4 Fuel Injection System Atmospheric Pressure Pressure formed by the air surrounding the earth.Atmospheric pressure is 14.7psiat sea level.Any space with less than 14.7psiat sea level has vacuum.Engine acts as a vacuum pump,producing vacuum in the intakemanifold.
5 Fuel Injection System Engine Throttle Valve Controls air flow and gasoline to power engine.When butterfly valve is closed it restricts air-flow and theresulting flow of fuel into the engine.When accelerator is pressed, the air-flow is increased in theintake manifold.Engine sensors detect the resulting changes and increase fuelflow through the injectors.
6 Fuel Injection SystemElectronic Fuel Injection uses various engine sensors and controlmodule to regulate the opening and closing of injector valve.Fuel delivery systemAir induction systemSensor systemComputer control system
7 Fuel Delivery system Electrical Fuel Pump draws fuel from tank and forces it into the regulator.Pressure Regulator controls the amountof pressure that enters the injector and anyextra fuel is returned to the fuel tank.Fuel Injector is simply a coil or solenoidoperated valve.Spring pressure holds the injector closed.When engaged, the injector sprays fuelinto the engine.Injector Pulse Width indicates the time eachInjector is energized (Kept Open).
8 Air Induction System Air filter Throttle valve Sensors Connecting ducts
9 Sensor SystemMonitors engine operating condition and reports this informationto ECM (computer).Sensors are electrical devices that change resistance or voltagewith change in condition such as temperature, pressure and position.
10 Computer Control System Uses electrical data from the sensors to control the operation ofthe fuel injectors.Engine Control Module (ECM)- “Brain” of the electronic fuelinjection.
11 Engine SensorsOxygen Sensor measures the oxygen content in engine exhaust.Mounted on the exhaust system before thecatalytic converter.Voltage out-put of O2 sensor changes withthe change in oxygen content of exhaust.Lean mixture decreases the voltage.Rich mixture increases the voltage.Signal is sent to ECM and the ECM changes the time that an injectoris open or close.
12 Engine Sensors Open Loop When the electronic injection system doesn’t use the input fromthe engine exhaust.System operates on information stored in the computer (PROM).Computer ignores the sensors when the engine is cold.Closed LoopOnes engine reaches the operating temperature, computer usesinformation from oxygen sensor and the other sensors.
13 Engine Sensors Manifold Absolute Pressure Sensor (MAP) Measures the pressure, or vacuum insidethe engine intake manifold.Manifold pressure = Engine loadHigh pressure (low intake vacuum) =High load = Rich mixtureLow pressure (high intake vacuum) =Little load = Lean mixtureComputer senses the change in resistanceand alters the fuel mixture.
14 Engine Sensors Throttle Position Sensor (TPS) Variable resister connected to thethrottle plate.Change in throttle angle =change in resistance.Based on the resistance, ECMrichens or leans the mixture.
15 Engine Sensors Engine Temperature Sensor Monitors the operating temperature of the engine.Exposed to engine coolant.Engine cold = Low Resistance = Rich MixtureEngine Hot = High Resistance = Lean Mixture.
16 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.
17 Engine Sensors Inlet Air Temperature Sensor Measures the temperature of air entering the engine.Cold air (more dense) = More fuel for proper AF ratio.
18 Engine Sensors Crankshaft Position Sensor Detects engine speed. Changes injector timing and duration.Higher engine speed = More fuel
20 Engine Idle Speed Control Fast Idle Thermo ValveThermo wax plunger expandsand shrinks as the enginewarms up or cools down.The thermo valve opens when cold to allow air to by-passthe throttle valve.This extra air increases engine idle speed to prevent cold enginestalling.
21 Engine Idle Speed Control Idle Air Control Motor (IAC)Computer opens the valve when temperature sensor signalsa cold engine.Open = More Air = Increased Idle Speed.
22 Throttle Body Injection Uses one or two injectors.Injectors (pulse) spray fuel into thetop of throttle body air horn.Atomized fuel mixes with air anddrawn into the engine.Fuel pressure regulator is spring loadedand is part of the housing.Fuel is being injected whenever the engine is running, also called CIS: Continuous Injection System.
23 EFI EFI Multi port Injection System Injector is pressed into the runner(Port)in the intake manifold.Injector sprays towards an engineintake valve.Each cylinder has it’s own injectorEFI Direct fuel Injection SystemInjectors are pressed into thecombustion chamber and spray fueldirectly into the combustion chamber.
24 Fuel Injection Diagnosis ***Do not be confused with ignition or engine mechanical problems.Fuel leaks.Vacuum leaks.Kinked lines.Sensor problems.Loose or corroded electrical connections.***Do not disconnect EFI harness terminal when ignition in“on” position.
25 Diagnosis OBD (On Board Diagnostics) & OBD II Most EFI systems have on-board diagnostic abilities.ECM can detect and record possible faults.MIL (Malfunction Indicator Light) in the dash-board glows whenany abnormality is sensed.Scan tool will find and display many problems.Always scan for trouble codes before attempting other diagnosticprocedures or disconnecting the battery (will clear codes).
26 Diagnosis Pressure Regulator Testing ***Caution – Relieve fuel pressure (up to 60psi)before disconnecting line.Bleed Relief Valve or FuseCheck fuel pressure with fuel pressure gaugeand match readings against the specs.Fuel Pressure Too LowCheck clogged fuel filter or bad electric pump.Fuel Pressure Too HighUsually bad pressure regulator.Maximum Fuel Pressure TestPinch the return line with engine running (line with smaller diameter)Check the gauge, if pressure too low, Fuel Pump, not the pressureregulator is at fault.
27 Diagnosis Injector Testing Bad injector can cause Rough Idle Hard StartingPoor Fuel EconomyEngine MissLeaky Injectors will richen thefuel mixture.FAIR - but weak2. BAD - split spray pattern3. BAD - split spray patternBAD - jetting on left sideGOOD6. BAD - feathering at top of sprayDirty Injectors restricts the air-flow, causing a lean mixture.Inoperative EFI Injectorsno action (Miss Fire)
28 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.
29 Multi port Diagnosis Listen for “clicking” sound at each injector with a stethoscope.Locate the bad injector.Using an ohm meter check for resistanceacross coil and short to ground.Infinite Resistance = Open coilZero resistance to ground = shorted.
30 Diagnosis Injector noid light Special test lights to check EFI feed circuit.Injector cleaning kit can clean partially clogged injectors.***caution – Some manufacturers do not recommend cleaning injectors(Pintel Type)
31 Oxygen Sensor Diagnosis O2 voltage cycles from about 0.2 – 0.8 Volts.0.2 volts = lean AFR0.8 volts = Rich AFRSimulate LEAN condition by pulling off a large vacuum hose.(0.2 – 0.3 volts)Simulate RICH condition by injecting propane into the air intake.(0.7 – 0.8 volts)
32 Temperature SensorsResistance can be checked by dipping it in hot Vs cold water.Cold = Low resistance.Hot = High resistance.