to the carburetor will be reduced or blocked. - Intake Manifold - Fuel Tank - Carburetor - Governor, Linkage - Fuel Filter - Fuel Pump - Fuel Line The fuel lines carry fuel from the fuel tank, through the other components of the system, to the carburetor. The carburetor serves two main functions. It is responsible for: 1) the atomizing of the fuel for the engine and 2) the mixing of the atomized fuel with air in the proper ratio. The types and designs of carburetors vary from manufacturer to manufacturer, however they all have the same basic parts. The following is a list of the basic parts of a carburetor. 1. Throat - the tube through which air is drawn into the engine, and where fuel and air are mixed. 2. Venturi - a flow restriction, or narrowed part, in the throat tube. The restriction causes an increase in the speed of the air flow as air flows through the venturi. The venturi effect also lowers the pressure of the air flow on the other side of the restriction as the throat tube returns to normal size, causing air flow speed to decrease. 3. Throttle valve - located past the venturi, controls the amount of fuel/air mixture passing through the throat tube. 4. Bowl or Float chamber - a cavity in the carburetor where fuel is stored to be used as needed. 5. Jet - a small adjustable orifice past the venturi through which fuel is forced as it is sprayed into the air stream. 6. Choke valve - located before the venturi and is a means of closing off the throat. The choke valve reduces air flow and provides a rich air/fuel mixture for cold starting. 7. Float valve - controls the flow of fuel from the tank to the carburetor to maintain a constant level of fuel in the bowl. - Venturi - Throttle Valve - Jet - Float Chamber - Throat - Choke Valve In order for gasoline to be properly combusted, it must be atomized, vaporized, and mixed with air in the proper amounts. This is all done by the carburetor in normally aspirated engines. Air is drawn into the engine through the throat of the carburetor and by the intake stroke of the piston. As the air passes through the throat of the carburetor, it reaches a narrowed area called the venturi. The venturi causes the air speed to increase, and the air pressure to decrease. The low pressure air then draws air from the float bowl, through the jet, and into the air stream. The jet atomizes the gasoline as it enters the air stream. This breaks the gasoline into smaller particles, which enhances the vaporizing of the fuel. Once the air is mixed with air it vaporizes into even smaller particles which can be efficiently burned by the engine. Gasoline carburetors function differently as engine speed changes. When the engine is idling, the throttle valve is barely open, and the air does not flow fast enough to create a sufficient vacuum at the venturi to draw fuel from the main jet. An idle jet is used to provide the small amount of fuel required for the engine to idle. It is placed just past the throttle valve, since the vacuum has shifted to that point. The idle jet will provide enough fuel to create approximately a 10 to 1 air/fuel mixture. As engine speed is increased, the throttle valve partially opens to increase the amount of air passing through the venturi. This increase in air flow increases the amount of vacuum created by the venturi and some fuel is drawn through the main jet as well as the idle jet. A air/fuel mixture of approximately 12 to 1 is supplied. At high speed, the throttle valve is fully open and air flow is only restricted by the venturi. This shifts the vacuum to the venturi, and only the main jet is used to supply fuel. An air/fuel mixture of about 15 to 1 is provided to the engine. The amount of fuel which is allowed to pass through the jets is controlled by needle valves. The needle valves can be opened to increase the volume of fuel the air/fuel mixture, and produce a richer mixture. A rich mixture has a higher than normal portion of fuel in the air/fuel mixture. A rich mixture is said to be one that is 9 parts or less air to 1 part fuel. An extremely rich mixture can cause: 1) decreased engine efficiency, 2) carbon deposits to form in the cylinders, 3) valve burning, and 4) reduced power. The needle valves can be closed to decrease the volume of fuel the air/fuel mixture, and produce a leaner mixture. A lean mixture has a lower than normal proportion of fuel in the air/fuel mixture. Lean mixtures normally have at least 17 parts air to 1 part fuel. Although an operator may sometimes want an engine to run lean or rich to compensate for different operating conditions, a lean or rich mixture usually means that there is a problem in the carburetor. The technical or operator's manual will provide detailed information concerning the adjustment and maintenance of carburetors for a specific piece of equipment. Refer to IMS student topics #8793-A, #8793-B, and #8793-C for additional information about carburetion and fuel system components. The amount of air/fuel mixture allowed into the intake manifold or cylinders in controlled by the throttle valve. The operator can increase or decrease speed or power by moving the throttle control lever, or accelerator. When an increase in the engine's output is needed, the valve is moved to a position where it creates the least amount of resistance. To reduce the output of the engine, the valve is moved to a position which will restrict the amount of air/fuel mixture entering the engine. The throttle valve may also be controlled by the governor's action if the engine is equipped with one. A governor is a device which is used to control the speed or RPMs of a piece of equipment. Some engines are equipped with a governor which allows the equipment to be operated at uniform speeds and prevents the engine from being damaged by excessively high RPMs should the load be suddenly removed or decreased. The most common types of governors are: 1) vacuum, 2) centrifugal, 3) wind vane or pneumatic, and 4) hydraulic. While each of these governors differs in the means by which they gauge the speed of the engine, they all operate on the same basic principle. As an engine operates it creates centrifugal force, or vacuum, pneumatic, and hydraulic pressures. Each of the governors listed above uses one of these forces or pressures to equal the tension created by the throttle spring. (See the illustration on page 5.) The throttle spring is used to connect the throttle valve and the governor. When the throttle valve is opened to increase the power output of the engine, the throttle spring is stretched. As the spring is stretched, the tension it creates is increased. The governor uses the force or pressure created by the engine to equal the amount of tension created by the spring and maintain a constant speed. In other words, the governor is acting as a balance between the tension of the throttle spring and the force or pressure of the engine. This process is called "hunting," due to the fact that the governor is actually hunting for the proper amount of force to equal the tension of the spring. At this point the engine RPM will remain constant. If an additional load is applied to the engine, the RPMs will decrease, causing the engine force or pressure to decrease. The spring tension from the spring on the opposite side of the throttle will then pull the throttle valve open to provide additional air/fuel mixture. - Throttle (Butterfly Valve) - Governor Control Spring - Throttle Lever - Governor Lever - Open/Closed - Speed Control Lever - Engine Camshaft - Governor Flyweights - Throttle (Butterfly Valve) - Governor Control Spring - Throttle Lever - Governor Arm - Governor Drive Plate - Flyweights Lever - Governor Flyweights - Governor Drive Plate - Governor Arm - As Engine Speeds Up Governor Stabilizes It - Speed Control Lever Changed To Higher Speed Setting This allows the engine to increase power output to compensate for the additional load. Once the engine has returned to the desired RPM, the governor will again "hunt" for the position where the force or pressure from the engine will again equal the tension of the throttle spring. If part of the load is removed, or maximum engine RPMs is reached, the throttle spring is stretched to a point where the tension it creates causes the governor's linkage to close the throttle valve, and slow the engine down. This point is usually predetermined by the equipment manufacturer and should not be adjusted without consulting a manufacturer's representative or your local equipment dealer. The centrifugal type governor has been one of the most widely used types of governors on agricultural equipment. This type of governor uses a set of flyweights, which are spun by the engine, to create a balancing force against the throttle spring. - Governor Flyweights - Centrifugal Governor When the throttle lever is opened to increase engine output, the governor control spring, or throttle spring, is stretched to create tension. The tension created by the spring moves the throttle lever and opens the throttle valve, which allows engine speed to increase. However, as the engine speeds up, the flyweights are thrown outward by centrifugal force. The flyweights are designed so that as they move outward, they push the governor plate in. This action also moves the throttle lever, but it closes the throttle valve and slows the engine. As the engine slows down, the centrifugal force is decreased, and the flyweights move in until the force they exert on the governor plate equals the tension of the throttle spring. If an additional load is applied to the engine, the flyweights will move inward, allowing the throttle spring to move the throttle lever and open the throttle valve. As the engine speed increases, the centrifugal force increases, and the flyweights will move back out until they once again equal the tension applied by the throttle spring. Additional information concerning the operation of governors can be found in IMS student topics # 8793-B and # 8793-C. ### ELECTRONIC FUEL INJECTION SYSTEMS The carburetor systems that have been used in the past have been reliable and relatively efficient methods of supplying fuel to the engine. The engines in most new agricultural equipment use an electronic fuel injection system, rather than a carburetor, to create the air/fuel mixture which is utilized by the engine. Electronic fuel injection systems create and control this air/fuel mixture in a very precise manner. The use of fuel injection systems is due to Environmental Protection Agency requirements and because the Department of Transportation, by act of Congress, periodically increases requirements for vehicle efficiency and economy. Some of the advantages of electronic fuel injection systems are: 1) improves fuel atomization, 2) better fuel distribution, 3) provides a smooth idle, 4) improves fuel economy, 5) generates fewer harmful emissions, 6) better cold temperature operation, and 7) increased engine power. These advantages, as well as the actions of government agencies and consumer demands, have caused equipment manufacturers to increase the use of electronic fuel injection engines. All new passenger cars and trucks use electronic fuel injection, as well as many ATV's and outboard motors. Electronic fuel injection systems use an injector fuel pump and one or more injectors, rather than a carburetor and jets, to atomized gasoline and create the air/fuel mixture. Injection systems are classified by where the injectors release the gasoline in the engine. In simplest terms, a fuel injector is a spray nozzle combined with a solenoid operated plunger. The three basic types of electronic injection systems are: 1) throttle body injection, 2) port injection, and 3) direct injection. Throttle body injection systems are also called central injection systems (CFI), since fuel is only injected at one point. The throttle body injection system is the simplest form of fuel injection. This system usually has one injector which releases the atomized fuel into a carburetor-like device called a throttle body. Port and direct injection systems can also be classified as multi-point injection systems (MPFI), due to the fact that fuel is injected at multiple points. The air/fuel mix then passes through the intake manifold and into the cylinders to be combusted. Probably the most efficient method of gasoline injection is the port injection system. Port injection systems use multiple injectors, usually one per cylinder, to atomize the fuel. The injectors are usually located close to the intake port for each cylinder. This type of system allows the intake manifold to be designed for maximum airflow, since no consideration needs to be made for the air/fuel mixture. - Injection Nozzles - Injection Pump - High-Pressure Fuel - Low-Pressure Fuel - Gravity-Pressure - No-Pressure - Fuel Return - Filters - Fuel Tank - Fuel Pump - Direct Injection System Direct injection systems are the least commonly used type of gasoline injection system, however they are widely used with diesel engines. This system places the fuel directly into the combustion chamber. This method usually does not allow the atomized gasoline enough time to vaporize and blend with the air. Within each of the three types of injection systems there are two methods of operation. Continuous fuel injection delivers a constant flow of fuel to the injector nozzles. The volume of the fuel flow is altered to match the volume of the air flow, thereby maintaining the proper air/fuel mixture. Pulsed fuel injection uses fuel injection nozzles which are opened and closed by electronic or mechanical signals. The length of time the nozzle is open determines the amount of fuel that is sprayed into the incoming air flow. Just as with carburetor fuel systems, electronic fuel injection systems will have a fuel tank, fuel lines, fuel filter, and fuel pump. The fuel pump used in injection systems is normally referred to as the fuel transfer pump, however it functions the same way as it does in carburetor systems. In addition to these components, fuel injection systems have specialized components which are not found in carburetor fuel systems. These components are: 1) the injector pump, 2) injector nozzles, 3) various sensors, and 4) a central processing unit (computer) which helps to control the operation of the injection system. The injector pump meters and delivers gasoline to the injectors at the proper time. There may be one pump for the entire system or each injector nozzle may have its own pump, depending on the design of the system. The injector pump receives fuel from the fuel filter, increases its pressure, and delivers it to the injector nozzles at the proper time. Some electronic fuel injection (EFI) systems return unused gasoline to the fuel tank, helping to increase fuel economy. - Spindle - Pressure Spring - Body - Nozzle Valve - Spray Tip - Injector Nozzle The injector nozzles are responsible for the atomizing and spraying of the gasoline into the throttle body, intake manifold, or cylinder, depending on the type of system they are used in. The basic parts of an injector nozzle are the: 1) body, 2) nozzle valve, 3) spray tip, and 4) pressure spring. Pressurized fuel enters the body of the injector, which is closed on one end by the nozzle valve or pintle. Tension from the pressure spring holds the pintle shut until an electronic signal is received from the computer. The electrical connection receives the signal from the computer, and activates a solenoid which charges a coil that opens the pintle. Once the pintle opens, fuel is sprayed through the spray tip into the proper area. The amount of pressure on the fuel, and the size, number, and angle of the holes in the spray tip can be varied to obtain the desired spray pattern. Equipment manufacturers recommend different spray patterns for their various types of machinery, depending on the type of system used as well as the size and design of the engine used to power their equipment. ALWAYS CONSULT THE OPERATOR'S OR TECHNICAL MANUAL BEFORE SERVICING OR REPAIRING AN ELECTRONIC FUEL INJECTION SYSTEM!! Since the delivery of the fuel is more precise in injection systems, a series of sensors are needed to ensure that the proper amount of fuel is being delivered to the injectors, and that the system is operating correctly. The basic duties of the sensors are to monitor: 1) engine temperature, 2) load, 3) RPM, and 4) air intake. The following list describes some of the sensors used to monitor the operation of an injection system. 1. Exhaust Gas or Oxygen Sensor - relates amount of oxygen in the exhaust gas to indicate engine running condition and fuel mixture use. 2. Manifold Pressure Sensor - measures engine vacuum or pressure to determine engine load and relates this to the computer. 3. Throttle Position Sensor - relates the opening of the throttle valve to the computer to indicate the power need and air flow of the engine. 4. Coolant Temperature Sensor - reports engine temperature to the computer to help calculate the air/fuel for normal operation or cold engine start-up. 5. Airflow Sensor - indicates how much air is entering the engine and is used to help the computer calculate fuel delivery. 6. Air Inlet Temperature Sensor - relates the temperature of incoming air to the computer to regulate the air/fuel mixture. 7. Crankshaft Position Sensor - indicates piston position to time the spray of the fuel and helps calculate engine speed or RPM. - An Electronic Control Unit Each of these sensors are connected to an onboard computer called the electronic control unit (ECU) which serves as the "brain" of the electronic fuel injection system. The ECU receives information from all of the sensors, processes it, and calculates when and how long to open the injectors. The injectors are opened by sending an electronic signal to the solenoid on the injector which causes the injector valve to open. Some manufacturers have designed systems which open all of the injectors at the same time, regardless of whether the intake valves are open or closed. Some of the more efficient systems will open the injectors in several groups of two or more. This method increases efficiency, since more of the intake valves are open when the injectors are activated. The most efficient, and expensive, method of timing the injection of fuel is to open each injector as the intake valve for each cylinder opens. This type of system is used on high performance engines. The description of electronic fuel injection in this topic is a simple one, and some systems will have more components and sensors than have been described. The variation between systems and the complexity of the electronic controls, as well as the many additional pieces of diagnostic equipment and tools required to service and repair these systems, make working on electronic fuel injection systems difficult for the average owner or operator. Maintenance procedures for injection systems are outlined in the owner's or technical manual and should be closely followed. If a part failure or system malfunction occurs which is not covered in the owner's or technical manual, and the owner or operator has not been trained to repair injection systems, a trained service technician should be contacted to repair the system. There are some additional safety factors which must be remembered when working with injection systems. Never check for leaks in an injector system with your bare hand. The injector pump creates enough pressure to allow fluids to deeply penetrate the skin, and cause a very serious infection if proper medical attention is not given immediately. Also, never check the operation of the injector nozzle without some sort of eye protection. If the injector nozzle opens and sprays fuel, it can very easily get into your eyes and damage them. Additional safety precautions can be found in the owner's or operator's manual and should be read before servicing or repairing an injection system. ### GLOSSARY OF TERMS - Electronic control unit - an onboard computer or brain for an electronic system - Octane rating - a fuel's measure of resistance to detonation during combustion - Volatility - the ability of a liquid to change from a liquid to a vapor ### References - Technical Bulletin, Chevron Oil Company. - Electronic Fuel Injection, Ford Motor Company, Parts and Service Division, Detroit, MI. - Fundamental of Machine Operation: Preventive Maintenance, Deere and Company, Moline, IL. - Fundamental of Machine Operation: Tractors, Deere and Company, Moline, IL. - Fundamental of Service: Fuels, Lubricants, and Coolants, Deere and Company, Moline, IL. - Jacobs and Harrell, Agricultural Power and Machinery, McGraw - Hill, New York, NY. *Underlined words are defined in the Glossary of Terms.