Halderman ch078 lecture

FUEL-INJECTION COMPONENTS AND OPERATION 78

Objectives The student should be able to: Prepare for ASE Engine Performance (A8) certification test content area “C” (Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair). Describe how a port fuel-injection system works. Describe the fuel injection modes of operation.

Objectives The student should be able to: Discuss central port injection (CPI) systems. Explain how a stepper motor works. Discuss the purpose and function of the fuel-pressure regulator. List the types of fuel-injection systems.

ELECTRONIC FUEL-INJECTION OPERATION

Electronic Fuel-Injection Operation Use powertrain control module (PCM) to control operation of fuel injectors, other functions Based on information sent to PCM from various sensors

Electronic Fuel-Injection Operation Most electronic fuel-injection systems have: Electric fuel pump (usually located inside fuel tank) Fuel-pump relay (usually controlled by the computer)

Electronic Fuel-Injection Operation Most electronic fuel-injection systems have: Fuel-pressure regulator (rubber diaphragm maintains proper fuel pressure) Fuel-injector nozzle or nozzles

Electronic Fuel-Injection Operation Most electronic fuel-injection systems use computer to control: Pulsing fuel injectors on and off Operating fuel pump relay circuit

Electronic Fuel-Injection Operation Computer-controlled fuel-injection systems normally reliable systems Use gasoline flowing through injectors to lubricate and cool injector electrical windings and pintle valves

Electronic Fuel-Injection Operation Two types of electronic fuel-injection systems Throttle-body-injection (TBI) type Delivers fuel from nozzle(s) into air above throttle plate

Electronic Fuel-Injection Operation Two types of electronic fuel-injection systems Port fuel-injection-type Uses nozzle for each cylinder

Electronic Fuel-Injection Operation Two types of electronic fuel-injection systems Port fuel-injection-type Fuel squirted into intake manifold about 2–3 inches (70–100 mm) from intake valve

Figure 78-1 Typical port fuel-injection system, indicating the location of various components. Notice that the fuel-pressure regulator is located on the fuel return side of the system. The computer does not control fuel pressure. But does control the operation of the electric fuel pump (on most systems) and the pulsing on and off of the injectors.

Figure 78-2 A dual-nozzle TBI unit on a Chevrolet 4.3-L V-6 engine. The fuel is squirted above the throttle plate where the fuel mixes with air before entering the intake manifold.

Figure 78-3 A typical port fuel-injection system squirts fuel into the low pressure (vacuum) of the intake manifold, about 2 to 3 in. (70 to 100 mm) from the intake valve.

SPEED-DENSITY FUEL-INJECTION SYSTEMS

Speed-Density Fuel-Injection Systems One of two methods for measuring amount of air engine is breathing in to match correct fuel delivery Does not require air quantity sensor

Speed-Density Fuel-Injection Systems Computer calculates amount of fuel required by engine from sensor information MAP sensor: value of intake (inlet) manifold pressure (vacuum) direct indication of engine load

Speed-Density Fuel-Injection Systems Computer calculates amount of fuel required by engine from sensor information TP sensor: position of throttle plate and its rate of change part of equation to calculate proper amount of fuel to inject

Speed-Density Fuel-Injection Systems Computer calculates amount of fuel required by engine from sensor information Temperature sensors: engine coolant temperature (ECT) and intake air temperature (IAT) used to calculate air density and engine’s need for fuel

Speed-Density Fuel-Injection Systems Computer calculates amount of air in each cylinder from manifold pressure and engine RPM Amount of air in each cylinder major factor in determining amount of fuel needed

Speed-Density Fuel-Injection Systems Formula to determine injector pulse width (PW) in milliseconds (ms): Injector pulse width = MAP/BARO × RPM/maximum RPM

Speed-Density Fuel-Injection Systems Formula modified by values from other sensors: Throttle position (TP) Engine coolant temperature (ECT)

Speed-Density Fuel-Injection Systems Formula modified by values from other sensors: Intake air temperature (IAT) Oxygen sensor voltage (O2S)

Speed-Density Fuel-Injection Systems Formula modified by values from other sensors: Adaptive memory Fuel injector delivers atomized fuel into airstream where it is instantly vaporized

MASS AIRFLOW FUEL-INJECTION SYSTEMS

Mass Airflow Fuel-Injection Systems Formula used by mass airflow fuel-injection systems to calculate injection base pulse width: Injector pulse width = airflow/RPM

Mass Airflow Fuel-Injection Systems Formula modified by values from other sensors: Throttle position Engine coolant temperature

Mass Airflow Fuel-Injection Systems Formula modified by values from other sensors: Barometric pressure Adaptive memory

Throttle-Body Injection Computer controls injector pulses in one of two ways: Synchronized Injector pulses once for each distributor reference pulse Dual injector system: injectors pulse alternately

Throttle-Body Injection Computer controls injector pulses in one of two ways: Nonsynchronized Injectors pulsed once during given period Completely independent of distributor reference pulses

Throttle-Body Injection Computer controls injector pulses in one of two ways: Injector always opens same distance Fuel pressure maintained at controlled value by pressure regulator

Throttle-Body Injection Computer controls injector pulses in one of two ways: Amount of fuel delivered by injector depends on amount of time (on-time) nozzle is open This is injector pulse width—on-time in milliseconds

Throttle-Body Injection Computer controls injector pulses in one of two ways: PCM commands variety of pulse widths to supply amount of fuel engine needs Long pulse width delivers more fuel

Throttle-Body Injection Computer controls injector pulses in one of two ways: PCM commands variety of pulse widths to supply amount of fuel engine needs Short pulse width delivers less fuel ?

Figure 78-4 The tension of the spring in the fuel-pressure regulator determines the operating pressure on a throttle-body fuel-injection unit.

Port-Fuel Injection Advantages of port fuel-injection design also related to characteristics of intake manifolds Fuel distribution equal to all cylinders: each cylinder has own injector Fuel injected almost directly into combustion chamber

Port-Fuel Injection Advantages of port fuel-injection design also related to characteristics of intake manifolds Because manifold does not have to carry fuel to properly position TBI unit, can be shaped and sized to tune intake airflow to achieve specific engine performance characteristics

Port-Fuel Injection EFI injector simply a specialized solenoid When solenoid energized, it unseats valve to inject fuel EFI systems use spray atomized fuel in timed pulses into manifold or near intake valve

Port-Fuel Injection Systems have injector for each cylinder, but may fire injectors in different ways Grouped Double-Fire Divides injectors into two equalized groups

Port-Fuel Injection Grouped Double-Fire Groups fire alternately Once each crankshaft revolution, or twice per four-stroke cycle

Port-Fuel Injection Grouped Double-Fire Fuel injected remains near intake valve and enters engine when valve opens Sometimes called gang fired

Port-Fuel Injection Simultaneous Double-Fire Fires all injectors at same time once every engine revolution Many port fuel-injection systems on four-cylinder engines use pattern

Port-Fuel Injection Simultaneous Double-Fire Easier for engineers to program system Can make relatively quick adjustments in air–fuel ratio Still requires intake charge to wait in manifold varying lengths of time

Port-Fuel Injection Sequential Sequential firing of injectors according to engine firing order Most accurate and desirable method of regulating port fuel injection

Port-Fuel Injection Sequential Also most complex and expensive to design and manufacture Each cylinder receives one charge every two crankshaft revolutions, just before intake valve opens

Port-Fuel Injection Sequential Mixture never static in intake manifold Mixture adjustments can be made almost instantaneously

Port-Fuel Injection Sequential Major advantage: intake manifolds only contain air, not air–fuel mixture Allows long, “tuned” intake-manifold runners Helps engine produce increased torque at low engine speeds

Figure 78-5 The injectors receive fuel and are supported by the fuel rail.

Figure 78-6 Cross-section of a typical port fuel-injection nozzle assembly. These injectors are serviced as an assembly only; no part replacement or service is possible except for replacement of external O-ring seals.

Figure 78-7 Port fuel injectors spray atomized fuel into the intake manifold about 3 inches (75 mm) from the intake valve.

Figure 78-8 A port fuel-injected engine that is equipped with long, tuned intake manifold runners.

Fuel-Pressure Regulator Typically consists of spring-loaded, diaphragm-operated valve in metal housing Works with fuel pump to maintain required pressure drop at injector tips

Fuel-Pressure Regulator For excess fuel (80%–90% of fuel delivered) to return to tank Fuel pressure must overcome spring pressure in diaphragm to uncover return line to tank

Fuel-Pressure Regulator For excess fuel (80%–90% of fuel delivered) to return to tank Happens when system pressure exceeds operating requirements

Fuel-Pressure Regulator Regulator shuts off return line when fuel pump not running Maintains pressure at injectors for easy restarting and reduces vapor lock ?

Figure 78-9 A typical port fuel-injected system showing a vacuum-controlled fuel-pressure regulator.

Figure 78-10 A typical fuel-pressure regulator that has a spring that exerts 46 pounds of force against the fuel. If 20 inches of vacuum are applied above the spring, the vacuum reduces the force exerted by the spring on the fuel, allowing the fuel to return to the tank at a lower pressure.

VACUUM-BIASED FUEL-PRESSURE REGULATOR

Vacuum-Biased Fuel-Pressure Regulator Many port fuel-injected systems use vacuum-controlled fuel-pressure regulator to ensure constant pressure drop across the injectors Pressure inside intake manifold changes as load on engine increases

Vacuum-Biased Fuel-Pressure Regulator

ELECTRONIC RETURNLESS FUEL SYSTEM

Electronic Returnless Fuel System ERFS does not use mechanical valve to regulate rail pressure Fuel pressure at rail sensed by pressure transducer

Electronic Returnless Fuel System Transducer sends low-level signal to controller Controller calculates a signal to pump power driver

Electronic Returnless Fuel System Power driver contains high-current transistor controlling pump speed using pulse width modulation (PWM) System capable of continuously varying rail pressure

Figure 78-12 The fuel-pressure sensor and fuel-temperature sensor are often constructed together in one assembly to help give the PCM the needed data to control the fuel-pump speed.

MECHANICAL RETURNLESS FUEL SYSTEM

Mechanical Returnless Fuel System First production returnless systems employed MRFS approach Has bypass regulator to control rail pressure Located in close proximity to fuel tank

Mechanical Returnless Fuel System Fuel sent by in-tank pump to chassis-mounted inline filter Excess fuel returns to tank through short return line System limited to constant rail pressure (CRP) system calibrations

Figure 78-13 A mechanical returnless fuel system. The bypass regulator in the fuel filter controls fuel line pressure.

Demand Delivery System (DDS) Combines control attributes of ERFS and cost and reliability attributes of MRFS Also addresses pulsation dampening/hammering, fuel transient response Different form of demand pressure regulator

Demand Delivery System (DDS) Mounts at port entry and regulates pressure downstream at injectors Admits precise quantity of fuel into rail as consumed by engine Improves pressure response to flow transients, provides rail pulsation dampening

Demand Delivery System (DDS) Fuel pump and low-cost, high-performance bypass regulator used within appropriate fuel sender Pressure control valve (PCV) may also be used Can readily reconfigure existing design fuel sender into returnless sender ?

Figure 78-14 A demand delivery system uses a fuel pressure regulator attached to the fuel pump assembly.

Fuel Injectors EFI systems use 12-volt solenoid-operated injectors Injector opens same amount each time solenoid energized Amount of fuel injected depends on length of time injector remains open

Fuel Injectors By angling director hole plates, injector sprays fuel more directly at intake valves Further atomizes and vaporizes fuel before it enters combustion chamber Typically top-feed design Fuel enters top of injector

Fuel Injectors Typically top-feed design Passes through its entire length to keep it cool before being injected

Figure 78-16 A multiport fuel injector. Notice that the fuel flows straight through and does not come in contact with the coil windings.

Figure 78-17 Each of the eight injectors shown are producing a correct spray pattern for the applications. While all throttle-body injectors spray a conical pattern, most port fuel injections do not.

Central Port Injection CPI cross between port fuel injection and throttle-body injection Assembly consists of single fuel injector, pressure regulator, six poppet nozzle assemblies with nozzle tubes

Central Port Injection Central sequential fuel injection (CSFI) has six injectors in place of the one on CPI unit Hybrid injection system combines single injector of TBI with equalized fuel distribution of PFI

Central Port Injection Eliminates individual fuel rail Allows more efficient manifold tuning than otherwise possible with TBI Newer versions use six individual solenoids to fire one for each cylinder ? ?

Figure 78-18 A central port fuel-injection system.

Figure 78-19 A factory replacement unit for a CSFI unit that has individual injectors at the ends that go into the intake manifold instead of poppet valves.

FUEL-INJECTION MODES OF OPERATION

Fuel-Injection Modes of Operation All fuel-injection systems designed to supply correct amount of fuel under wide range of engine operating conditions

Fuel-Injection Modes of Operation Starting Mode When ignition turned to start position, engine cranks and PCM energizes fuel pump relay

Fuel-Injection Modes of Operation Starting Mode PCM also pulses injectors on, basing pulse width on engine speed, engine coolant temperature The colder engine is, greater the pulse width

Fuel-Injection Modes of Operation Clear Flood Mode If engine flooded, driver can depress accelerator pedal to greater than 80% to enter clear flood mode

Fuel-Injection Modes of Operation Clear Flood Mode PCM detects low engine speed and throttle-position sensor voltage high Injector pulse width greatly reduced or even shut off entirely

Fuel-Injection Modes of Operation Open-Loop Mode Occurs during warm-up before oxygen sensor can supply accurate information to PCM PCM determines injector pulse width based on values from MAF, MAP, TP, ECT, IAT sensors

Fuel-Injection Modes of Operation Closed-Loop Mode Used to modify base injector pulse width as determined by feedback from oxygen sensor

Fuel-Injection Modes of Operation Acceleration Enrichment Mode During acceleration, throttle-position voltage increases Indicates richer air–fuel mixture required

Fuel-Injection Modes of Operation Acceleration Enrichment Mode PCM supplies longer injector pulse width May even supply extra pulses to supply needed fuel for acceleration

Fuel-Injection Modes of Operation Deceleration Enleanment Mode During deceleration, leaner air–fuel mixture required Helps reduce emissions and prevent deceleration backfire

Fuel-Injection Modes of Operation Deceleration Enleanment Mode If deceleration rapid, injector may be shut off entirely and then pulsed on enough to keep engine running

Fuel-Injection Modes of Operation Fuel Shutoff Mode PCM shuts off fuel entirely during rapid deceleration Also shuts off injector when ignition turned off to prevent engine from continuing to run

Idle Control Port fuel-injection generally uses auxiliary air bypass to control idle speed Provides needed additional airflow and thus more fuel Engine needs more power when cold to maintain normal idle speed

Idle Control Needs to overcome increased friction from cold lubricating oil System maintains engine idle speed at specified value regardless of engine temperature

Idle Control PFI systems use idle air control (IAC) motor to regulate idle bypass air Also called electronic air control (EAC) valve ?

Figure 78-20 The small arrows indicate the air bypassing the throttle plate in the closed throttle position. This air is called minimum air. The air flowing through the IAC (blue arrows) is the airflow that determines the idle speed.

Stepper Motor Operation Direct-current motors that move in fixed steps from de-energized (no voltage) to fully energized (full voltage) Often has as many as 120 steps of motion Common use as idle air control (IAC) valve

Stepper Motor Operation Controls engine idle speeds and prevents stalls due to changes in engine load Typical stepper motor uses permanent magnet and two electromagnets Each electromagnetic winding controlled by computer

Stepper Motor Operation Computer pulses windings and changes their polarity Causes armature of motor to rotate 90 degrees at a time

Stepper Motor Operation Each 90-degree pulse recorded by computer as a “step” Idle airflow in TBI travels through passage around throttle and is controlled by stepper motor

Figure 78-21 Most stepper motors use four wires, which are pulsed by the computer to rotate the armature in steps.

TECH TIP “ Two Must-Do’s” For long service life of the fuel system always do the following: BACK TO PRESENTATION Avoid operating the vehicle on a near-empty tank of fuel. The water or alcohol that may be in the tank becomes more concentrated when the fuel level is low. Dirt that settles near the bottom of the fuel tank can be drawn through the fuel system and cause damage to the pump and injector nozzles. Replace the fuel filter at regular service intervals.

FREQUENTLY ASKED QUESTION How Do the Sensors Affect the Pulse Width? The base pulse width of a fuel-injection system is primarily determined by the value of the MAF or MAP sensor and engine speed (RPM). However, the PCM relies on the input from many other sensors to modify the base pulse width as needed. For example, ? BACK TO PRESENTATION TP Sensor . This sensor causes the PCM to command up to 500% (5 times) the base pulse width if the accelerator pedal is depressed rapidly to the floor. It can also reduce the pulse width by about 70% if the throttle is rapidly closed. ECT . The value of this sensor determines the temperature of the engine coolant, helps determine the base pulse width, and can account for up to 60% of the determining factors. BARO . The BARO sensor compensates for altitude and adds up to about 10% under high-pressure conditions and subtracts as much as 50% from the base pulse width at high altitudes. IAT . The intake air temperature is used to modify the base pulse width based on the temperature of the air entering the engine. It is usually capable of adding as much as 20% if very cold air is entering the engine or reduce the pulse width by up to 20% if very hot air is entering the engine. O2S . This is one of the main modifiers to the base pulse width and can add or subtract up to about 20% to 25% or more, depending on the oxygen sensor activity.

FREQUENTLY ASKED QUESTION How Can It Be Determined If the Injection System Is Sequential? Look at the color of the wires at the injectors. If a sequentially fired injector is used, then one wire color (the pulse wire) will be a different color for each injector. The other wire is usually the same color because all injectors receive voltage from some source. ? BACK TO PRESENTATION If a group- or batch-fired injection system is being used, then the wire colors will be the same for the injectors that are group fired. For example, a V-6 group-fired engine will have three injectors with a pink and blue wire (power and pulse) and the other three will have pink and green wires.

TECH TIP Don’t Forget the Regulator Some fuel-pressure regulators contain a 10-micron filter. If this filter becomes clogged, a lack of fuel flow would result. BACK TO PRESENTATION Figure 78-11 A lack of fuel flow could be due to a restricted fuel-pressure regulator. Notice the fine screen filter. If this filter were to become clogged, higher than normal fuel pressure would occur.

FREQUENTLY ASKED QUESTION Why Are Some Fuel Rails Rectangular Shaped? A port fuel-injection system uses a pipe or tubes to deliver fuel from the fuel line to the intended fuel injectors. This pipe or tube is called the fuel rail. Some vehicle manufacturers construct the fuel rail in a rectangular cross-section. ? BACK TO PRESENTATION The sides of the fuel rail are able to move in and out slightly, thereby acting as a fuel pulsator evening out the pressure pulses created by the opening and closing of the injectors to reduce underhood noise. A round cross-section fuel rail is not able to deform and, as a result, some manufacturers have had to use a separate dampener. Figure 78-15 A rectangular-shaped fuel rail is used to help dampen fuel system pulsations and noise caused by the injectors opening and closing.

FREQUENTLY ASKED QUESTION How Can the Proper Injector Size Be Determined? Most people want to increase the output of fuel to increase engine performance. Injector sizing can sometimes be a challenge, especially if the size of injector is not known. In most cases, manufacturers publish the rating of injectors, in pounds of fuel per hour (lb/hr). ? BACK TO PRESENTATION The rate is figured with the injector held open at 3 bars (43.5 PSI). An important consideration is that larger flow injectors have a higher minimum flow rating. Here is a formula to calculate injector sizing when changing the mechanical characteristics of an engine. Flow rate = hp × BSFC/# of cylinders × maximum duty cycle (% of on-time of the injectors) hp is the projected horsepower. Be realistic! BSFC is brake-specific fuel consumption in pounds per horsepower-hour. Calculated values are used for this, 0.4 to 0.8 lb. In most cases, start on the low side for naturally aspirated engines and the high side for engines with forced induction. # of cylinders is actually the number of injectors being used. Maximum duty cycle is considered at 0.8 (80%). Above this, the injector may overheat, lose consistency, or not work at all. For example: 5.7 liter V-8 = 240 hp × 0.65/8 cylinders × 8 = 24.37 lb/hr injectors required

FREQUENTLY ASKED QUESTION What Is Battery Voltage Correction? Battery voltage correction is a program built into the PCM that causes the injector pulse width to increase if there is a drop in electrical system voltage. Lower battery voltage would cause the fuel injectors to open slower than normal and the fuel pump to run slower. ? Both of these conditions can cause the engine to run leaner than normal if the battery voltage is low. Because a lean air–fuel mixture can cause the engine to overheat, the PCM compensates for the lower voltage by adding a percentage to the injector pulse width. This richer condition will help prevent serious engine damage. The idle speed is also increased to turn the alternator faster if low battery voltage is detected. BACK TO PRESENTATION

FREQUENTLY ASKED QUESTION Why Does the Idle Air Control Valve Use Milliamperes? Some Chrysler vehicles, such as the Dodge minivan, use linear solenoid idle air control valves (LSIAC). The PCM uses regulated current flow through the solenoid to control idle speed and the scan tool display is in milliamperes (mA). ? BACK TO PRESENTATION Closed position = 180 to 200 mA Idle = 300 to 450 mA Light cruise = 500 to 700 mA Fully open = 900 to 950 mA

Halderman ch078 lecture

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