chap59 pps Automotive technology at University of Cambridge

start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 59, the reader 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 Discuss the purpose and function of the fuel-pressure regulator List the types of fuel-injection systems Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: demand delivery system (DDS) • electronic air control (EAC) • electronic returnless fuel system (ERFS) flare • fuel rail • gang fired • gasoline direct injection (GDI) idle speed control (ISC) motor mechanical returnless fuel system (MRFS) • nonchecking port fuel-injection • pressure control valve (PCV) • pressure vent valve (PVV) sequential fuel injection (SFI) • spark ignition direct injection (SIDI) • throttle-body injection (TBI) Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ELECTRONIC FUEL-INJECTION SYSTEMS Electronic fuel-injection systems use the computer to control the operation of fuel injectors and other functions based on information sent to the computer from the various sensors Most electronic fuel-injection systems share the following: Electric fuel pump (usually located inside the fuel tank) Fuel-pump relay (usually controlled by the computer) Fuel-pressure regulator (mechanically operated springloaded rubber diaphragm maintains proper fuel pressure) Fuel-injector nozzle or nozzles See Figure 59-1 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 59–1 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 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Most electronic fuel-injection systems use the computer to control these aspects of their operation: Pulsing the fuel injectors on and off The longer the injectors are held open, the greater the amount of fuel injected into the cylinder Operating the fuel pump relay circuit The computer usually controls the operation of the electric fuel pump located inside (or near) the fuel tank The computer uses signals from the ignition switch and RPM signals from the ignition module or system to energize the fuel-pump relay circuit NOTE: This is a safety feature, because if the engine stalls and the tachometer (engine speed) signal is lost, the computer will shut off (deenergize) the fuel-pump relay and stop the fuel pump Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Computer-controlled fuel-injection systems are normally reliable systems if the proper service procedures are followed Fuel-injection systems use the gasoline flowing through the injectors to lubricate and cool the injector electrical windings and pintle valves NOTE: The fuel does not actually make contact with the electrical windings because the injectors have O-rings at the top and bottom of the winding spool to keep fuel out Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 For long service life of the fuel system always the following: Avoid operating the vehicle on a near-empty tank of fuel The water or alcohol 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 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 There are two types of electronic fuel-injection systems: Throttle-body-injection (TBI) A TBI system delivers fuel from a nozzle(s) into the air above the throttle plate Figure 59–2 A dual-nozzle TBI unit on a Chevrolet 4.3-L V-6 engine See Figure 59–3 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 59–3 A typical port fuel- injection system squirts fuel into the low pressure (vacuum) of the intake manifold, about in (70 to 100 mm) from the intake valve Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Fuel Shutoff Mode Besides shutting off fuel entirely during periods of rapid deceleration, PCM also shuts off the injector when the ignition is turned off to prevent the engine from continuing to run 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 generator (alternator) faster if low battery voltage is detected Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 IDLE CONTROL Port fuel-injection systems generally use an auxiliary air bypass which provides needed additional airflow, and thus more fuel The engine needs more power when cold to maintain its normal idle speed to overcome the increased friction from cold oil It does this by opening an intake air passage to let more air into the engine just as depressing the accelerator pedal would open the throttle valve, allowing more air into the engine The system is calibrated to maintain engine idle speed at a specified value regardless of engine temperature Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Most PFI systems use an idle air control (IAC) motor to regulate idle bypass air The IAC is computer-controlled, and is either a solenoid-operated valve or a stepper motor that regulates the airflow around the throttle The idle air control valve is also called an electronic air control (EAC) valve When the engine is warm and restarted, the idle speed should momentarily increase, then decrease to normal idle speed This increase and then decrease in engine speed is often called an engine flare If the engine speed does not flare, then the IAC may not be working (it may be stuck in one position) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 59–24 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 is the airflow that determines the idle speed Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 STEPPER MOTOR OPERATION A digital output is used to control stepper motors Stepper motors are direct-current motors that move in fixed increments from deenergized (no voltage) to fully energized (full voltage) A stepper motor often has as many as 120 steps of motion A common use for stepper motors is as an idle air control (IAC) valve, which controls engine idle speeds and prevents stalls due to changes in engine load When using a stepper motor that is controlled by the PCM, it is very easy for the PCM to keep track of the position of the stepper motor By counting the number of steps that have been sent to the stepper motor, the PCM can determine the relative motor position Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 A stepper motor uses a permanent magnet and two electromagnets, controlled by the computer The computer pulses and changes polarity of the windings to cause the armature of the stepper motor to rotate 90 degrees at a time, each recorded by the computer as a “count” or “step” Figure 59–25 Most stepper motors use four wires, which are pulsed by the computer to rotate the armature in steps Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Why Does the Idle Air Controller Use Milliamperes? Some DaimlerChrysler vehicles, such as the Dodge minivan, use linear solenoid idle air control valves (LSIAC) The PCM uses regulation current flow through the solenoid to control idle speed and the scan tool display is in milliamperes (mA) Closed position = 180 to 200 mA Idle = 300 to 450 mA Light cruise = 500 to 700 mA Fully open = 900 to 950 mA Idle airflow in a TBI system travels through a passage around the throttle and is controlled by a stepper motor In some applications, an externally mounted permanent magnet motor called the idle speed control (ISC) motor mechanically advances the throttle linkage to advance the throttle opening Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ELECTRONIC THROTTLE CONTROL Electronic throttle control (ETC) systems, replace idle air control and serve as a cruise control servo This eliminates the mechanical linkage between the accelerator pedal and the throttle plates A typical electronic throttle control system includes the following components: Accelerator pedal position(APP) sensor Throttle valve actuator Throttle position sensor Throttle actuator module (or PCM) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The throttle plates are controlled by an electric actuator motor and the PCM Incorporated into the accelerator position sensor are two and sometimes three throttle position sensors that provide accelerator pedal position input to the PCM Figure 59–26 A GM electronic throttle control system showing the APP and TP sensors and the DC throttle actuator control (TAC) module and PCM In many systems the motor control is located inside the PCM See Figure 59–27 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Continued ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 59–27 A typical accelerator pedal position (APP) sensor showing two different output voltage signals that are used by the PCM to determine accelerator pedal position Two (or three in some applications) are used as a double check because this is a safety-related sensor Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Failure Mode The throttle blade is spring-loaded to a partially open position called the neutral position, which is about 16% to 20% open depending on the vehicle The throttle blade is driven closed to idle and driven open by the DC actuator motor The default position is usually a high idle that would allow the vehicle to be moved to the side of the road but not driven The spring-loaded neutral position is about 1200 to 1500 rpm depending on the vehicle If one of the sensors such as a TP or APP sensor were to fail, most systems will the following: Set a diagnostic trouble code (DTC) Turn on the malfunction indicator lamp (MIL) Limit engine speed and top speed although the vehicle will be driveable Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Continued ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 If a throttle valve motor failure occurred, the throttle will be fixed at the neutral position and the engine speed fixed to a fast idle and a DTC will be set and the MIL will be on Battery disconnect Throttle-body replacement ECM/PCM replacement Clearing of diagnostic trouble codes The typical relearn procedure includes: Turn off all electrical loads Operate engine at normal operating temperature Allow the engine to idle for 10 minutes Verify idle quality Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY A fuel-injection system includes the electric fuel pump and fuel pump relay, fuel-pressure regulator, and fuel injectors (nozzles) The two types of fuel-injection systems are the throttle-body design and the port fuel-injection design The two methods of fuel-injection control are the speeddensity system, which uses the MAP to measure the load on the engine, and the mass airflow, which uses the MAF sensor to directly measure the amount of air entering the engine Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) The amount of fuel supplied by fuel injectors is determined by how long they are kept open This opening time is called the pulse width and is measured in milliseconds The fuel-pressure regulator is usually located on the fuel return on return type fuel-injection systems TBI-type fuel-injection systems not use a vacuum-controlled fuel-pressure regulator, whereas many port fuel-injection systems use a vacuum controlled regulator to monitor equal pressure drop across the injectors Other fuel designs include the electronic returnless, the mechanical returnless, and the demand delivery systems Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458