Fuel_Injection_System

1、Fuel Injection System Fuel Injection System Uses pressure (not Vacuum) from an electrical pump to spray fuel into the intake manifold. Provides the engine with proper air-fuel ratio (14.7 : 1) Fuel Injection System Advantages Improved Atomization Better fuel flow Smoother idle Improved fuel economy

2、Lower emissions Better cold weather drivability Increased engine power Simpler Fuel Injection System Atmospheric Pressure Pressure formed by the air surrounding the earth. Atmospheric pressure is 14.7psi at sea level. Any space with less than 14.7psi at sea level has vacuum. Engine acts as a vacuum

3、pump, producing vacuum in the intake manifold. Fuel Injection System Engine Throttle Valve Controls air flow and gasoline to power engine. When butterfly valve is closed it restricts air-flow and the resulting flow of fuel into the engine. When accelerator is pressed, the air-flow is increased in th

4、e intake manifold. Engine sensors detect the resulting changes and increase fuel flow through the injectors. Fuel Injection System Electronic Fuel Injection uses various engine sensors and control module to regulate the opening and closing of injector valve. Fuel delivery system Air induction system

5、 Sensor system Computer control system Fuel Delivery system Electrical Fuel Pump draws fuel from tank and forces it into the regulator. Pressure Regulator controls the amount of pressure that enters the injector and any extra fuel is returned to the fuel tank. Fuel Injector is simply a coil or solen

6、oid operated valve. Spring pressure holds the injector closed. When engaged, the injector sprays fuel into the engine. Injector Pulse Width indicates the time each Injector is energized (Kept Open). Air Induction System Air filter Throttle valve Sensors Connecting ducts Sensor System Monitors engine

7、 operating condition and reports this information to ECM (computer). Sensors are electrical devices that change resistance or voltage with change in condition such as temperature, pressure and position. Computer Control System Uses electrical data from the sensors to control the operation of the fue

8、l injectors. Engine Control Module (ECM)- “Brain” of the electronic fuel injection. Engine Sensors Oxygen Sensor measures the oxygen content in engine exhaust. Mounted on the exhaust system before the catalytic converter. Voltage out-put of O2 sensor changes with the change in oxygen content of exha

9、ust. Lean mixture decreases the voltage. Rich mixture increases the voltage. Signal is sent to ECM and the ECM changes the time that an injector is open or close. Engine Sensors Open Loop When the electronic injection system doesnt use the input from the engine exhaust. System operates on informatio

10、n stored in the computer (PROM). Computer ignores the sensors when the engine is cold. Closed Loop Ones engine reaches the operating temperature, computer uses information from oxygen sensor and the other sensors. Engine Sensors Manifold Absolute Pressure Sensor (MAP) Measures the pressure, or vacuu

11、m inside the engine intake manifold. Manifold pressure = Engine load High pressure (low intake vacuum) = High load = Rich mixture Low pressure (high intake vacuum) = Little load = Lean mixture Computer senses the change in resistance and alters the fuel mixture. Engine Sensors Throttle Position Sens

12、or (TPS) Variable resister connected to the throttle plate. Change in throttle angle = change in resistance. Based on the resistance, ECM richens or leans the mixture. Engine Sensors Engine Temperature Sensor Monitors the operating temperature of the engine. Exposed to engine coolant. Engine cold =

13、Low Resistance = Rich Mixture Engine Hot = High Resistance = Lean Mixture. Engine Sensors Mass Air Flow Sensor (MAF) Measures the amount of outside air entering the engine. Contains an air flap or door that operates a variable resistor. Helps computer to determine how much fuel is needed. Engine Sen

14、sors Inlet Air Temperature Sensor Measures the temperature of air entering the engine. Cold air (more dense) = More fuel for proper AF ratio. Engine Sensors Crankshaft Position Sensor Detects engine speed. Changes injector timing and duration. Higher engine speed = More fuel Engine Sensors Engine Id

15、le Speed Control Fast Idle Thermo Valve Thermo wax plunger expands and shrinks as the engine warms up or cools down. The thermo valve opens when cold to allow air to by-pass the throttle valve. This extra air increases engine idle speed to prevent cold engine stalling. Engine Idle Speed Control Idle

16、 Air Control Motor (IAC) Computer opens the valve when temperature sensor signals a cold engine. Open = More Air = Increased Idle Speed. Throttle Body Injection Uses one or two injectors. Injectors (pulse) spray fuel into the top of throttle body air horn. Atomized fuel mixes with air and drawn into

17、 the engine. Fuel pressure regulator is spring loaded and is part of the housing. Fuel is being injected whenever the engine is running, also called CIS: Continuous Injection System. EFI EFI Multi port Injection System Injector is pressed into the runner(Port) in the intake manifold. Injector sprays

18、 towards an engine intake valve. EFI Direct fuel Injection System Injectors are pressed into the combustion chamber and spray fuel directly into the combustion chamber. Each cylinder has its own injector Fuel Injection Diagnosis *Do not be confused with ignition or engine mechanical problems. Fuel l

19、eaks. Vacuum leaks. Kinked lines. Loose or corroded electrical connections. Sensor problems. *Do not disconnect EFI harness terminal when ignition in “on” position. Diagnosis OBD (On Board Diagnostics) & OBD II Most EFI systems have on-board diagnostic abilities. ECM can detect and record possible f

20、aults. MIL (Malfunction Indicator Light) in the dash-board glows when any abnormality is sensed. Scan tool will find and display many problems. Always scan for trouble codes before attempting other diagnostic procedures or disconnecting the battery (will clear codes). Diagnosis Pressure Regulator Te

21、sting *Caution Relieve fuel pressure (up to 60psi)before disconnecting line. Bleed Relief Valve or Fuse Check fuel pressure with fuel pressure gauge and match readings against the specs. Fuel Pressure Too Low Check clogged fuel filter or bad electric pump. Fuel Pressure Too High Usually bad pressure

22、 regulator. Maximum Fuel Pressure Test Pinch the return line with engine running (line with smaller diameter) Check the gauge, if pressure too low, Fuel Pump, not the pressure regulator is at fault. Diagnosis Injector Testing FAIR - but weak 2. BAD - split spray pattern 3. BAD - split spray pattern

23、BAD - jetting on left side GOOD 6. BAD - feathering at top of spray Bad injector can cause Rough Idle Hard Starting Poor Fuel Economy Engine Miss Leaky Injectors will richen the fuel mixture. Dirty Injectors restricts the air- flow, causing a lean mixture. Inoperative EFI Injectors no action (Miss Fire) TBI Diagnosis Check Pressure. Fuel spray pattern can be seen into the horn. If current and fuel pressure present, injector may be bad. Regulator can be taken apart (GM). Broke spring or bad diaphragm. Multi port Diagnosis Listen for “clicking” sound at each injector w