CHAPTER 48 Gasoline Fuel Systems.

CHAPTER 48 Gasoline Fuel Systems

Introduction (1 of 2) Today’s gasoline fuel systems must meter a precise amount of fuel into the engine under a wide range of operating conditions. Optimizing engine performance while keeping fuel consumption and emissions to a minimum Carburetors were commonly used until 30 years ago. Electronic fuel injection (EFI) were introduced when mechanical fuel injectors couldn’t meet standards.

Introduction (2 of 2) Multipoint fuel injection (MPFI or PFI) was more prevalent as technology progressed. Gasoline direct injection (GDI) Places fuel injectors in cylinder head where they can spray fuel directly into combustion chamber An electronic control unit (ECU) or power train control module (PCM) is needed to determine proper quantity of fuel to be delivered.

Gasoline Fuel System Principles (1 of 7)
Fuel system provides ideal air–fuel mixture for operating conditions of the internal combustion engine. Fuel needs to be: Vaporized Mixed with the proper amount of air Atomized as small as possible

Modern gasoline-powered vehicles use EFI systems. Atomize the fuel into much smaller particles Carburetors cannot atomize fuel as efficiently as fuel injection systems. Pressure differential is central to all fuel systems.

Carburetor works off of pressures below atmospheric pressure (vacuum). Involves a low pressure differential

The main difference between carburetion and fuel injection is that carburetion works off of pressures below atmospheric pressure (vacuum), and fuel injection works off of pressures above atmospheric pressure.

Fuel injection works off of pressures above atmospheric. Involves a much higher pressure differential Fuel supply system Provides pressurized, filtered gasoline to fuel injectors or carburetors (in older vehicles) Draws in gasoline from gas tank (fuel cell) and delivers under pressure to fuel metering device Today’s vehicles typically use an in-tank electric fuel pump

Air supply system Also called induction system Provides clean filtered air for combustion in the engine An air filter is a paper filter or element that filters the incoming dirty/dusty air. Engineers have made numerous configurations to prevent water and dirt intrusion. Air intake sounds have been carefully analyzed.

Fuel metering system Constantly meters and adjusts amount of fuel that the engine is burning Multipoint fuel injection Although specific systems vary, many systems have similar parts.

Gasoline Fuel (1 of 9) Gasoline derived from crude oil
Taken from ground as a liquid mixture Highly flammable compounds of hydrogen and carbon together with impurities Called hydrocarbons

Gasoline Fuel (2 of 9) Hydrocarbon is processed into many fuel and lubricant products at an oil refinery. Fractional distillation process Gasoline is very volatile. Mixes easily with air to form gas or vapor The more effectively liquid gasoline is changed into vapor, the more effectively it burns in the engine. Highly volatility is desirable.

Gasoline Fuel (3 of 9) Gasoline vapor allowed to mix with air in the open is highly explosive. High volatility can create excessive hydrocarbon emissions. Vapor lock Fuel vaporizes in fuel pump Bubbles of vapor can block flow of fuel and stop the engine

Gasoline Fuel (4 of 9) Gasoline mixture
Paraffins Naphthenes Aromatics Olefins Some organic compounds and contaminants Sulfur Some countries have tight regulations limiting allowed proportion of aromatics, olefins, and sulfur in gasoline.

Gasoline Fuel (5 of 9) Gasoline in its raw processed form is not suitable for use in vehicle engines. Enhanced with different additives Detergents Octane boosters Oxygenates such as ethanol

Gasoline Fuel (6 of 9) Knocking, or pre-ignition
When a mixture of gasoline (petrol) and air is compressed inside an engine cylinder If compression is high enough and fuel is able to ignite easily, air–fuel mixture may spontaneously ignite before spark plug is fired at the optimum ignition moment.

Gasoline Fuel (7 of 9) Gasoline fuel can be modified during processing. Octane rating is measured by the producer. The Research Octane Number (RON) Motor Octane Number (MON)

Gasoline Fuel (8 of 9) Popular belief that fuels with higher octane ratings will improve performance in vehicles designed to run on fuels with lower octane ratings Largely a myth

Gasoline Fuel (9 of 9) Octane can be boosted with additives.
Tetraethyl lead was added to boost octane prior to the introduction of catalytic converters. Also used to lubricate valve faces and seats Slowed down wear Leaded fuel was phased out for general vehicle use. Octane is now boosted with additives of ethanol, aromatic hydrocarbons, and ethers.

Controlling Fuel Burn Gasoline must be mixed with the right amount of air to burn properly. A slightly lean mixture gives good fuel economy and low exhaust emissions.

Combustion (1 of 3) The spark plug ignites mixture and a small ball of flame forms around the tip of plug. Piston finishes compressing mixture. Flame spreads faster and moves evenly to halfway through mixture and piston reaches top dead center. Flame picks up more speed and shoots out to consume the rest of the mixture.

Combustion (2 of 3) Combustion ends with the piston a short way down the cylinder. Ideally this would completely burn all of the fuel that entered the cylinder.

Combustion (3 of 3) In normal combustion, the spark plug ignites the mixture, and a small ball of flame forms around the tip of the plug.

Detonation/Pre-ignition (1 of 4)
Detonation is a violent collision of flame fronts in the cylinder. Sudden rise in pressure can cause remainder of mixture to ignite spontaneously.

Sustained detonations can raise temperatures enough to cause pre-ignition (auto-ignition).

Pre-ignition occurs before normal ignition. Detonation occurs after normal ignition.

Dieseling Engine keeps running after it is switched off Can be caused by: A high idling speed Overheated engine Too many carbon deposits in the chamber Use of a gasoline with an octane rating too low Can be prevented on carburetors Fuel-injected vehicles don’t experience dieseling.

Stoichiometric Ratio (1 of 4)
The chemically correct air–fuel ratio necessary to achieve complete combustion of the fuel and air When oxygen completely combines with the fuel If ratio is stoichiometric, all oxygen and fuel have been chemically combined through complete combustion. Represented by the Greek letter lambda (λ)

Stoichiometric air–fuel ratio for gasoline fuel 14.7 parts air to 1 part fuel, by mass not volume Slightly lean mixture Air–fuel mixture with a higher figure (lambda value of 1.05) has more air in proportion to fuel. Slightly rich mixture Mixture with a lower lambda value (0.95) has proportionately less air than fuel.

Exhaust gas oxygen sensor (lambda sensor) Used to indicate amount of oxygen in exhaust so the PCM can maintain a lambda oscillating just above and below 1. Upstream oxygen sensor Usually installed in the exhaust manifold Measures percentage of oxygen in exhaust gases

Different fuels have a different stoichiometric ratio. Methanol’s air–fuel ratio is 6.4:1 (measured by mass not volume) Ethanol’s air–fuel ratio is 9:1 (measured by mass not volume)

Internal Combustion Requirements (1 of 6)
Air Air is an oxygen-rich combustible gas. Components of air are a mixture of gases and small particles.

Air (cont’d) Four primary components of earth’s atmosphere Nitrogen Oxygen Argon Carbon dioxide

Air (cont’d) Density of air is its mass per unit volume. Density of air in atmosphere changes at different temperatures and altitudes. The amount of oxygen in air directly affects how well it supports combustion.

Fuel Gasoline is fuel for process of internal combustion. Powerful form of energy when mixed with air and pressurized

Pressure Gases exert pressure on all bodies they make contact with. Atmospheric pressure varies with altitude.

Pressure (cont’d) In a gasoline engine position of throttle plate controls volume of air (air–fuel mixture) entering the manifold. A vacuum gauge can be calibrated in inches of mercury in a scale reading from 0″ to 30″. Some engine management systems signal changes in atmospheric pressure by using a barometric pressure sensor in the PCM.

The Carburetor (1 of 9) Carburetor is a supply-and-demand fuel delivery system. Carburetor is usually fed gasoline by an engine-driven mechanical fuel pump. Traditionally, fuel pumps were a diaphragm-type pump driven directly by the camshaft. When engine was running, the pump would draw fuel from the tank and deliver it to the carburetor with low amount of fuel pressure.

The Carburetor (2 of 9) This delivery was then held up at the carburetor’s float bowl that was kept at bay by needle and seat. Delivery into carburetor occurred when the float lowered enough to allow fuel to pass.

The Carburetor (3 of 9) When tuned properly, fuel is delivered effectively. Carburetors were eventually phased out as electronics came into play.

The Carburetor (4 of 9) Circulation system
Fuel is drawn from the tank by a fuel pump. Delivered to solenoid-operated injection valves called injectors Fuel pressure at injector(s) is maintained by a fuel pressure regulator. On most returnless systems, the pressure is controlled by the speed of the pump.

The Carburetor (5 of 9) Fuel filter is directional.
Carburetor supplies the engine with correct air–fuel mixture for all conditions of operation.

The Carburetor (6 of 9) Carburetors come in different designs.
Downdraft design Side-draft carburetors Updraft carburetors

The Carburetor (7 of 9) Each has a float bowl where a float and needle control the fuel level. The air horn and venturi are located in the top of the barrel of the carburetor.

The Carburetor (8 of 9) As piston moves through its intake stroke, it creates a low-pressure area. The venturi is narrower than the rest of the barrel.

The Carburetor (9 of 9) Depressing the accelerator increases air speed through the carburetor. Lowers air pressure at the nozzle Pressure on fuel in the float bowl stays constant. Throttle valve also controls flow of mixture into the engine.

Carburetor Operation (1 of 2)
Delivers correct mixture of air and fuel to each of the cylinders for combustion during the power stroke While engine is running, the intake stroke of each piston creates a low-pressure area (vacuum) in the intake manifold. Vacuum created in a mechanically sound gasoline engine at sea level is between 18″ and 21″ of mercury.

Carburetor Operation (2 of 2)
Differential in pressure allows the clean filtered air to enter the carburetor. Ideally the carburetor precisely governs the air–fuel mixture.

Carburetor Circuits Basic carburetor components are housed inside a metal casting called the carburetor body. Body serves as mounting point for various essential carburetor system components.

Float Circuit (1 of 4) Holds quantity of ready-to-use fuel at atmospheric pressure To allow atmospheric pressure to act on the fuel, the float bowl is open to either: The atmosphere (unbalanced carburetor) The air horn above the venturi (balanced carburetor) Charcoal canister (evaporative emission carburetor)

Float Circuit (2 of 4) If float level is too low:
More airflow through venturi will be required to pull out the fuel, leaning out the air–fuel ratio.

Float Circuit (3 of 4) Float bowl, float, and needle and seat.

Float Circuit (4 of 4) Too high a float level:
Causes the mixture to be too rich. Flooding a carburetor also produces rich mixes.

Idle and Off-Idle Circuits (1 of 2)
When throttle valve is closed or nearly closed: Manifold vacuum created behind throttle is sufficient to pull a small amount of fuel and air through small openings located after the butterfly valve.

Idle and Off-Idle Circuits (2 of 2)

Main Metering Circuit (1 of 4)
As throttle valve opens slightly, the manifold vacuum is reduced. Comes into action above fast idle, as airflow through the venturi increases

A main metering jet in the float bowl meters fuel passing into discharge nozzle.

A main metering jet in the float bowl meters fuel passing into the discharge nozzle.

Throttle opens and airflow increases and speeds up. More fuel is drawn from the discharge nozzle. As throttle opens and engine speed increases, the level in the jet well falls. As throttle opens farther, the fuel level falls. Main metering fuel can typically be adjusted.

Power Circuit (1 of 2) Size of main jet is selected to provide the best mixture for economy under cruising conditions. At low speeds, intake manifold vacuum is transferred through a passage to the vacuum piston. With throttle valve fully open for full engine power, vacuum in the intake manifold falls.

Power Circuit (2 of 2) Some carburetors use metering rods instead of a vacuum piston. Other carburetors use a diaphragm-type power valve.

Accelerator Pump Circuit (1 of 4)
Extra fuel is needed for accelerating. Suddenly opening the throttle increases airflow, but fuel cannot flow from the discharge nozzle quickly enough to match it. Depressing pedal compresses a duration spring that exerts a force on plunger of a small plunger plump.

Fuel flows past a check valve and enters airstream from a discharge nozzle above the venturi.

The duration spring extends the time for delivering the fuel. The check valve closes and the inlet valve opens to let fuel refill the pump chamber from the float bowl.

The Choke (1 of 3) Fuel ignites less readily when cold.
To compensate, the choke restricts flow of air at the entrance to the air horn.

The Choke (2 of 3) The choke can be controlled manually by a cable that operates the valve. The choke should operate as briefly as possible.

The Choke (3 of 3) The choke.

Carburetor Barrels (1 of 6)
Carburetors can have one, two, three, or four barrels. Two-barrel carburetors Have two outlets to the intake manifold Leaves the float chamber unaffected by cornering, climbing, accelerating, or braking

Progressive carburetor Throttles open in two stages. Combines the two barrels to act as a single carburetor

Progressive carburetor (cont’d) One of two barrels of the carburetor has all the circuits needed to supply mixtures for the whole range of operation. The other barrel supplies extra mixture but only at high speed or full throttle.

Engine starting Throttle on the secondary side is already closed. From idle to medium speeds only the primary throttle is open. Secondary throttle opens to admit more air–fuel mixture when engine speed rises to where additional breathing capacity is needed.

Engine starting (cont’d) By the time the primary throttle is wide open, so is the secondary throttle. The opening of the throttles can be controlled mechanically or by vacuum unit. When air flows past ports in the venturis, it produces low-pressure areas.

Large-capacity V8 engines may use a four-barrel carburetor of two-stage design. Effectively two, two-stage carburetors are combined. A central molded plastic fuel bowl and suspended metering system can be incorporated into the design.

Computer-Controlled Carburetors (1 of 3)
Normally use an electronically controlled solenoid valve to respond to the PCM commands

A computer-controlled carburetor normally uses an electronically controlled solenoid valve.

Use various sensors in the exhaust and engine to monitor operating conditions Send that information to the PCM The PCM calculates rich or lean fuel condition. Computer constantly sends commands to the mixture-control solenoid to open and close air and fuel passages in the carburetor.

Mechanical Fuel Pump (1 of 4)
Usually mounted on the cylinder head or the engine block Has a flexible diaphragm that is a flexible piece of neoprene rubber separating two chambers

The mechanical fuel pump has a flexible diaphragm—a flexible piece of neoprene rubber separating two chambers.

Diaphragm is operated by an eccentric on the camshaft. Eccentric rotates, making the rocker arm move. Movement is transferred to the diaphragm, pulling it down. Fuel is drawn into the pumping chamber on the other side of the diaphragm. Diaphragm spring moves diaphragm up forcing fuel from pumping chamber out of the pump into the carburetor.

When the engine needs more fuel: Diaphragm moves through a long stroke to pump a lot of fuel. When less fuel is needed: Pressure builds up in the fuel line to the carburetor and in the pumping chamber. Some pumps have a return line. As fuel circulates, it cools the fuel pump and lines, reducing the chance of vapor locks.

Electric Fuel Pump (1 of 3)
Diaphragm pump Has an electrical section and a mechanical section When the ignition is switched on, current magnetizes the solenoid.

Diaphragm-type electric fuel pump.

Diaphragm pump The magnetic field energizes an armature. Pulling down the diaphragm breaks the circuit and stops the current. The armature is released and the diaphragm spring forces up the diaphragm. When the engine needs less fuel Some have a safety switch that prevents the pump from continuing to run if the engine stops.

Fuel Tank (1 of 5) The primary reservoir of the on-board fuel supply

Fuel Tank (2 of 5) The typical fuel tank of modern vehicles consists of a gas cap, filler neck, fuel, fuel pump, and gauge sending unit.

Fuel Tank (3 of 5) Fuel tank of modern vehicle consists of: Gas cap
Filler neck Fuel Fuel pump Gauge sending unit

Fuel Tank (4 of 5) Primary function
Safely holds an adequate supply of gasoline Where tank is mounted depends where the engine is and on space and styling. Tanks are made of tinned sheet steel that has been pressed into shape or nonmetallic materials.

Fuel Tank (5 of 5) Fuel expands and contracts as temperature rises and falls. Fuel tanks are vented to let them breathe. Modern emission controls prevent tanks from venting directly into the atmosphere. Liquid fuel closes check valve and blocks line. Stops it from reaching the charcoal Some systems have a small container called a liquid-vapor separator above the fuel tank.

Fuel Filler Neck (1 of 2) Fuel filler is where fuel enters the tank.
Fuel filler neck is a pipe that extends above the fuel tank. Its diameter is smaller than those on leaded vehicles.

Fuel Filler Neck (2 of 2) Location depends on design of the vehicle and location of the tank. The filler neck can incorporate the use of a blowback ball valve.

Gas Cap (1 of 2) The EPA requires modern vehicles to have a nonvented gas cap. Prevents fuel vapors from directly venting to the atmosphere Many caps use a ratchet system to ensure that the cap is tightened properly.

Gas Cap (2 of 2) Newer Ford vehicles are using an Easy Fuel capless system.

Fuel Pump Relay (1 of 2) Relay is an electromagnetically operated switch. Activates fuel pump when ignition is turned on for priming the fuel system Low-amperage current is passed through the winding in the relay. A magnetic field is created that pulls the contact together. Controlling the larger current flow going to the fuel pump

Fuel Pump Relay (2 of 2) The current operating the fuel pump relay winding is typically controlled by the PCM. PCM grounds the winding when it wants the fuel pump to operate.

Fuel Pump (1 of 5) Most fuel-injected vehicles use one or two electrical pumps. Pumps supply the fuel system with pressurized fuel. Pump is mounted on either the frame or located inside the fuel tank. If in the tank, it is a submersible pump. Electric fuel pumps can be low-pressure or high-pressure.

Fuel Pump (2 of 5) Electrically operated and electronically controlled
Driven by a permanent magnet electric motor

Fuel Pump (3 of 5) Fuel flows through the pump and around the electric motor when it is running. There is never an ignitable mixture (of air and fuel).

Fuel Pump (4 of 5) Designed to deliver more fuel than the maximum requirement of the engine Pressure in the fuel system is maintained at all times.

Fuel Pump (5 of 5) Electric fuel pumps use various types of pump chambers. The roller cell Rollers float in the channels in an offset rotor. Other types Peripheral Side channel pump

Fuel Tank Sending Unit (1 of 2)
Primary job of the sending unit Send constant electrical signals to gas gauge or to the BCM, which then controls gas gauge A variable resistor attached to a float mechanism

Fuel Tank Sending Unit (2 of 2)
On today’s EFI vehicles, the sending unit is incorporated with the fuel pump. The entire assembly has three jobs. Pick up fuel from the bottom of the tank by way of the fuel pump Strain (filter/clean) the fuel and pressurize it Report level of fuel in the tank to the driver information center These systems are meant to last at least the life of the warranty.

Filter Sock The first line of defense for fuel contamination
Incorporated into the end of the fuel pickup tube Typically consists of a fine mesh

Fuel Lines (1 of 2) Usually made of metal tubing or synthetic materials A fuel supply line carries fuel from the tank to the engine. A return line may also be provided.

Fuel Lines (2 of 2) Evaporative emission system lines run along with the fuel lines. Connect between the fuel tank, charcoal canister, and intake manifold Can be damaged by rust or foreign objects or lifting a vehicle improperly

Fuel Rail (1 of 3) A special manifold designed to provide a reservoir of pressurized fuel for fuel injectors Can also serve as a mounting place for the fuel pressure regulator

Fuel Rail (2 of 3) The couplings where the fuel lines meet the fuel rail are usually sealed by: Flared ends Quick-connect high-pressure O-rings Banjo fittings

Fuel Rail (3 of 3) Schrader valve
Provides a means for connecting a fuel pressure tester to the rail Uses a one-way valve to hold pressure in the system while pressure tester is connected and disconnected to the fuel rail Usually covered by a screw-on cap with a seal inside to prevent leaks

Fuel Pressure Regulator (1 of 5)
Fuel pressure must be regulated. On port fuel-injected engines, fuel pressure needs to be maintained above manifold pressure. Manifold pressure changes with engine load, and fuel pressure also needs to change with it.

Some vehicles use a pressure regulator.

The fuel pressure regulator mounted on the fuel rail incorporates a diaphragm-operated valve. A pressure spring and engine vacuum are on one side of the valve. On the other side is fuel pressure from the fuel pump.

Movement of the diaphragm opens and closes the valve. Vents pressure to fuel tank through return line Fuel pressure builds against the diaphragm. Once it hits preset pressure, valve will open slightly and bleed off pressure. Reduces the pressure on the diaphragm, closing the valve With the valve closed, the pressure rises again, until the valve once again opens.

Fuel pressure regulator doesn’t adjust the pressure when the engine load is increased. Spring-loaded vacuum chamber is connected by a manifold vacuum line to intake manifold. The vacuum pulls against spring pressure to modify the pressure at which the valve opens. As the driver accelerates, the manifold vacuum diminishes.

Fuel Injector (1 of 5) The modern fuel injector is a spring-loaded, electric-solenoid spray nozzle.

Fuel Injector (2 of 5) The nozzle can be of several types.
Rotating disc style Pintle style Ball-valve style

Fuel Injector (3 of 5) Sprays the proper amount of gasoline in the proper pattern Into the intake ports Directly into the combustion chamber Into a prechamber in response to signals from the PCM Positioned between the fuel rail and the intake manifold

Fuel Injector (4 of 5) When the SCM sends an electric signal to the fuel injector: Injector opens for a specified time. Current is stopped and an internal spring returns the injector to the closed position. It waits for the next “on” command. Happens repeatedly hundreds of times per minute at each fuel injector

Fuel Injector (5 of 5) The fuel injectors are designed and built to very exacting tolerances. Response time to lift injector needle to the fully open position is about 1 millisecond. If battery voltage is low, response time takes longer. The engine receives less fuel. The PCM can compensate for this delay.

Types of EFI Systems (1 of 3)
There are three basic EFI systems.

A. Throttle body injection. B. Multipoint fuel injection. C. Direct injection.

They all operate on similar principles. Fuel is supplied to injectors at specified pressure. PCM sends electric signal to each injector to cause it to open for a certain amount of time. Fuel is injected into intake manifold or combustion chamber.

Throttle Body Injection (TBI) System (1 of 2)
Also known as single point injection or central-point injection A system with one or two fuel injectors Located centrally on the intake manifold right above the throttle places Fuel is sprayed into the top center of the throttle body. Then atomized with the incoming filtered air

Throttle Body Injection (TBI) System (2 of 2)
TBI is a simpler system. Requires only one or two injectors PCM can be of simpler, less powerful design. Since fuel is sprayed above throttle plates, it is at atmospheric pressure. Pressure drop across the injector is the same Fuel pressure does not need to change with throttle opening or engine load. The central injector is normally triggered on every ignition pulse.

Multipoint Fuel Injection (MPFI) System (1 of 9)
A fuel injector is used for each cylinder. Injector is located in the intake manifold near each intake valve. Each injector also has an electrical connector that provides it with power and ground.

Most electronic fuel injectors are supplied with constant battery voltage. The PCM then switches the negative side of the injector circuit to ground to turn it on. When the PCM switches the negative side of the circuit off: The spring in the injector closes the injector and fuel stops spraying.

Return-style MPFI systems Fuel pressure regulator inlet is connected to the fuel rail. An outlet lets fuel return to the tank. A control diaphragm and pressure spring determine the exposed opening of the outlet and the amount of fuel that can return.

Return-style MPFI systems (cont’d) The strength of the pressure spring determines fuel pressure in the fuel rail and keeps it at a fixed value. The pressure in the intake manifold varies considerably with changes in the engine speed and with load.

For any injection duration, if fuel is held at constant pressure: As manifold pressure varies, so does the amount of fuel delivered. Fuel pressure must be held constant above manifold pressure. Pressure is held by sealing the spring housing of the pressure regulator. When manifold pressure changes, so does the fuel pressure.

When manifold pressure is low: Fuel pressure is low. As manifold pressure rises toward open throttle: Fuel pressure rises. Since injectors are all subjected to the same pressure, they all inject equal amount of fuel.

Manifold pressure sensing is not required in TBI systems. Injection occurs above the throttle plate, at atmospheric pressure. Injectors are sealed into the manifold by O-rings.

For a short time after an engine is switched off, the engine temperature keeps rising. Can produce vapor in the fuel lines Check valve in the pump maintains fuel pressure.

The circulation of fuel ensures that cool fuel is delivered at all times and vapor formation is prevented. While the engine is running Pump control circuit allows the pump to operate for a few seconds when ignition is switched.

Gasoline Direct Injection Systems (1 of 3)
The successor to indirect fuel injection Sprays fuel directly into the cylinder Fuel injector of each cylinder is located in the cylinder head.

Fuel is directly sprayed into combustion chamber as an atomized mist. At the precise time it is needed

Stratified charge Engine can run so lean because injector can place fuel in a localized spot. Use of spark plugs Provides computer with more choices about when fuel gets injected GDI fuel systems can be of either a low-pressure variety or a high-pressure variety.

Returnless Fuel Injection Systems (1 of 4)
Used to reduce evaporative emissions The fuel returning to the tank is hot from engine heat on a return system. No hot fuel is returned to the tank in a returnless system. The fuel in the tank stays relatively cool.

Two types of returnless systems Mechanical Uses a pressure regulator in the fuel tank Electronic Controls speed of fuel pump to modify pressure

Mechanically controlled system Uses a spring-loaded pressure regulator Does not change with manifold pressure and therefore does not use a vacuum hose Excess fuel pressure is vented into the tank.

Electronically controlled system The PCM sends a square wave (digital) signal. The faster it turns, the higher the pressure and flow. The slower it turns, the lower the pressure and flow. The PCM monitors fuel pressure through a fuel pressure sensor. Mounted on the fuel rail Controls fuel pump based on engine speed, load, and other factors

Simultaneous Fuel Injection
Triggered at the same time or in groups Injectors operate twice per cycle. Triggered every third ignition pulse Actual operating time of the injectors depends on battery voltage.

Sequential Fuel Injection (1 of 2)
Injection occurs in the sequence of firing order. Follow the firing order of the engine. Each injector opens only once in each cycle to deliver the fuel needed. PCM needs individual drivers to turn each injector on and off because each injector is controlled separately.

Sequential Fuel Injection (2 of 2)
This system requires more computing power to manage each injector circuit. The timing of the injection pulse is important. Each injector only fires once per cycle. Added load placed on the engine during idle can be compensated for. The extra mixture delivered increases engine torque and maintains idle speed.

Air Supply (1 of 3) Air required for combustion of fuel is led from air filter through the throttle valve and into common manifold (plenum chamber).

Air Supply (2 of 3) From here individual intake runners, or pipes, branch off to each cylinder. Design of the intake system determines how large an air mass can be drawn into a cylinder at any given engine rpm.

Air Supply (3 of 3) With unobstructed passages to each cylinder, the cylinder fills with air as efficiently as possible. The temperature of the air influences how dense the air–fuel mixture will be. Cold air is denser than hot air so it has a greater mass in any given volume.

Air Measurement (1 of 6) The amount of air entering the engine must be measured or calculated. The volume of air can be determined in two ways. Speed density calculation Direct measurement

Air Measurement (2 of 6) The volume of air entering the engine varies.
According to the engine speed and the load If calculations are used, they are based on: Engine rpm As measured by the manifold absolute pressure sensor Engine load

Air Measurement (3 of 6) Airflow can be calculated using preprogrammed fuel maps. The oxygen sensor provides feedback about the richness or leanness of the fuel injected. A mass airflow (MAF) sensor directly measures mass of filtered air entering the engine. The Karman vortex airflow sensor measures airflow disruptions.

Air Measurement (4 of 6) There are three types of vortex sensors.
All use an air regulator to smooth out or reduce turbulence in the airflow entering the sensor. A triangular vortex column disrupts a portion of airflow, creating vortices or whirlpools in the airflow.

Air Measurement (5 of 6) “Whirlpoools” are measured by: Optical type
Ultrasonic type Pressure type

Air Measurement (6 of 6) Regardless of the method used to measure the whirlpools, all sensor types produce a 5-volt digital signal with a frequency that is proportional to the airflow through the sensor.

Fuel Shutoff Mode (1 of 2) Exists in case the vehicle suffers a collision or rollover accident. Vehicle uses various accelerometers to monitor key indicators of an accident requiring fuel shutoff.

Fuel Shutoff Mode (2 of 2) Most vehicles with a fuel shutoff system have specific reset procedures. The inertia switch.

Efficient Combustion (1 of 10)
For efficient operation of the catalytic converter. Mixture ratio must be maintained close to stoichiometric ratio. Efficiency can be monitored by measuring the percentage of oxygen in exhaust gas. Oxygen sensor tells the PCM how much oxygen is in the exhaust gas.

Adaptive learning Feedback allows fuel settings to change as components age. PCM memorizes fuel settings for different operating conditions and stores for future use. If fault occurs, a fault code will be memorized. Can be retrieved by connecting a scan tool to the data link connector Information on the fault can then be analyzed.

Most injectors operate at the nominal battery voltage of 12 volts. But many sensors have reference voltage of 5 volts. Adjustment is made by a voltage regulator.

During engine operation, there are three main pollutants created. Nitrogen oxides Carbon monoxide Hydrocarbons These enter the catalytic converter. Efficiency of conversion depends on composition of the exhaust gases, which depends on air–fuel mixture.

If air–fuel ratio supplied to the engine is too rich: Nitrogen oxides are converted efficiently but carbon monoxide and hydrocarbons are not.

Highly efficient conversions of all three occur in a narrow range of air–fuel ratios. Vehicles with a three-way catalytic converter have a feedback system called looping. The stoichiometric point.

Closed loop Control unit receives feedback from oxygen sensor and acts to alter the injection setting.

Open loop Feedback to the control unit is ignored. Settings are determined from programmed memory. When the oxygen sensor reaches its operating temperature (around 600°): Sends an output voltage to control unit to signal whether mixture is richer or leaner than lambda.

When mixture deviates from this point, output voltage changes sharply above or below its switching point (approximately 0.45 volts).

Voltage of the signal from oxygen sensor changes sharply when air–fuel mixture changes from lean to rich. Control unit adjusts pulse width of the injector accordingly to ensure the most efficient operation of the catalytic converter.

Short- and Long-Term Fuel Trim (1 of 3)
The oxygen sensor is the computer’s window into the exhaust stream. Used to validate the accuracy of the computer’s pulse width signal Richening and leaning is called short-term fuel trim (STFT).

PCM watches average of richening and leaning over short periods of time. PCM aims to keep the STFT at its midpoint so it can respond to any needed changes. If sees STFT creeping away from the midpoint, PCM will increase or decrease its base pulse-width setting and bring the STFT back to center. Will then record that base adjustment as long-term fuel trim (LIFT) percentage

STFT and LTFT are useful when diagnosing drivability concerns.

Fuel Pump Relay (1 of 2) Most fuel pumps are operated by a fuel pump relay. Relay controls power to the fuel pump.

Fuel Pump Relay (2 of 2) Typically controlled by the PCM
Electrical pump will continue running as long as electricity is flowing to it. For safety, PCM will shut down fuel pump relay if it does not see from crankshaft position sensor that engine is running above about 350 rpm. Some vehicles use an inertia switch to turn the fuel pump off in the event of an accident

Digital Versus Analog Signals (1 of 2)
Produces a signal that is smooth and gradually changing in strength Digital signal A direct on/off with no in-between transition

Digital Versus Analog Signals (2 of 2)
Analog signals lack true reaction timing of the new age of digital signal.

Frequency (1 of 2) Sound travels through the air by producing pressure waves. The rate at which these waves reach our ears is called frequency. Measured in cycles per second Cycle is distance between waves or wavelength.

Frequency (2 of 2) The higher the frequency, the higher the pitch of the sound. An engine produces sound across a wide range of frequencies. Mufflers and resonators in the engine exhaust system reduce these sounds to an acceptable level.

Potentiometer (1 of 2) A mechanically variable resistor
Normally a film type in EFI applications Can be linear or circular in construction Has three electrical connecting points A reference voltage is applied to the resistor so a steady current flows through it.

Potentiometer (2 of 2) In automotive applications, the circular form is commonly used as a throttle position sensor. Center contact is attached to the throttle plate. Throttle plate position can be monitored by the control unit.

Thermistors (1 of 2) A resistor that changes its resistance with the changes in temperature Used in various temperature-related controls Coolant temperature sensors Fuel temperature sensors Ambient temperature sensors

Thermistors (2 of 2) The cabin temperature sensor’s internal resistance may decrease when the cabin temperature increases. The resistance change causes a change in a voltage signal. The system can maintain a driver-selected temperature.

Crankshaft Position Sensor
Sends information on speed and position of the crankshaft to the PCM For control of ignition timing and injection sequencing Control unit can trigger ignition and injection to suit virtually all operating conditions. The crankshaft position (CKP) sensor may be mounted externally on the crankshaft housing.

Inductive-Type Sensors (1 of 7)
Sense movement of the ring gear teeth on the flywheel, or a toothed disc on crank pulley The sensor is mounted on crankcase housing. Stator is positioned so it has a very small clearance, or air gap, between end of the soft iron core and the flywheel teeth.

As flywheel rotates, teeth approach and leave the stator. Air gap changes. Strength of the magnetic field changes. The winding is part of a complete circuit. As tooth moves away from stator, the strength of magnetic field changes again.

Polarity changes every time a tooth approaches and leaves the stator. As the tooth approaches the stator, the magnetic field changes.

Crankshaft position is detected by a separate sensor that is also an inductive type. Ignition timing is decided according to operating conditions and is triggered to occur a certain number of degrees from that point.

Hall-effect CPK sensor Measures engine speed Represented in rpm of the crankshaft Metal disc attached to the crankshaft or camshaft is very close to the sensor. Around the circumference of the disc there are evenly spaced teeth or cogs.

The sensor is stationary. Usually located in the engine block with an O-ring to seal in engine oil Contains a magnetic coil that reacts with the magnetic field as each cog passes by the tip of the sensor

When the crankshaft spins, induction current is set up around the magnetic coil. The cog edge of the crankshaft obstructs the sensor’s magnetic field, creating a signal.

Ignition Pickup Style Position Sensor
Primarily a Ford design Known as profile ignition pickup (PIP) A Hall-effect van switch Provides crankshaft position data to the Ford ECC-IV processor Allows system to make adjustments to the fuel injection according to driver requirements

Camshaft Position Sensor (Cam Sensor)
Sends constant data to the computer Constantly reads a magnetic point on the camshaft or distributor housing CMP sensor works in conjunction with a knock sensor and the computer. Keeps ignition timing adjusted for all load conditions Reducing the pinging and knocking

Throttle Position Sensor (1 of 4)
Gathers information on throttle position Allows the control unit to make adjustments according to operating conditions Located on the throttle body

Operated by rotation of the throttle shaft A potentiometer-type sensor monitors throttle position over its full range. One side has 5-volt reference voltage from the control unit. Other side connects to the control unit ground. Third wire runs from a sliding contact in the TPS sensor to the input circuits of the control unit.

The sensor works like a variable resistor. At closed throttle: The reading is usually below 1 volt. As the throttle valve opens: The voltage signal rises. At wide-open throttle: It is about 4.5 volts.

Ongoing monitoring provides accurate data for the control unit. Allows control over a wider range of operating conditions

Engine Temperature Sensors (1 of 3)
Coolant temperature sensor (CTS) Immersed in coolant in cylinder head, block, or intake manifold Consists of hollow threaded pin that has a resistor sealed inside Signal from CTS is used by PCM to control the mixture throughout its operating temperature. Enrichment occurs during engine cranking. Control unit continually monitors coolant temperature during engine operation.

Sometimes a cylinder head temperature sensor is used instead of a CTS to signal engine temperature. Air temperature needs to be monitored by PCM.

Intake air temperature (IAT) sensor Installed in the airflow sensor Positioned in the airstream Manifold air temperature (MAT) sensor Installed in the intake manifold Located in one of the intake runners Both IAT and MAT relay information on air temperature and the density of the air.

Oxygen Sensor (Before and After Catalytic Converter) (1 of 5)
Positioned in the exhaust pipe Provides engine management PCM with an electrical signal that relates to amount of oxygen in the exhaust gas Old oxygen sensors were stoichiometric sensors.

“Nernst cell” Inside the sensor Operates by comparing amount of oxygen in the exhaust gas to oxygen levels in the outside air The Nernst cell needs to be hot.

Broad-band oxygen sensor (wide-band oxygen sensor) Informs PCM of a range of air-fuel ratios from 9:1 to atmospheric air Ideal for optimum emissions where incoming air is unthrottled Not restricted by throttle butterfly lean-running GDI engine Nernst cell is still used.

Broad-band oxygen sensor (wide-band oxygen sensor) (cont’d) Current through heat is controlled by the PCM. A minute chamber within sensor has access to the exhaust gas. Computer controls current flowing through pump. One flows one direction through the pump, adds oxygen. Other flows opposite direction, removes oxygen.

Since 1996 nearly all manufacturers install an oxygen sensor before and after the catalytic converter. Test for correct operation. Catalytic converter needs to store and release oxygen from catalyst to change exhaust gases correctly.

Manifold Absolute Pressure (MAP) Sensor (1 of 3)
Measures pressure changes in engine speed and load Converts them into electrical signal The PCM senses manifold pressure by monitoring output signals. MAP sensor can use a piezoelectric crystal.

Exhaust gas recirculation (EGR) valve A MAP sensor is used. Monitors changes in manifold pressure when determining if the EGR valve is open or not Sensor is connected to intake manifold by a small-diameter, flexible tube. Control unit typically sends a 5-volt reference signal to the sensor.

As manifold pressure changes, so does the electrical resistance of the sensor. Manifold pressure is low (high vacuum) during idling. Manifold pressure is higher and closer to atmospheric pressure (low vacuum) during wide-open throttle.

Barometric Pressure (BARO) Sensor
Measures barometric pressure Helps calibrate the fuel injection system BARO sensor works with the MAP sensor. Older BARO sensors were typically mounted on firewall or along the engine bay. Late-model vehicles use MAP sensor to take a barometric pressure reading before vehicle is started.

Air-Conditioning Compressor Clutch Signal
Air conditioner creates a load on the engine when it is on. Load drags the engine down. PCM counteracts load by sending a command to engine idle speed controller to open slightly.

Knock Sensor (1 of 8) Engine knock occurs in the combustion chamber.
There is an unwanted spike in pressure caused by pre-ignition or detonation. Some vehicles have a knock sensor. Monitors noise created by the pressure spike

Knock Sensor (2 of 8) Knock can be created by:
Excessive load on the engine Ignition timing that is too advanced Overheating of the engine PCM can adjust the ignition timing to help reduce knocking.

Knock Sensor (3 of 8) Excessive load on the engine Ignition starts.
The expanding gases create a pressure wave designed to push the piston down. The forces opposing piston movement are too high. The piston accelerates slowly and maintains a small volume above the piston.

Knock Sensor (4 of 8) Excessive load on the engine (cont’d)
The unburnt mixture is compressed by the advancing pressure wave. This fuel self-ignites due to an increase in temperature and creates its own flame front. The two advancing flame fronts create a huge spike in pressure. This knock has enough energy to badly damage pistons, rings, spark plugs, and rod bearings.

Knock Sensor (5 of 8) Overheated engine—faulty thermostat
Ignition starts. Expanding gases create a pressure wave designed to push the piston down. Temperature of the unburnt fuel is too high due to the overheated engine.

Knock Sensor (6 of 8) Overheated engine—faulty thermostat (cont’d)
Unburnt mixture is compressed by the advancing pressure wave. Fuel self-ignites due to increase in pressure/temperature and creates its own flame front. The two advancing flame fronts create a huge spike in pressure, creating engine knock. Fuel igniting later in compression stroke can overcome engine knock.

Knock Sensor (7 of 8) The knock sensor
Produces electrical signal that PCM can use to determine if knock has occurred The PCM will retard timing a few degrees and listen to detect if knock is still present. If still present, PCM will continue to retard timing in steps until knock is eliminated. If knock is not occurring, PCM will advance timing a degree or two and listen for knock.

Knock Sensor (8 of 8) The sensor cannot always know the difference between knock and a loose air-conditioning compressor bracket rattling. V-configured engines often have two knock sensors installed.

Vehicle Speed Sensor (VSS)
A detection device that sends vehicle speed information to the ECM Located In the instrument cluster Mounted on the transmission or transfer case

Inertia Sensors (1 of 2) System using inertia sensors has fuel pump.
Will only operate when the safety circuit containing the inertia sensor is complete In this circuit there is a fuel cutoff switch. Used if vehicle is involved in a serious accident

Inertia Sensors (2 of 2) Sensor consists of a steel ball held in a funnel-shaped container by a magnet. Steel ball breaks free from magnet’s restraining force. 214

Fuel Pressure Sensor Mounted on the fuel rail
Allows PCM to monitor fuel pressure in the fuel rail It can control the speed of the fuel pump to maintain the correct pressure in the system.

Misfire Monitoring (1 of 2)
Misfire can cause catalytic converters to overheat in a short time. A steady misfire occurs due to an ignition problem.

Misfire Monitoring (2 of 2)
Detecting the misfire If PCM detects a steady misfire, it will cause MIL to blink (not just come on steady). Monitoring software identifies unacceptable changes in crankshaft speed. Information allows PCM to store a cylinder-specific misfire code or a random misfire code.

Output Signals Signals the computer sends to motors and actuators to do work Output signal is sent to the corresponding “worker” when a specific criterion is met or the driver gives a certain command.

Relays Used as an actuator when computer controls a high-current load
Computer controls the relay ground circuit. When high-current job is requested, computer completes the ground circuit. The relay coil field pulls mechanical contacts closed.

Ignition Control Module (ICM) (1 of 2)
Controls ignition hopefully for the life of the vehicle The ICM receives signals or inputs from: CMP sensor CKP sensor PCM

Ignition Control Module (ICM) (2 of 2)
Inputs are correlated to an exact firing moment for each spark plug at each cylinder at extremely high voltages. Timing is varied because of varying conditions or engine loads. Location depends on design and space. Mounted on or around the ignition coils on a direct injection system On/in the distributor

Idle Speed Control Devices (1 of 4)
Solenoid-type air control valve Acts on signals from control unit to bypass a measured airflow around the throttle plate Position of the valve Depends on how much current the control unit applies to the solenoid Maximum current flow opens the valve fully to give maximum airflow.

Duty cycle Amount of valve opening and airflow depends on the on time of the pulse. A long on pulse with a short off pulse produces: A high average voltage A large opening of the valve A short on pulse with a long off pulse produces: A low average voltage A small opening of the valve Increase in airflow

Duty cycle (cont’d) Generally expressed as a percentage A variation in pulse width at the set frequency is called pulse-width modulation. The stepper motor type of idle control Tapered pintle is positioned using a screw and nut assembly.

Solenoid valves can also be used to bypass a predetermined amount of air around the throttle place. These may come into operation for specific load compensation.

Electronically Controlled Throttle (1 of 3)
Commonly referred to as drive-by-wire or throttle-by-wire Replacement device for the long-standing standard of the throttle cable Uses a pedal position sensor to calculate desired throttle position of the driver

Command is sent to the PCM. PCM sends a command to a throttle servomotor to open or close throttle butterflies. The computer can regulate: Cruise consistency Acceleration Deceleration

Improves fuel economy, reduces emissions and prevents sudden changes in speed that could affect life of drive train components Some late-model high-end vehicles may have a throttle response choice of “touring” and “sport.”

Replacing a Fuel Filter (1 of 6)
Replaced according to manufacturer’s specified replacement schedule Or if restricted flow is encountered Fuel filters can be located: Under hood in the engine compartment Inside fuel tank as part of fuel pump assembly

Bleed the pressure off before opening the system. Remove fuel pump relay or the fuel pump fuse. Connect a fuel pump gauge that has a bleed valve to the fuel rail test point. Vent pressure in gas tank by removing the cap.

Some vehicles use metal or plastic lines that bolt onto the filter using a flared fitting or banjo bolt. For either, you will need to use double wrench method to unbolt the line. Newer vehicles use quick couplers to retain fuel lines on the fuel filter. Couplers make it quick and easy for the factory to install the filter.

Flexible fuel lines connect fuel tank to the filter. Check condition to determine if you need to replace hoses and clamps when replacing the filter. Some replacement filters come with hoses and clamps.

Types of clamps for flexible fuel lines Spring type Worm type Rolled edge Use the appropriate tool when installing new clamps on the hoses.

Sometimes fuel filters are installed in the fuel tank along with the fuel pump assembly. Get to the pump and filter through the top of the fuel tank. Manufacturers may provide a removable access cover under the backseat. Tanks could need to be removed to gain access.

Inspecting and Testing Fuel Pumps (1 of 5)
Need to be tested if a vehicle experiences low engine power or the vehicle will not start due to a fuel-related issue Some shops test to see if it is nearing failure.

Pressure/volume test Measures the fuel pressure being delivered and the volume of the fuel pump Many fuel-injected vehicles provide a test port. Pressure can be measured with the key on or with the engine running.

Pressure/volume test (cont’d) Compare to pressure specifications provided by the manufacturer. Pressure may be within specifications and hold pressure when the engine is off, but fuel pump volume may be low. Most EFI fuel pressure gauges have a valve that allows fuel to be taken from the rail without killing the engine and then caught in a calibrated container.

Lab scope inductive current flow test As each pair of segments of fuel pump’s commutator aligns with brushes, current flows through connected windings in the armature.

Scan tool data stream test Set scan tool to record: Rpm VSS Front oxygen sensors Short-term fuel trim Long-term fuel trim Go on a test-drive. Check the recording.

Checking Fuel for Contaminants and Quality (1 of 3)
Fuel can cause drivability issues. If it becomes contaminated or old, or if it is the wrong fuel All tests require getting a sample from the fuel supply. Best taken from fuel rail or where gas enters the carburetor

Visual testing Collect a cup or two of fuel in a clear container. Allow fuel to settle and look at it.

Alcohol content test A mixture of 10 mL of clean water and 90 mL of gasoline are carefully agitated for 30 seconds. Allow the mixture to settle for a minute or two. Each mL above 10 equals percentage of alcohol in the gasoline. Most vehicles can tolerate 10% alcohol. Flex fuel vehicles can typically operate on 85% alcohol.

Inspecting and Testing Fuel Injectors (1 of 3)
Can fail electrically or mechanically If injectors fail completely, cylinder will misfire. Injectors have a poor spray pattern due to deposits. Identify injector that is causing a drivability issue before specifically testing it.

Use diagnostic skills and tools to narrow down the fault to the injectors. Pressure drop test Perform if the injector resistance and on/off signal are good. Checks if the injector is restricted with deposits. Uses a fuel pressure gauge and injector pulsing tool Pressurize fuel rail by turning key to on position and charging the fuel rail.

To inspect and test fuel injectors: Research fuel injector testing procedure and specifications. Inspect fuel injectors for leaks and damage. Follow the service information to test.

Summary (1 of 11) The most important job of the fuel system is optimizing engine performance while keeping fuel consumption and emissions to a minimum. As a technician you must be able to properly inspect, diagnose, and repair fuel system components for your customers, thus keeping their vehicles running at optimum efficiency and performance.

Summary (2 of 11) Modern fuel injection has three subsystems: fuel supply, air supply, and fuel metering. Vapor lock occurs when vapor forms in the fuel line; the bubbles of vapor block the flow of fuel at the pump and stop the engine. Engines perform best when used with the fuel that has the engine manufacturer’s recommended octane rating.

Summary (3 of 11) Combustion is the burning of the air–fuel mixture.
Detonation is when the entire mixture explodes instead of burning smoothly across the combustion chamber. Gasoline must be burnt in a controlled manner or it will burn either too fast or too slow.

Summary (4 of 11) The term stoichiometric ratio describes the chemically correct air–fuel ratio necessary to achieve complete combustion of the fuel and oxygen in the air. Air is one of the essential components of the internal combustion engine. Fuel pumps can be electrical or mechanical. The most common today are electrical and are installed in the fuel tanks.

Summary (5 of 11) Most of today’s vehicles use electronic fuel injection (EFI), which is better for fuel economy and emission controls. The typical fuel tank (or gas tank, as it is sometimes called) of modern vehicles consists of a gas cap, filler neck, fuel, fuel pump, and gauge sending unit. The tank’s primary function is to hold an adequate supply of fuel.

Summary (6 of 11) Modern vehicles are required by the Environmental Protection Agency (EPA) to have a nonvented gas cap. This nonvented cap prevents the dangerous fuel vapors from being directly vented to the atmosphere. There are three types of electronic fuel injection—throttle body injection (TBI), port fuel injection (PFI), and gas direct injection (GDI).

Summary (7 of 11) Airflow and volume are critical in ensuring the engine has the correct ratio of air to fuel. All electronic fuel systems use sensors and other devices to tell the PCM how much fuel is needed for a given engine operating condition.

Summary (8 of 11) The crankshaft position (CKP) sensor uses information on the speed and position of the crankshaft to control ignition timing and injection sequencing. The camshaft position (CMP) sensor sends constant data to the computer to let it know which cylinder is on its power stroke as well as the position of the camshaft and valve.

Summary (9 of 11) The throttle position sensor (TPS) gathers information on throttle positions to allow the control unit to make adjustments according to operating conditions. Engine coolant temperature maintains the air–fuel ratio within an optimum range. The control unit must take account of coolant temperature and air temperature.

Summary (10 of 11) Manifold absolute pressure (MAP) measures changes in engine speed and load and converts the findings into an electrical signal to control engine operations. The vehicle speed sensor (VSS) is a detection device that sends the vehicle speed information (i.e., how fast the vehicle is traveling) to the electronic control module.

Summary (11 of 11) If the fuel system is maintained, it will give many years of dependable service to the vehicle’s owner. Always refer to the manufacturer’s technical data for the latest service information on the specific vehicle that is being serviced or repaired.

Credits Unless otherwise indicated, all photographs and illustrations are under copyright of Jones & Bartlett Learning.

CHAPTER 48 Gasoline Fuel Systems.

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CHAPTER 48 Gasoline Fuel Systems.

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Presentation on theme: "CHAPTER 48 Gasoline Fuel Systems."— Presentation transcript:

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