Basic EFI

LayoutFuel TankFuel PumpInjectorsManifold VacuumSeatPintleDiaphragmReturn LineSpring

ECM ControlsTo determine the amount of fuel required, the ECM needs to know how much air is entering the engineTwo methods for measuring airflowSpeed-DensityMass Airflow

Speed-DensityThe ECM receives input from MAP (engine vacuum)TPS (throttle position)CTS (coolant temperature)IAT (air temperature)O2 (rich/lean indicator)CKP (engine RPM)

Speed-DensityBased on the engine vacuum, engine rpm, intake air temperature, and the pre-programmed volumetric efficiency of the engine, the computer calculates the amount of air entering the engineEngine operating temperature, throttle position, and rich/lean indications from the O2 are then used to calculate/adjust the required amount of fuel

Speed DensityECMMAPCKPIATAirflowECMO2CTSTPSInjectors

Mass AirflowBased on the airflow data received from the MAF engine operating temperature, throttle position, and rich/lean indications from the O2 are used to calculate/adjust the required amount of fuel

Mass AirflowECMAirflowECMO2CTSTPSInjectorsMAFCKP

Fuel InjectorsSolenoid typeECM controls the ground side of the injector circuitPoppet typeWhen pressure reaches a predetermined level the injector is forced openDiesel, CFI, CIS

Types of Fuel InjectionThrottle Body Injection (TBI)Port Fuel Injection (PFI) (MPFI)Central Point Injection (CPI)Gasoline Direct Injection (GDI)Constant Injection System (CIS)Different manufacturers may call similar systems by different names

Throttle Body Injection (TBI)The throttle body looks similar to a carburetorThe throttle body contains the fuel injectors and usually the pressure regulatorPressure regulator does not use vacuum to cut back fuel pressure during high vacuum conditions

Port Fuel InjectionThrottle body only controls the amount of air entering the engineInjectors are located in each intake portOne injector per cylinderMay use an additional cold start injectorIntake manifold only has to deliver air therefore problems with fuel puddling are greatly reducedInjectors may be batch fired or sequentially fired (SFI)Tuned port injection operates the same as port fuel injection, except the intake manifold is designed for optimal cylinder filling

Port Fuel Injection

Port Fuel Injection

Port Fuel Injection (Batch Fired)

Cold Start Injector

Central Point Fuel InjectionUsed on GM Vortec enginesCentral injection assembly located in the lower intakeFuel flow controlled by electric solenoids in the CPI assemblyMay be batch fired or sequentially firedPressure regulator located in the CPI assemblyActual fuel injectors are mechanical Wont open unless the specified fuel pressure is presentOperates at a relatively high fuel pressure (55-61 PSI)

Central Point Fuel Injection

Central Point Fuel InjectionPoppet Injector

Central Point Fuel InjectionCPI AssemblyPressure LineReturn LinePressure RegulatorPoppet InjectorsECM Actuated Solenoid-type Injectors

Constant Injection System (CIS)Mechanical injection systemUsed extensively by the GermansAmount of fuel delivered is controlled by altering fuel pressure at the injector rather that injector on timeUses a air vane to sense engine airflow and change fuel delivery rates

Constant Injection SystemTankMechanical InjectorDifferential Pressure ValveFilterPressure RegulatorPumpAir VaneMetering Valve

Constant Injection System (CIS-E)

Idle Speed ControlIn EFI systems the ECM controls idle speedThrottle opening controlThrottle Air BypassTo increase idle speed, more air is bypassed by the throttle bladesTo decrease idle speed, less air is bypassed by the throttle blades

IDLE SPEED CONTROLTo comply with federal emissions standards, idle speed control systems are usedIdle speed controlled by electronic moduleEarlier systems, engines idled in open loopIdle systems depend on inputs to PCM

Throttle Kicker controlled by Vacuum DiaphragmElectrically controlled by solenoidOperates during engine warm up, with air conditioning on and engine overheatingSome act as a dashpot327C

Throttle Kicker and Idle Stop SolenoidElectrically controlledVacuum operated throttle kicker for additional loadAllows curb idle speed to be lowerControlled by PCMMust be adjusted327C

IDLE SPEED CONTROL MOTOR (ISC)PCM controlledReversible gear drive dc motorPCM reverses polarityHas idle tracking switchMust be adjusted325C

ISC Schematic

IDLE AIR CONTROL (IAC)Used with Fuel Injection systemsPCM controlled Stepper motorDiverts air around throttle plateDo not over extend when replacingNot adjustable

Throttle Body IAC LocationScrews into throttle bodyMust be careful to not over-tightenMust keep passages cleanCan use Scanner to diagnose idle problems

IAC SCHEMATICContains two motor windingsCan test with ohmmeter (GM are 40 - 80 ohms)Use IAC Test tool to check operationCan monitor operation with Scanner508L

IAC SCOPE PATTERNSTypical patternsCompare patterns to known good patternsSome IACs operate on 12 volts and others on less voltageIAC operates with a duty cycle

ADJUSTING CURB IDLE(Idle Hardstop or Minimum Idle speed)Minimum idle rpm is factory adjustedIdle must be adjusted correctlyPassages must be cleanSome systems, you must adjust TPS also502L

IDLE SPEED ADJUSTMENTMust shut off idle air to adjust minimum idle speedUse idle plug on TBI unitsOther systems, you just turn a screw to control air flow (idle rpm)

Ford Pulse Width Idle Control Motor (Bypass Air Valve)Depending on the % on time form the ECM the pulse width motor allows more or less air to bypass the throttle bladesIntakeThrottle BodyICM