Electronic Fuel Injection Chapter 30 Electronic Fuel Injection

Electronic Fuel Injection The ideal fuel ratio is called stoichiometric This means all of the fuel and oxygen are completely consumed during combustion The ideal environment rarely exists The FI system adjusts to changes for starting, maximum power, and maximum economy

Basic EFI The PCM must know the amount of air entering the engine In MAP sensor systems, air flow is calculated based on intake manifold pressure and RPM – called a speed density system MAF sensor systems directly measure incoming air flow

Basic EFI (Cont.) During closed loop the PCM relies on input from sensors to adjust the air/fuel ratio The PCM uses inputs and look-up tables in memory to determine the ideal mixture During starting and wide-open throttle the system is in open loop

Open and Closed Loop

Fuel Injectors Electromechanical devices that meters and atomize fuel

Fuel Injectors (Cont.) The amount of fuel injected depends on fuel pressure and injector pulse width time Typical pulse width is 1 – 10 ms at full load Primary factors are load and engine temperature Injector design and fuel additives help reduce injector tip deposits and clogging

Idle Speed Control On non-ETC engines, idle speed controlled with bypass air

Idle Speed Control (Cont.) The PCM increases or decreases idle air bypass depending on engine speed, temperature, and load During cold starts, the PCM keeps idle speed high to raise catalytic converter temperature

Inputs Injector control based on sensor input MAF sensors measure incoming air volume and density MAP sensors detect changes in intake manifold pressure O2 sensors monitor exhaust oxygen content IAT sensors measure incoming air temperature ECT sensors monitor engine coolant temperature

Mass Airflow Sensor

MAP Sensor

Inputs (Cont.) O2 sensors monitor exhaust oxygen content IAT sensors measure incoming air temperature ECT sensors monitor engine coolant temperature

IAT

ECT

Inputs (Cont.) TP sensors are used to clarify load and operating conditions CKP sensors monitor engine speed CMP sensors used to synchronize injector firing VSS is used to further define operating conditions

TP Sensor

VSS

Additional Input Information Sensors Additional sensors are used to provide information regarding: Detonation Air conditioner operation Gearshift lever position Battery voltage EGR valve position

Operational Modes Starting Run Clear Flood Acceleration Deceleration

Knowledge Check Describe why so many inputs are used to control the fuel injection system. Multiple sensors are used so the PCM can provide the most accurate amount of fuel delivery possible for any given operating condition.

Starting Mode Fuel pump activated for two seconds and after CKP reference received Injector pulse width determined by: ECT, MAF, IAT, and TP

Run Mode Once a predetermined RPM is reached, system goes into open loop Injector pulse width set by: MAF or MAP, IAT, ECT, TP Closed loop begins based on input from the ECT and O2 sensors

Closed Loop

Clear Flood Mode If too much fuel is received, it must be pumped out of the cylinders Fully depress accelerator pedal and crank engine PCM detects wide open throttle and cranking RPM

Acceleration Mode Based on signals from TP and MAF or MAP To compensate, the PCM increases injector pulse width Once the PCM determines the vehicle is no longer accelerating, the system returns to run mode

Deceleration Mode Inputs from MAF or MAP and TP used to determine deceleration PCM reduces injector pulse width Some systems completely shut the injector off during rapid deceleration

Fuel Trim PCM constantly monitors HO2S or air-fuel ratio sensors in closed loop Alters injector pulse width to provide the best driveability, economy, and emission control Expressed as a percentage Base pulse width is 0 percent

Fuel Trim

Fuel Trim (Cont.) The system allows for short term (STFT) and long term (LTFT) changes LTFT are changes to set a new pulse width

Knowledge Check Technician A says positive fuel trim means the PCM is adding fuel beyond the base calculation. Technician B says excessive positive fuel trim indicates a lean exhaust condition. Who is correct? Both Technicians A and B

Throttle Body Injection (TBI) Used to move from carburetors to fuel injection Use one or two injectors over the throttle plate Not as efficient as port fuel injection No longer in use Fuel pressure typically 10 – 15 psi

Port Fuel Injection (PFI) At least one injector per cylinder Delivers fuel just outside combustion chamber Allows for good atomization Several different types used over years: Multiport injection (MPI) Sequential fuel injection (SFI)

Multi-Port Injection (MPI) The injectors are arranged and fired together in groups or pairs No longer in use Fuel charge must wait for intake valve to open MPI systems are commonly speed density systems

Sequential Fuel Injection (SFI) Sequential Injection (SFI) Each injector is fired individually just before the intake valve for that cylinder opens Typically use MAF sensors Injectors fire according to CKP

Throttle Body Controls air entering the engine and vacuum in the intake May contain a MAP sensor, IAC assembly, throttle plate(s), and TP sensor Many throttle body bores and plates coated with a special coating to prevent carbon buildup

Fuel Delivery Injectors controlled separately by PCM Fuel supplied to the injectors by the fuel rail The rail may contain a pressure test port V engines usually have left and right rails Some engines use variable intake runners for high and low speed operation

Typical Fuel Rail

Pulsation Damper Reduces pulsations caused by rapid opening and closing of injectors

Injector Control Injector opening timed to occur before the intake valve opens SFI engines require CKP and CMP input to fire each injector

Pressure Regulators MPI injector tips are located in the intake manifold where constant changes in vacuum affect fuel delivery The fuel pressure regulator adjusts fuel pressure to maintain a constant pressure drop for each injector

Returnless Systems Most newer systems have the pressure regulator as part of the fuel sender/pump Only the fuel needed by the engine is filtered and sent to the injectors

Throttle-by-Wire Systems Offer improved driveability, fuel efficiency, and decreased emissions The PCM controls a DC throttle plate motor based on input from accelerator position sensors Redundant sensors and springs are used for safety and limp-in operation

Central Multi-Port Fuel Injection Uses one central injector Fuel is delivered to individual poppet nozzles Fuel pressure is higher than most PFI systems Poppet nozzles snap into lower intake Each nozzle contains a check ball and spring The nozzle opens when pressure exceeds 37 – 43 psi

Gasoline Direct-Injection Systems Used for many years on diesel engines Highly pressurized fuel is sprayed directly into the cylinders

Injectors Special injectors seal after fuel is sprayed Fuel pressure is much higher than standard MPI systems High voltage injector drivers also required Fuel can be injected at any time

Gasoline Direct Injection (GDI) Features Allows for very lean air/fuel mixtures Increases volumetric efficiency Uses very high fuel pressures (typically between 400 and 2000 psi) System operates similarly to diesel injection systems

Typical GDI System

High Pressure Fuel Pump Gas is delivered to the engine by an in-tank pump A mechanical, high-pressure pump increases fuel pressure to between 435 to 1885 psi Pressure regulated by input from fuel rail pressure sensor

Operational Modes Lean Burn Stoichiometric Full Power Can run as high as 60:1 Stoichiometric During medium load Full Power During heavy loads and hard acceleration

Compression Ratios The ability to change air/fuel ratios eliminates spark knock, allowing higher compression ratios Does not require higher octane fuel Smaller fuel droplets cool the cylinder Mixture burns more quickly Less need for spark advance

Advantages of GDI Increased fuel economy High power output Increases engine volumetric efficiency Lowers engine thermal loss Decreases emissions Allows higher compression Reduces most turbo lag when turbocharged

GDI plus SFI Some engines use a combination of direct and indirect injection Each cylinder has two injectors PCM shuts off port injection when not needed Both injectors operate during cold starts

Knowledge Check Technician A says GDI systems use high-pressure mechanical pumps to deliver fuel to the injectors. Technician B says GDI systems also use PFI injectors. Who is correct? Both Technicians A and B