Chapter 41 - Gasoline Injection Fundamentals

Crankshaft Position Sensor

A crankshaft position sensor is used to detect engine speed. It allows the ECM to change injector timing and duration with changes in engine rpms. Higher engine speeds generally require more fuel.

multiport injection.

A multiport injection system has fuel injectors in the intake ports (air-fuel runners, or passages, going to each cylinder). Gasoline is sprayed into each intake port, toward each intake valve. One injector is provided for each engine cylinder. Some early designs also had a cold-start fuel injector to richen the fuel mixture in the engine manifold for cold engine startup.

Solenoid Fuel Injector Parts

A solenoid fuel injector used in a multipart system typically consists of the following components: • Electric terminals—Electric terminals are electrical connections that complete the circuit between the injector coil and electronic control module. • Injector solenoid—The injector solenoid is an armature and coil assembly that opens and closes the needle valve. • Inlet screen—The inlet screen filters and traps debris before it can enter the injector nozzle. • Needle valve—The needle valve is located on the end of the armature and seals against the needle Seat. • Needle seat—The needle seat is a round hole in the end of the injector that seals against the needle valve tip. • Return spring—The return spring returns the needle valve to the closed position. • 0-ring seal—The 0-ring seal fits around the outside of the injector body and seals in the intake manifold. • Injector nozzle—The injector nozzle is an opening in the injector tip that produces the fuel spray pattern. When the ECM grounds the injector circuit. a magnetic field expands around the injector windings to magnetically attract a spring-loaded iron or steel armature. The magnetic field overcomes spring tension and pulls the injector valve open to spray fuel into the engine's intake ports or combustion chamber. When the windings are not energized. spring pressure holds the injector closed. keeping fuel from entering the engine. A solenoid fuel injector used in a multiport system is usually press-fit into the runner (port) in the intake manifold. Each injector is aimed to spray fuel toward an engine intake valve.

Solenoid Fuel Injectors

A solenoid fuel injector uses a small set of coil winding to produce an electromagnet inside the injector housing.

Airflow Sensor

An airflow sensor is used in many EFI systems to measure the amount of outside air entering the engine. This helps the ECM determine how much fuel is needed. Information is then sent to the ECM indicat-ing air inlet volume.

Intake Air Temperature Sensor

An intake air temperature sensor measures the temperature of the air entering the engine. Cold air is denser than warm air. requiring more fuel for the proper air-fuel ratio. The intake air temperature sensor helps the computer compensate for changes in outside air temperature and maintain an almost perfect air-fuel mixture ratio.

Pulse Width and Fuel Ratio

Computer pulse width is used to control how much fuel is injected into the engine. A longer pulse width or duty cycle richens the fuel mixture. A shorter pulse width or duty cycle leans the mixture because the injectors are not opened as long on each pulse. If the engine is accelerated for passing speeds. the ECM will lengthen the injector pulse width to richen the air-fuel mixture for more power. Under low load and engine power operating conditions. the ECM shortens the injector pulse width. With the injectors closed a larger percentage of the time, the air-fuel mixture is leaner. producing better fuel economy. but less power. If the engine temperature sensor signals the ECM that the engine is very cold, injector pulse width will be increased to spray more fuel to help start the cold engine.

Today's small cars have greatly improved fuel efficiency. Small but powerful engines squeeze more energy out of every drop of fuel.

Electronic engine controls, lighter body/frame structures, and sleeker body shapes have all helped reduce fuel consumption, conserving our natural resources.

In modem gasoline direct injection systems, it is possible to control engine speed without a throttle valve in the intake tract. Fuel injection quantity and timing can make the engine idle without the aid of a throttle valve.

However, for safety purposes, manufacturers still use a throttle valve to protect against engine runaway (engine speed keeps increasing until engine fails) if an injector starts leaking fuel or the ECM fails to close the injectors.

Accelerator pedal sensor operation

One accelerator pedal signal might increase current flow to the ECM. and the other sensor decreases current flow back to the ECM. By operating in this way. the circuit becomes more dependable since one signal must change in opposite proportion to the other. If the ECM detects any variation in circuit voltages from normal, the ECM stores a trouble code and may even disable the engine until repairs are made. The ECM then sends amplified control current to a servo motor actuator that opens and closes the engine throttle valve. The ECM can regulate acceleration, cruise consistency. and deceleration to improve fuel economy. reduce exhaust emissions. and prevent abrupt speed changes that could affect drive train service life. The ECM can also control engine speed by responding to the vehicle's gear shift sensor. traction control system. ABS, stability control. air conditioning. and other system inputs.

Throttle valves are not used on diesel engines. Why?

Removing the throttle valve and throttle body from the intake tract of an engine reduces pumping losses and improves diesel engine efficiency.

Zirconia Oxygen Sensor Operation

The ECM compares the voltage produced by the zirconia oxygen sensor to a reference voltage of approximately 450 mV (0.45 volts). If the engine's air-fuel mixture is too rich. there will be almost no oxygen in the exhaust gases. This creates a large difference in oxygen content between the sensor's inner and outer surfaces. and causes the sensor to generate a voltage of about 600 mV (0.6 volts). The voltage generated informs the ECM that a leaner mixture is required to reduce emissions. If the engine's air-fuel mixture is too lean. there will be a smaller difference in oxygen content between the sensor's surfaces. As a result. the sensor will generate a weaker voltage signal of about 300 mV (0.3 volts). The ECM will then enrich the fuel mixture and try to maintain a stoichiometric air-fuel mixture.

ECM Pulse Width

The ECM controls the injector pulse width and the amount of fuel sprayed into the engine. The ECM takes sensor readings for all critical engine operating conditions (air temperature. fuel pressure. crankshaft speed. camshaft position, transmission gear. etc.) using all power train sensors. The ECM uses electrical data from the sensors to control the operation of the fuel injectors and other engine performance-related devices. A wiring harness connects the sensors to the input of the ECM. Another wiring harness connects the output of the ECM to the fuel injectors.

Gasoline Injection Subsystems

The components of a direct electronic fuel injection system that develop high fuel pressure so that fuel can be injected directly into the combustion chambers.The five subsystems: Fuel delivery system—The fuel delivery system feeds clean. liquid gas from the storage tank to the engine. Air induction system—The air induction system filters. routes. and controls outside air flowing into the cylinders. Sensor system—The sensor system measures pressure. temperature. engine speed. and exhaust cleanliness for the engine control module (ECM). Computer control system—In the computer control system. the ECM responds to sensor signals to control the operation of the fuel injector and properly meter the precise amount of fuel into the engine. Fuel metering system—controls the amount of fuel injected into the engine. The ECM opens the injectors to meter fuel through the injectors and into the engine for burning.

Engine Throttle Valve

The engine throttle valve is a 'butterfly or flap-type valve in the throttle body assembly that controls airflow and the amount of vacuum in the intake manifold, as well as engine power output.

Indirect Injection Systems

The two common types of indirect injection systems are throttle body injection systems and multiport injection systems. In a throttle body injection system. or single-point injection. the injector nozzles are mounted in a throttle body assembly located on top of the engine.TBI was the first electronic fuel injection system used on passenger cars. Although a little more efficient than carburetors. they added little to engine power and efficiency.

Engine Throttle Valve Operation

When closed. the throttle valve restricts the flow of air and the resulting flow of fuel into the engine, producing high vacuum in the manifold. This keeps engine speed and power low for idling at low RPMs. When the driver presses the accelerator to increase engine speed. the throttle cable slides inside its housing and swings the throttle valve open, reducing the vacuum in the intake manifold. Atmospheric pressure then pushes more air into the engine intake manifold. Engine sensors detect the resulting changes and increase fuel flow through the injectors. With more air and fuel entering the cylinders. the pressure produced on the power strokes is increased. Engine speed and horsepower output then increase to accelerate the vehicle.

Throttle Return Spring/Engine

When the accelerator is released, a throttle return spring pulls the throttle valve closed. The accelerator is connected to the throttle valve in the throttle body. This valve controls airflow and engine power output. Accelerator movement slides the cable inside the housing to transfer motion to the valve on the engine.This returns the engine to idle speed. Engine idle speed is the operating speed (in RPMs) of an engine when the vehicle is in Park or Neutral. Idle speed is usually around 750 RPMs. It can be controlled by the idle air control valve. idle speed solenoid. idle speed motor. or by the direct fuel Injection system.

Narrow Band Oxygen Sensors

Zircona. and planar sensors are considered narrow band sensors. Narrow band oxygen sensors can only measure combustion efficiency near stoichiometric (chemically correct). These sensors do not allow for extremely lean or rich fuel mixture settings by the vehicle manufacturer. Zirconia oxygen sensors use zirconia and platinum to produce the voltage output that represents oxygen in the exhaust gases. The surface of the sensor is coated with platinum, which helps the sensor maintain a high operating temperature. At an operating temperature of about 600°F (315°C). the oxygen sensor's element becomes a semiconductor and generates a small voltage.

Continuous/Intermittent Fuel Injection

continuous fuel injection (injectors spray fuel when-ever engine was running) intermittent fuel injection (injectors open and close regardless of intake valve positions). Modern direct and multiport injection systems are timed with the intake valves for improved efficiency.

Other Sensors

include an A/C compressor sensor, transmission sensors. EGR sensor. and engine knock sensor. These sensors provide additional data about operating conditions affecting engine fuel needs.

Fuel Delivery System

includes an electric fuel pump, a mechanical fuel pump. a fuel filter. a pressure regulator solenoid. electronic fuel injectors (fuel flow control valves). and connecting fuel lines.

DEFI systems

control the air-fuel mixture more precisely than other designs. lowering emissions and fuel consumption while increasing engine power output. Therefore. DEFI has replaced multiport injection in most late-model vehicles.

Fuel Pressure Regulator

controls the amount of fuel pressure in the fuel rail. Both low- and high-pressure fuel injection systems require a fuel pressure regulator.

engine throttle actuator

usually a small, reversible servo motor with an emergency release. has a tiny electric clutch to engage and disengage the motor from the throttle shaft. When the ECM sends current through the engine throttle actuator in one direction. the throttle can be swung open. If the ECM reverses dc motor polarity, the throttle is pulled closed. With an electronically-controlled engine throttle, the engine does not accelerate or rev as quickly when the accelerator is pushed down abruptly. If the transmission shift lever is in Neutral or Park. the ECM may keep the engine at idle even when the gas pedal is pressed. Throttle-by-wire systems are found on both gasoline-and diesel-powered vehicles.

titania oxygen sensor

varies its internal resistance to signal the ECM. The titania sensor is smaller than a zirconia oxygen sensor. It is manufactured as a sealed unit. which makes it less susceptible to outside contamination (engine oil leak dripping on the outside of sensor. for example). Titania oxygen sensors also have the advantage of an almost instant oxygen content signal on cold startup. There is no need to use a heating element to warm a titania sensor to get it to operating temperature. A constant reference voltage is fed from the ECM to the titania oxygen sensor's positive terminal. As the oxygen content in the exhaust gas changes. The titania sensor's resistance also changes. This causes the voltage drop across the sensor to change. The control module monitors changes in voltage drop and adjusts fuel injector pulse width accordingly.

Differences in Pressure Cause Flow

A difference in pressure between two areas can be used to cause flow. An engine uses differences in pressure to force fuel and air into its cylinders. The engine acts as a vacuum pump. producing a low-pressure area (or vacuum) in the intake manifold and cylinders. This pulls air into the engine to support combustion.

Direct and Indirect Injection

There are many types of gasoline fuel injection systems. A gasoline injection system is often classified by where it injects fuel into the engine. An indirect injection system sprays fuel into the engine intake manifold. A direct injection system sprays high-pressure fuel into the engine's combustion chambers.

Electronic Fuel Injector Types

There are now two common types of electronic fuel injectors on the market: solenoid fuel injectors (electric current energized electromagnet pulls fuel valve open) and piezo fuel injectors (electric current energized crystal expands to push fuel valve open).

Since a DEFI fuel pressure regulator is normally open, any loss of electric power to or from the ECM or injector amplifier will open the fuel pressure relief valve to reduce fuel pressure.

This prevents a failed computer circuit or relief valve from fuel pressure that exceeds specifications. Most DEFI systems will stop all mechanical fuel pump pressure by blocking the fuel inlet to the pump if the OBD software in the ECM detects any problem.

Injection vs. Carb

Unlike a carburetor. the injection system uses pressure, not engine vacuum. to feed fuel into the engine. This makes a gasoline injection system very efficient. late-model vehicles use electric fuel pumps and electric solenoid-operated fuel injectors to spray gasoline into the intake manifold intake valve port, or combustion chamber. direct electronic fuel injection systems also use a supplemental mechanical fuel pump to increase system pressure.

Normal wide band oxygen sensor operation

a small sample of exhaust gases passes through the diffusion gap into the pump cell. Depending on whether the exhaust gases are rich or lean. the reference cell produces a source voltage (V,) above or below the reference voltage (V,). A rich mixture will produce high voltage and a lean mixture will produce low voltage. This source voltage is sent to the control circuit. If a rich mixture is indicated. the control circuit sends a negative pump current to pump cell. This causes the pump cell to consume hydrocarbons in the measuring chamber. If a lean mixture is indicated. the control circuit sends a positive pump current to the pump cell. causing the cell to consume excess oxygen. When the free oxygen or free fuel has been neutralized. the voltage feedback signal drops to about 450 mV (same as \c,) and no pump current is supplied to the pump cell. The pump current (from the control circuit) required to find equilibrium is an indica-tion of the engine air-fuel ratio (lambda). The pump current is very low (0.02 amps or less). The ECM converts this low current signal to a voltage signal that can be read by a scan tool.

Throttle Position Sensor

a variable resistor connected to the throttle plate shaft. Throttle shaft rotation causes the arm contact to slide on the resistor. In this way. different current levels are produced for different throttle positions. When the throttle opens or closes, the sensor changes resistance and signals the ECM. The computer then richens or leans the mixture, as needed.

DEFI system injection modes

affect combustion efficiency and engine horsepower: stratified charge mode, stoichiometric mode. and full power mode.

Fuel Rail

also called a fuel log, is a large diameter steel tube that feeds gasoline to the inlet fittings of the fuel injectors. Both indirect injection systems and direct injection systems require a fuel rail to all injectors to obtain the same amount of fuel pressure and flow. A large fuel rail is important. especially in DEFI systems. since the large volume or area inside the rail reduces pressure pulses that can affect fuel flow in these high-pressure systems.

Oxygen Sensor

also called an exhaust gas sensor or 0 sensor, measures the oxygen content in the engine's exhaust gases as a means of checking combustion efficiency. It is the primary sensor that contributes to electronic fuel injection efficiency and engine tuning. If the amount of unburned oxygen leaving the engine is too low. the engine is running too lean. If the oxygen content of the exhaust is too high. the engine is running too rich. A properly tuned fuel system should have just a little extra unconsumed oxygen in the exhaust to show all the fuel has been consumed during combustion.

Throttle-by-Wire Systems

also termed drive-by-wire systems. move the engine throttle valves electronically instead of using conventional mechanical linkage from the accelerator pedal. The accelerator pedal position sensor monitors the pedal position and sends a corresponding signal to the ECM, which signals the throttle actuator to open or close the throttle valves based on signals from the pedal position sensor.

primary oxygen sensor

also termed front 0, sensor. is used to monitor the oxygen in the exhaust gases as it leaves the engine. This indicates whether the engine's air-fuel mixture is too lean or too rich. It is located before. or in front of. the catalytic converter, usually as close to the engine as possible.

secondary oxygen sensor

also termed rear 0, sensor. is mounted downstream in the exhaust system. The rear oxygen sensor primarily monitors the catalytic converter for proper operation. Any 0 sensor mounted after the catalytic converter is referred to as a catalyst monitor. sensor closest to the number one cylinder denoted as Oxygen Sensor. Bank 1. Sensor 1. If the engine is a V-type. sensors located in the other bank are considered to be located in Bank 2. Sensors further down the exhaust stream from the engine are consecutively numbered as Sensor 2. Sensor 3. and so on. In almost all cases, the sensor with the highest number is the catalyst monitor.

Engine Idle Speed Control

an idle air control motor may also be used to help control engine idle speed. It is a solenoid- or servo motor-operated air bypass valve. It works something like a thermal or temperature-sensitive mechanical valve. but it is ECM controlled. The system's ECM opens the idle air control valve when temperature sensors signal a cold engine. This allows more air to enter the intake manifold. increasing idle speed to keep the engine from stalling. As the engine warms. the ECM gradually closes the valve. decreasing the amount of air that bypasses the throttle valve and reducing engine speed to curb idle (normal idle rpms).

stratified charge mode

an ultra-lean burn mode in which a small charge of fuel is injected into the combustion chambers during the end of the compression stroke. Lean burn is for light engine loads (low torque output) at lower engine speeds (1000 to 2000 RPMs). During stratified charge combustion, the engine piston is sliding up. compressing, and pushing the fuel spray charge up to the spark plug. When the spark plug fires, the large amount of oxygen with the small amount of gasified fuel explodes almost as quickly as it burns. The ultra-lean mode air-fuel mixture is as high as 65:1 (65 parts air to one part fuel) and can be used for short periods of time without detonation. DEFI mixtures are much leaner than in a conventional engine with multiport fuel injection. Although a stratified charge results in higher NO, emissions due to higher combustion temperatures. the catalytic converter can treat and remove this toxin from the engine exhaust.

Planar zirconia oxygen sensors

are similar to conventional zirconia sensors. but the zirconia element. electrodes. and heater are combined in a flat. laminated strip. This type of sensor is more resistant to contamination and vibration than a conventional zirconia sensor. Planar sensors also reach operating temperature much faster than a conventional zirconia sensor. This allows the computer system to enter closed loop sooner. significantly reducing cold-start hydrocarbon emissions. A lean burn oxygen sensor measures the oxygen content in the exhaust of lean-burn engines. This type of sensor can measure ratios as lean as 23:1. It has four wires and a modified zirconium dioxide element with either a thimble or planar design. The heater resistance of a lean burn oxygen sensor is 12-15 ohms. It produces discrete output voltages ranging from 0-5 volts. Some vehicles are equipped with titania oxygen sensors. A titania oxygen sensor uses a thick film of titania to detect the amount of oxygen present in the exhaust gases. It has three or four wires and 12-18 mm threads. The heater resistance of a titania oxygen sensors is 4-7 ohms.

accelerator pedal sensor

feeds an electric signal to the ECM that corresponds to pedal position. usually has a multi-wire sensor with redundant variable resistors or hall chips that send opposing signals.

Injector Pulse Width

indicates the amount of time each injector is energized and kept open.

Direct Fuel Injection

injects fuel directly into the engine combustion chambers. Older direct fuel injection systems were all-mechanical diesel injection systems. New direct fuel injection systems are both mechanical and electronic. These systems are commonly referred to as direct electronic fuel injection (DEFI). In addition to an electric fuel pump. a DEFI system uses a mechanical fuel pump and high-pressure injectors to spray fuel straight into the engine's combustion chambers. This is the most common design found on late-model engines.

Closed-loop

means that the computer is using information from the oxygen sensor and the other sensors. This information forms an imaginary loop. or circle. from the ECM. through the fuel system, into the exhaust system. and back to the ECM. Figure 41-21B. After the catalytic converter and oxygen sensor(s) heat up, an electronic gasoline injection system functions in closed loop. This lets the computer double-check the fuel mixture it is providing to the engine.

Manifold Absolute Pressure Sensor

measures the pressure, or vacuum, inside the engine intake manifold. Manifold pressure is an excellent indicator of engine load. High manifold pressure (low intake vacuum) indicates a high load. requiring a rich mixture. Low manifold pressure (high intake vacuum) indicates very little load. requiring a leaner mixture. The manifold absolute pressure sensor varies resistance with changes in engine load. This data is used by the computer to alter the fuel mixture.

Fuel Control Sensors

monitor various operating conditions and send information about these conditions to the engine control module. The most common sensors used to help control the operation of a gasoline injection system include: • Oxygen sensors—Oxygen sensors measure the amount of unburned fuel in engine exhaust. • Manifold absolute pressure (MAP) sensors—MAP sensors measure engine vacuum. The ECM uses the MAP sensor signal as a means of monitoring engine load or power output. • Throttle position sensors—Throttle position sen-sors detect the angle of the throttle valve opening in the throttle body. • Accelerator pedal sensors—Accelerator pedal sensors detect if the driver wants to increase or decrease engine speed. • Engine coolant temperature sensors—Engine coolant temperature sensors measure the engine operating temperature. • Airflow sensors—Airflow sensors measure the quantity of air entering the engine. • Intake air temperature sensor—The ECM uses signals from the intake air temperature sensors to calculate air density. • Crankshaft position sensors—Crankshaft position sensors produce a signal representing engine speed (rpms). • Camshaft position sensors---Camshaft position sensors detect the position and speed of the camshaft. • High fuel-pressure sensors—High fuel-pressure sensors measure the amount of fuel injected into the engine. • Low fuel-pressure sensors—Low fuel-pressure sensors monitor the operation of the in-tank pump. • Fuel tank temperature sensors—Fuel tank temperature sensors monitor the air pressure for fuel vapor emissions control. • Fuel temperature sensors—Fuel temperature sensors closely control the amount of fuel Injected. Cold fuel is denser than hot fuel and carries more heat energy per pound. • Vehicle speed sensors—Vehicle speed sensors are used by the ECM to determine vehicle road speed and transmission gear ratio. • Brake pedal switch sensors—Brake pedal switch sensors signal the ECM to shut off the fuel injector when the brake pedal is depressed to conserve fuel. • Hybrid control module sensors—Hybrid control module sensors tell the engine control mod-ule when the gas engine should be started to recharge the HV battery. • Traction control module sensors—Traction control module sensors tell the engine control module to reduce fuel injector pulse width and engine power output in order to prevent tire skid on acceleration or when speed in corners is too high.

Engine Coolant Temperature Sensor

monitors the operating temperature of the engine. It is mounted so that it is exposed to the engine coolant. When the engine is cold. the sensor might provide a low resistance (high current flow). The ECM would then richen the air-fuel mature for cold engine operation. When the engine warms. the cool-ant temperature sensor resistance changes so the ECM knows to make the mixture leaner.

Fuel Temperature Sensor

monitors the temperature of the fuel in the fuel rail. Fuel temperature has a slight effect on a fuel density and how much air and fuel must be atomized together to achieve a stoichiometric mixture and efficient combustion. Based on the signal from the fuel temperature sensor, the ECM can fine-tune fuel metering. ignition timing. boost pressure. and other engine operating parameters. In some vehicles. a fuel pressure sensor and a fuel temperature sensor are housed in a single unit.

Fuel Pressure Sensor

mounts on the fuel rail and sends an electronic signal. proportional to the pressure inside the rail. to the ECM. The ECM can then control fuel pump speed and/or fuel injector pulse width to compensate for variations in fuel system pressure. A fuel pressure sensor is often used in returnless fuel injection systems.

DEFT Amplifier Module

needed to increase the voltage and current signal sent from the ECM to operate the high-pressure direct injectors. High-pressure injectors used in DEFI systems often require up to 100 volts dc for proper solenoid operation. Large capacitors in the DEFI amplifier can be used to boost voltage and current to pulse the high-pressure injectors open. Check the operating voltages for injectors in service literature before connecting test instruments to the wiring harness connectors.

A fuel system service fitting

often provided on low-pressure EFI systems for releasing and measuring fuel pressure. Most high-pressure DEFI systems do not provide a service fitting in the fuel rail for obvious safety reasons. Low-pressure EFI systems operate on less than 15 psi (103 kPa). A high-pressure fuel injection system with an engine-driven fuel pump can produce over 2000 psi (13.789.5 kPa).

Atmospheric Pressure

pressure formed by the weight of the air surrounding the earth. At sea level, 14.7 psi (103 kPa) of pressure on everything. At higher altitudes, air pressure and air density drop, which lowers the amount of fuel that must be injected into the engine. Specific gauges and scan tools are used to measure atmospheric pressure in units of positive pounds per square inch (psi), Pascals, bars, or atmospheres.end Vacuum a pressure lower than atmospheric pressure that is formed in an enclosed area, also called "Suction". Many sealed parts in and on an engine contain vacuum pressure. Vacuum is measured in units of negative psi. inches of mercury. Pascals. or bars compared to outside atmospheric pressure.

The stoichiometric mode

produces a theoretically homogenous (equally mixed and dispersed) mixture of fuel and air. It provides good power and produces the lowest emissions of all DEFI modes of operation. The stoichiometric mode tries to attain a mixture of 14.7:1 by weight. To achieve this theoretically perfect air-fuel charge in the cylinders, the injector sprays fuel during the intake stroke as air is rushing through the intake port and into the area above the engine piston. The lull power charge mode produces a homogeneous, rich mixture (more fuel) that generates more combustion pressure and power. This is needed when the engine is accelerated quickly to produce more power and torque. Full power mode might use a slightly richer air-fuel mixture of about 13:1.

Timed Injection

sprays fuel into the engine during the intake or compression strokes. in relation to piston and valve action. example of timed injection is a diesel injection system that sprays fuel into its cylinders only on the compression strokes (hence. compression ignition engine without spark plugs). Combustion completely bums all of the injected fuel in about 5 milliseconds (0.005 seconds). at an engine speed of 4000 rpm. The whole combustion process forces the piston down to rotate the crankshaft. Since passenger engines are multi-cylinder, at least one cylinder is always producing pressure and power to spin the crankshaft smoothly.

open loop

the electronic fuel injection system does not use engine exhaust gas content as a main indicator of the air-fuel mixture. Instead. the system operates on preprogrammed information stored in the computer. For example. right after cold engine starting. the computer operates in open loop. See Figure 41-21A. Several sensors. especially the oxygen sensor. cannot provide accurate information before the engine reaches normal operating temperature. Therefore, the computer is set to ignore these sensor inputs when the engine is cold.

Wide Band Oxygen Sensors

toggle their output voltage to indicate either a rich or lean condition. A wide band oxygen sensor. on the other hand. can change its output gradually and in direct proportion to the oxygen content of the exhaust gases. Additionally. a wide band oxygen sensor can monitor air-fuel ratio over a much broader range above and below stoichiometric than a narrow band oxygen sensor. A wide band sensor can sense air-fuel mixture ratios between 0.9 and 2.2.1t is more complex than conventional oxygen sensors. does not produce voltage output to indicate the engine air-fuel ratio. Instead. it uses internal voltage signals to produce a small 0, sensor pump current that represents oxygen content. The 0, sensor pump cell can consume either oxygen or unburned fuel (hydrocarbons). depending on the direction of the pump current fed into the sensor from the ECM. Many factory engines and fuel systems now use a wide band 0 sensor to improve fuel metering. Off-road race cars are often retrofitted with one or two wide band oxygen sensors to better tune the race engines for high horsepower. Wide band sensors normally have five or six wires coming out of them.

OBD I (and older) vehicles oxygen sensor

use one 0, sensor located in the exhaust manifold or exhaust pipe before the catalytic convener. Vehicles with OBD II use at least two oxygen sensors: one 0, sensor before the catalytic converter and one after the catalytic converter. Refer to Figure 41-19. Using two oxygen sensors allows more precise control of fuel metering and the resulting emissions. V-12. V-10. V-8. and some high-performance V-6 engines have four oxygen sensors. if equipped with dual exhaust pipes.

throttle safety release

used in many throttle body assemblies to return engine to idle even if engine throttle actuator fails. has an electric clutch release mechanism that disengages engine throttle actuator if ECM detects a problem. If power is lost to the engine throttle actuator, the motor drive clutch is disengaged. causing a spring to pull the throttle closed to slow the engine.

Piezo Fuel Injectors

uses a crystalline ceramic material instead of an electromagnet to open the injector valve. The piezo crystal converts electrical energy directly into motion. Piezo fuel injectors are used in the direct injection systems found on modem gas and diesel engines. Current flow through the piezo crystal in one direction causes the atoms in the crystal to repel each other. physically expanding the crystal. This action pushes the injector valve open very quickly. When current flow is reversed, the piezo crystal is reduced in size. which closes the fuel injector. Because the needle valve. armature. and return spring in a piezo fuel injector are smaller and lighter than those used in solenoid-operated injectors. these components can be snapped open and closed more quickly. Consequently. a piezo injector can more precisely control fuel metering, leading to better fuel economy and reduced exhaust emissions.

DEFI fuel pressure regulator

uses an electric solenoid to bypass excess fuel pressure back to the low-pressure side of the system. The ECM controls the fuel pressure solenoid by rapidly snapping it open and closed. A solenoid-type pressure regulator is often mounted on the mechanical fuel pump or sometimes on the fuel rail. To increase fuel pressure. the ECM sends a longer duty cycle and more current to the electromagnet to force a small relief valve closed. To decrease fuel pressure, the ECM opens the ground circuit. This allows spring pressure to open the bypass valve to reduce fuel pressure.

EFI fuel pressure regulator

uses engine vacuum. not the ECM. to control fuel pressure in multipart fuel injection systems. Changes in engine vacuum and load are used to control fuel pressure. When engine vacuum is low (during rapid acceleration, for example). low air pressure in the engine intake manifold cannot overcome spring tension. The EFI fuel pressure regulator would increase fuel pressure. so more fuel is injected into the engine. The opposite is true when engine vacuum is high—when engine load and power requirements are low.

Typical gasoline injection system

uses pressure from an electric or mechanical fuel pump to spray fuel into the intake manifold (multiport or manifold injection) or combustion chambers (direct injection). must provide the engine with the correct air-fuel mixture for operating conditions.